NATL INST OF STAND 8. TECH NBSIR 78 - 894

AuiQ. ^7a_HojjEFIED NATURAL GAS RESEARCH

at the

NATIONAL BUREAU OF STANDARDS

PROGRESS REPORT FOR THE PERIOD

1 January - 30 June 1978

D.E. Oilier, Editor

QC

100

.U56

78-89^

THERMOPHYSICAL PROPERTIES DIVISION, NATIONAL ENGINEERING LABORATORY,

NATIONAL BUREAU OF STANDARDS, BOULDER, COLORADO

nanonat Bureaa oi sianaarc]: MAY 1 4 ]979

0^

NBSIR 78 - 894

LIQUEFIED NATURAL GAS RESEARCH

at the

NATIOMAL BUREAU OF STANDARDS

D.E. Diller, Editor

Thermophysical Properties Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

Progress Report for the Period

1 January - 30 June 1978

U.S. DEPARTMENT OF COMMERC^E, Juanita M. Kreps, Secretary

Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary tor Science and Tectnnology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
Prepared for:

American Gas Association, Inc.

1515 Wilson Boulevard

Arlington, Virginia 22209

LNG Density Project Steering Committee

(in cooperation with the American Gas Association, Inc.)

Pipeline Research Committee

(American Gas Association, Inc.)

Gas Research Institute

10 West 35th Street

Chicago, Illinois 60616

U. S. Department of Commerce

Maritime Administration

Washington, DC 20235

U. S. Department of Commerce

National Bureau of Standards

National Engineering Laboratory

Boulder, Colorado 80303

U. S. Department of Commerce

National Bureau of Standards

Office of Standard Reference Data

Washington, DC 20234

U. S. Department of Commerce

National Bureau of Standards

Office of International Standards

Washington, DC 2 02 34

LNG Custody Transfer Measurements Supervisory Committee

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135

American Bureau of Shipping

45 Broad Street

New York, New York 10004

ii
ABSTRACT

Thirty-one cost centers, supported by six other agency sponsors in

addition to NBS, provide the basis for liquefied natural gas (LNG) research

at NBS. During this six-month reporting period the level of effort v;as over

20 man-years/year with funding expenditures of over $500,000. This integrated

progress report, to be issued in January and July, is designed to:

1) provide all sponsoring agencies with a semiannual report on

the activities of their individual programs;

2) inform all sponsoring agencies on related research being

conducted at the Thermophysical Properties Division;

3) provide a uniform reporting procedure which should maintain

and improve communication while minimizing the time, effort

and paperwork at the cost center level.

The contents of this report will augment the quarterly progress

meetings of some sponsors, but will not necessarily replace such meetings.

Distribution of this document is limited and intended primarily for the

supporting agencies. Data or other information must be considered

preliminary, subject to change and unpublished, and therefore not for

citation in the open literature .

Key words: Cryogenics; liquefied natural gas; measurement; methane;

properties; research.
CONTENTS

Cost Center Page

REFERENCE DATA

a) THERMOPHYSICAL PROPERTIES DATA FOR PURE

COMPONENTS AND MIXTURES OF LNG COMPONENTS

(Gas Research Institute; American Gas

Association, Inc.; NASA Lewis Research

Center

)

b) FLUID TRANSPORT PROPERTIES

(NBS-Office of Standard Reference Data)

c) PROPERTIES OF CRYOGENIC FLUIDS (NBS)

d) PROPERTIES OF CRYOGENIC FLUID MIXTURES

(NBS; NBS-Office of Standard Reference

Data; AGA; GRI)

e) DENSITIES OF LIQUEFIED NATURAL GAS MIXTURES

(LNG Density Project Steering

Coininittee - AGA)

f) PROGRAI'I FOR REDUCING THE COST OF LNG SHIP

HULL CONSTRUCTION — PHASE II SHIP STEEL

IMPROVEMENT PROGRAM (Maritime

Administration)

7360574 and

7360548

7360124

7360122

7360123,

7360129 and

7364574

7361574

7361430,

7362430 and

7363430

7 10

13

16

II. MEASUREMENT SCIENCE

a) CUSTODY TRANSFER - LNG SHIPS (Maritime

Administration; LNG Custody Transfer

Measurements Supervisory Committee)

b) HEATING VALUE OF FLOWING LNG (Pipeline

Research Committee - AGA)

c) LNG DENSITY REFERENCE SYSTEM (American Gas

Association, Inc.; Gas Research Institute;

National Bureau of Standards)

d) LNG SAMPLING MEASUREMENT STUDY (Pipeline

Research Committee - AGA)

7360460, 18

7361575,

7362575,

7363575,

7310570 and

7310571

7366579 19

7367574 20

7365574 22

III. TECHNOLOGY TRANSFER

a) SURVEY OF CURRENT LITERATURE ON LNG AND

METHANE (American Gas Association, Inc.;

Gas Research Institute)

b) LIQUEFIED NATURAL GAS TECHNOLOGY TRANSFER

(Maritime Administration; American Gas

Association, Inc.; Gas Research Institute;

American Bureau of Shipping; NBS-Office

of Standard Reference Data)

c) OIML JOINT SECRETARIAT ON LNG MEASUREMENTS

(American Gas Association, Inc.; NBSOffice of International Standards;

NBS-Thermophysical Properties Division)

7369574

7360403,

7361403,

7360570,

7364574,

7368574,

7360127,

7360461 and

7360594

7361104

24

27

30

IV
CONTENTS (Continued)

Page

IV. BIBLIOGRAPHY 32

NBS Reports and Publications Related to LNG Technology

which Have Appeared Since January 1977.

V. APPENDICES

Reprints of Selected Reports and Publications

A. Tsumura, R. and Straty, G. C, "Speed of sound in A-1

saturated and compressed fluid ethane," Cryogenics 17

,

193 (1977)

.

B. Hanley, H. J. M. , Gubbins, K. E. and Murad, S., B-1

"A correlation of the existing viscosity and thermal

conductivity data of gaseous and liquid ethane,"

J. Phys. Chem. Ref. Data 6, 1167 (1977).

C. Haynes, W. M. , and Hiza, M. J., "Measurements of the C-1

orthobaric liquid densities of methane, ethane,

propane, isobutane and normal butane," J. Chem.

Thermodynamics 9_, 179 (1977 ).

D. Hiza, M. J., Haynes, W. M. and Parrish, W. R. , D-1

"Orthobaric liquid densities and excess volumes for

binary mixtures of low molar mass alkanes and

nitrogen between 105 and 140 K," J. Chem. Therm.odynamics

9, 873 (1977).

E. Parrish, W. R. , Arvidson, J. M. and LaBrecque, J. F. , E-1

"System is accurate, precise for LNG sampling," Hydrocarbon

Processing _57, 114 (1978).

F. Siegwarth, J. D. , LaBrecque, J. F. and Younglove, B. A., F-1

"Test of densimeters for use in the custody transfer of

LNG," Proceedings, International School for Hydrocarbon

Measurement, Norman, Oklahoma, April 11-14, 1978.

G. Brennan, J. A., "Better LNG flow measurement sought," G-1

Oil and Gas Journal 76, 168 (1978).

V

1. Title. THERflOPHYSICAL PROPERTIES DATA FOR PURE COMPONENTS AND

MIXTURES OF LN6 COMPONENTS

Principal Investigators . R. D. Goodwin, H. M. Roder, G. C. Straty,

W. M. Haynes, R. D. McCarty, and D. E. Diller

2. Cost Center Number . 7360574, 7360548

3. Sponsor Project Identification . Gas Research Institute Grant No.

5010-362-0019 and American Gas Association, Inc., Project BR-50-10.

National Aeronautics and Space Administration, Lewis Research Center,

Purchase Order C-78014-C.

4. Introduction . Accurate phase equilibrium, equation of state (PVT) , and

thermodynamic properties data are needed to design and optimize gas

separation and liquefaction processes and equipment, and for mass and

heat transfer calculations. Accurate data for the pure components and

selected mixtures of hydrocarbon systems will permit developing

comprehensive accurate predictive calculation methods which take into

account the dependence of the thermophysical properties of mixtures on

the composition, temperature, and density.

This project will provide comprehensive accurate thermophysical

properties data and predictive calculation methods for compressed and

liquefied hydrocarbon gases and their mixtures to support the development of LNG technology at NBS and throughout the fuel gas industry. It

will also serve as the base for a comprehensive mixtures prediction

methodology.

5. Objectives or Goals . The objectives of our work are the determination

of comprehensive accurate thermophysical properties data and predictive

calculation methods for the major pure components (methane, ethane,

propane, butanes, and nitrogen) and selected mixtures of liquefied

natural gas and hydrocarbon mixtures at temperatures between 8 0 K and

320 K and at pressures up to 35 MPa (5000 psi) . Our goal is to provide

a range and quality of data that will be recognized as definitive or standard for all foreseeable low temperature engineering calculations.

6. Background . Liquefied natural gas is expected to supply an increasing

percentage of the United States' future energy requirements. It is

likely that massive quantities of liquefied natural gas will be

imported during the years 1978 - 1990. Ships and importation terminals

are being built for transporting, storing, and vaporizing liquefied

natural gas for distribution. Accurate physical and thermodynamic

properties data for compressed and liquefied natural gas and hydrocarbon

mixtures are needed to support these projects. For example, accurate

compressibility and thermodynamic properties data are needed to design

and optimize liquefaction and transport processes; accurate data for the

heating value, which for liquefied natural gas mixtures depends on the

total volume, the density, and the composition, are needed to provide a basis for equitable custody transfer. Accurate mixture data prediction

methods are needed for use in automated heat transfer calculations.

Accurate thermodynamic properties data for liquefied gas mixtures must

be based on precise compressibility and calorimetric measurements;

compressibility data give the dependence of thermodynamic properties on pressure and density (at fixed temperatures) ; calorimetric data give

the dependence of thermodynamic properties on temperature (at fixed

pressures and densities). It is impossible, however, to perform

enough compressibility and calorimetric measurements directly on multicomponent mixtures to permit accurate interpolation of the data to

arbitrary compositions, temperatures and pressures. Instead, thermodynamic properties data for multicomponent mixtures must usually be

predicted (extrapolated) from a limited number of measurements on the

1
pure components and their binary mixtures. This project was initiated

• to provide the natural gas and aerospace industries with comprehensive

accurate data for pure compressed and liquefied methane, the most

abundant component in LNG mixtures. We have published National Bureau

of Standards Technical Note 653, "Thermophysical Properties of Methane,

From 90 to 500 K at Pressures to 700 Bar," by Robert D. Goodwin (April

1974), and National Bureau of Standards Technical Note 684, "Thermophysical Properties of Ethane, From 90 to 600 K at Pressures to

700 Bar," by Robert D. Goodwin, H. M. Roder, and G. C. Straty (August

1976) . These reports contain the most comprehensive and accurate tables

available for the thermophysical properties of pure gaseous and liquid

methane and ethane, and provide an accurate basis for calculating

thermophysical properties data for LNG and other hydrocarbon mixtures.

7 . Program and Results . 7.1 Propane, PVTx and Dielectric Constant Measurements — W. M. Haynes

The apparatus for PVT and dielectric constant measurements on propane

is now being used for measurements on liquid mixtures of LNG components.

The mixtures that have been investigated so far are listed in the report

for cost center number 7361574.

To put the apparatus into working order for propane after the mixture

measurements are completed, the following tasks need to be performed:

(a) check out the dead weight gauge measurement system,

(b) test the cell to pressures of 35 MPa; this was done before the

LNG density program, but has not been checked since the cell has

experienced many temperature cycles between 100 and 300 K, and

(c) write computer programs for reduction of the propane data.

. The LNG density measurements should be completed within the next two

months

.

7.2 Calculational Methods — R. D. McCarty

The developmental work on the extended corresponding states method is

continuing. The mapping of the equation of state of one fluid into the

equation of state of another, as has been described in previous reports,

is continuing. The application of this technique to the prediction of

. the properties of a mixture has been accomplished in the case of

methane-nitrogen mixtures. Initial comparisons between experimental

and calculated densities show only minor improvement when the shape

factors are obtained by the mapping technique indicating a need to obtain

new binary interaction parameters using the new experimental data. This

will be accomplished in the near future.

7.3 Propane, Specific Heat Data -- R. D. Goodwin

Experimental specific heats for saturated liquid propane, along the

coexistence path, have been determined from the triple-point temperature

('^^ 85 K) to 289 K. Specific heats for the compressed liquid at constant

molal volume have been determined along isochores at nine different

densities ranging from near the triple-point liquid density to about

twice the critical-point density (at pressures up to 300 bar)

.

Comparisons with previous experimental- and/or derived-data show

agreement within combined uncertainties of about three percent.

The manuscript, "Specific Heats of Saturated and Compressed Liquid

Propane," by R. D. Goodwin, has been accepted for publication in the

Journal of Research of the National Bureau of Standards, Vol. 83^ (5)

(Sep-Oct 1978)

.

2
7.4 Butane, Freliminary Thermophysical Properties Data — R. D. Goodwin

The objective is to prepare provisional tables of therinodynamic properties

of normal butane, using available physical properties data. In this

work we expect to discover those areas of properties data most in need

of further experimental measurements.

A "Bibliography of References" on n-butane was prepared June 1, 1977,

by the Cryogenic Data Center. Work on the formulation of physical

properties, needed for thermal computations, is well under way.

In general, there is an abundance of quite inconsistent data from

different laboratories, requiring tedious weightings, selections, and

eliminations. There are few data for liquid butanes at LNG temperatures.

Apparently satisfactory formulations have been developed for the virial

equation, the saturated liquid densities, specific heats for the saturated

liquid below the boiling point, and for the ideal gas thermodynamic

functions.

By thermal loops, in a procedure first developed by W. T. Ziegler, we

have derived new "data" (where none existed) from the triple- to the

boiling-point for vapor pressures, densities of the saturated vapor, and

fcr heats of vaporization. The vapor-pressure equation has been adjusted

to include these new data, and a provisional description has been

developed for the heats of vaporization up to the critical point.

At this writing, a special difficulty is found with the mass of

irregular data for densities of the saturated vapor, in developing a formulation consistent with required behavior, and with that for other

substances

.

7.5 Pure Nitrogen and Nitrogen-Methane PVTx Property Measurements —

G. C. Straty and D. E. Diller

Gas expansion PVT measurements on pure compressed and liquefied nitrogen

have been completed. About 300 measurements were made at 21 densities

in the range 11.2 - 28.4 mol/L, 80 - 270 K, 1 - 350 bars. These

measurements were made to provide more accurate pure component data for an accurate mathematical model of the PVT properties of nitrogen-methane

mixtures

.

Twelve isochoric gas-expansion PVT runs have been made on a gravimetrically prepared 50.115 mole % nitrogen-4 9 . 8 85 mole% methane mixture in

the T, P, p range 82 - 320 K, 2 - 350 bar, 11 - 28.6 mol/L. The

measurements are being compared with the extended corresponding states

model (R. D. McCarty, NBSIR 77-867 (Oct 1977)), which was previously

optimized to saturated liquid density measurements on this mixture at

temperatures below 140 K. Differences between calculated and measured

densities range from several tenths percent at low temperatures and

high densities to several percent near the critical temperature 161 K)

and critical density ("^ 10.5 mol/L). About eight more measurement runs are planned.

Problem Areas . None.

Funding . January 1 - June 30, 1978.

Man-years expended

Equipment and/or Services Purchased

Total Reporting Period Cost

Balance Remaining

0.8

3. 2K$

69.2K$

174. 9K$
10. Future Plans.

Objectives and Schedule: Quarter

Measure, analyze and report PVT and

dielectric constant data for

hydrocarbon mixtures and LNG.

Evaluate and optimize promising

calculation methods for the

thermodynamic properties of

methane-nitrogen mixtures.

Measure, analyze and report PVT and

dielectric constant data for propane.

Analyze available thermodynamic data

for the butanes and develop an accurate equation of state.

>

4
1. Title . FLUID TRANSPORT PROPERTIES

Principal Investigator . Hov'/ard J. M. Hanley

2. Cost Center Number . 7360124

3. Sponsor Project Identification . NBS-Office of Standard Reference Data

4. Introduction . Methods for predicting the transport properties of fluid

mixtures are unreliable and data are scarce. Prediction methods are

needed, however, to supply the necessary design data needed to increase

efficiency and reduce costs.

5. Objectives or Goals . The long range or continuing goal of the program

is to perform a systematic study of the theories and experimental measurements relating to transport properties, specifically the viscosity

and thermal conductivity coefficients, of simple mixtures over a wide

range of experimental conditions. The specific objectives of the program include: 1) the systematic correlation of the transport properties

of simple binary mixtures and the development of prediction techniques,

2) development of a mixture theory for the dilute gas region and the

dense gas and liquid regions, 3) extension of the theory and prediction

techniques to multicomponent systems, and 4) suggested guidelines for

future areas of experimental work,

6. Background . A continuing program has successfully expanded the stateof-the-art of transport phenomena for pure fluids. Information for pure

fluids is required as a prerequisite for mixture studies. The theory

of transport phenomena has been developed and applied to produce practical

numerical tables of the viscosity, thermal conductivity and diffusion

coefficients of simple fluids: Ar, Kr , Xe, N2 , O2 / He, H2 f CH^,^"^^

^2"6-^^^

It has been shown that a successful mixture program can emerge from

combining the results for pure fluids with mixture equation of state

studies. The equation of state work is being carried out by other

investigators in this laboratory.

7. Program and Results . A procedure to predict the transport properties of

mixtures has been developed via corresponding states . (-^"^^ The method

has been shown to be satisfactory. Current studies include the behavior

of the transport coefficients near a critical point of a binary

mixture. (2) Tables of transport properties for propane are in press. (5)

A compilation of the transport properties of ethylene has been initiated.

Theoretical studies on the properties of a 1/r^ fluid are in progress.

8. Problem Areas . The lack of suitable experimental mixture transport

properties data for comparison purposes is the main problem. Also

equation of state (PVT) data for mixtures are needed.

9. Funding . January 1 - June 30, 1978.

Allocation 63.0K$/yr.

Labor 0.5 MY 30.2K$

Other Costs 3. 0K$

Total 33.2K$

10. Future Plans . The corresponding states predictive procedure for mixtures

will be more fully developed and expanded in line with the concurrent

equation of state studies. We intend to investigate, in particular,

the behavior of the transport properties at gas/liquid and liquid/liquid

equilibria

,

5
References

1. H. J. M. Hanley, Prediction of the Viscosity and Thermal Conductivity

Coefficients of Mixtures, Cryogenics, Vol 16, No. 11, 643-51 (Nov 1976);

H. J. M. Hanley, Prediction of the Thermal Conductivity of Fluid

Mixtures, Proceedings 7th ASME Conf. on Thermophysical properties;

H. J. M. Hanley in "Phase Equilibria and Fluid Properties in the

Chemical Industry," ACS Symp. Series No. 60 (1977).

2. H. J. M. Hanley, Transport Coefficients in the One-Fluid Approximation:

Behavior in the Critical Region, J. Res. Nat. Bur. Stand. (U.S.) 82,

18 (1977).

3. H. J. M. Hanley, W. M. Haynes and R. D. McCarty, The Viscosity and

Thermal Conductivity Coefficients for Dense Gaseous and Liquid Methane,

J. Phys. Chem. Ref. Data, Vol 6, No. 2, 597-609 (1977).

4. H. J. M. Hanley, K. E. Gubbins and S. Murad , A Correlation of the

Existing Viscosity and Thermal Conductivity Coefficients of Gaseous and

Liquid Ethane, J. Phys. Chem. Ref. Data, Vol 6, No. 4, 1167 (1977).

5. H. J. M.' Hanley, P. M. Holland, K. E. Gubbins and. J. M. Haile, J. Phys.

Chem. Ref. Data (in press).

6. J. C. Rainwater and H. J. M. Hanley, Chem. Phys. Letts, (in press).

6
1. Title . PROPERTIES OF CRYOGENIC FLUIDS

Principal Investigators . G. C. Straty, H. M. Roder, L. A. Weber, B. J.

Ackerson, and D. E. Diller

2. Cost Center Number . 7360122

3. Sponsor Project Identification . NBS

4. Introduction . Accurate thermophysical properties data and predictive

calculation methods for cryogenic fluids are needed to support advanced

cryogenic technology projects. For example, liquefied natural gas is

expected to supply an increasing percentage of the United States'

energy requirements through 1990. Liquefaction plants, ships and

receiving terminals are being constructed to transport and store natural

gas in the liquid state (LNG) . Accurate thermophysical properties data

for LNG are needed to design low temperature processes and equipment.

Accurate data will benefit the energy industries and the consumer by

providing for safe and efficient operations and reduced costs. As a logical extension of properties data on LNG, are the data needs for a number of higher temperature industrial fluids such as synthetic natural

gas (SNG) . SNG mixtures can be characterized as much more complex than

natural gas, containing unlike (including highly polar) molecules.

Interactions between unlike molecules are not well understood and the

accurate data necessary to quantitatively understand the interactions

are lacking. The needs for accurate predictive methods for SNG are essentially the same as LNG, i.e., to reduce capital and operating costs

and improve energy efficiency.

5. Objectives or Goals . The objectives of this project are to provide

comprehensive accurate thermodynamic, electromagnetic and transport

properties data and calculation methods for technically important

compressed and liquefied gases (helium, hydrogen, oxygen, nitrogen,

methane, ethane, etc.) at low temperatures. In addition we intend to

develop the capability to perform accurate PVT measurements on gaseous

mixtures and pure components at high pressures and above room

temperature. Precise compressibility, calorimetric and other physical

property measurements will be performed to fill gaps and reconcile

inconsistencies. Definitive interpolation functions, computer programs

and tables will be prepared for engineering calculations. The immediate

goals of this work are to obtain accurate sound velocity and thermal

diffusivity data for compressed and liquefied gases by using laser light

scattering spectroscopy techniques; design, construct and performance

test a precision PVT apparatus for the region 250 - 900 K with pressures

to 35 MPa; and design, construct and performance test a transient hotwire thermal conductivity apparatus for the region 70 - 350 K with

pressures to 80 MPa.

6. Background . The application of laser light scattering techniques to

obtaining thermophysical properties data was initiated to complement and

check other measurement methods and to solve measurement problems

inherent in more conventional methods. For example, laser light

scattering techniques permit measurements of sound velocities for fluids

under conditions for which sound absorption is too large to perform

ultrasonic measurements; laser light scattering techniques permit

measurements of thermal dif f usivities under conditions for which

convection interferes with measurements of thermal conduction. The

feasibility of light scattering experiments to obtain data on binary

diffusion coefficients has also been demonstrated.

Light scattering allows thermal diffusivity measurements in the region

where density fluctuations are relatively large, but accuracy drops

significantly as you pass outside the extended critical region. To

complement the scattering method, thermal conductivity measurements can

7
be made with more conventional techniques such as a hot-wire technique.

In the latter method a very small platinum wire is surrounded by the

fluid and a voltage pulse is applied to the wire. The temperature of

the wire is momentarily raised and the resistance increases. A series

of very closely spaced resistance measurements would describe the return

of the wire to equilibrium. These resistance vs. time measurements can

be related to the rate of heat dissipation in the surrounding fluid and

thus the thermal conductivity (provided convection heat transfer is

prevented)

.

The development of accurate mathematical models (equation of state) for

fluid mixtures requires accurate PVT data for the pure constituents and

binary mixtures of key molecular pairs. Experience with LNG has

identified the type and accuracy of the data required. In addition to

that, work on SNG at high temperatures is a logical follow -on to the

low temperature work on LNG. Typical constituents of raw SNG from coal

via the Lurgi process are: water - 50.2%; hydrogen - 20.1%; carbon

dioxide - 14.7%; carbon monoxide - 9.2%; methane - 4.7%; ethane - 0.5%;

hydrogen sulfide and others - 0.6%.

An apparatus has been assembled for laser light scattering spectroscopy

measurements on compressed and liquefied gases (76-300 K, 35 MPa) . The

apparatus consists of a high pressure optical cell, a cryostat

refrigerated by means of liquid nitrogen, an argon ion laser and low-level

light detection equipment.

The light scattered from fluctuations in the fluid can be analyzed with

either digital autocorrelation techniques for the examination of the

very narrow lines associated v>7ith scattering from temperature

fluctuations (Rayleigh scattering) or with a scanned Fabry Perot

interferometer for the measurement of the Doppler frequency shifts

associated with the scattering from propagating density (pressure)

fluctuations (Brillouin scattering)

.

Apparatus for photon-counting and digital autocorrelation has been

assembled, interfaced with computer facilities and programmed to

enable on-line data accumulation and analysis. Initial problems

associated with signal modulations from excessive building vibrations

have been solved by levitating the apparatus on an air suspension

system. A small, highly stable capacitor has also been designed,

constructed and installed inside the scattering cell to permit the

dielectric constant of the scattering fluid to be determined, which

should allow more accurate fluid densities to be obtained for use in

the data analysis. Apparatus tests on well characterized, strongly

scattering, test fluids have been made to verify data analysis

programs.

Extensive thermal diffusivity data have been obtained for methane.

Measurements have been made along the coexistence curve, the critical

isochore, and critical isotherm. The measurements extend outside the

critical region as well as deep into the critical region. In the deep

critical region the effect of temperature gradients and impurities have

been investigated. Outside the critical region, these effects do not

affect measurements beyond experimental accuracy. The range of the

measurements extends from 150 K to 230 K and 3 mol/L to 22 mol/L. The

inaccuracy of the measurements is about 5% in the critical region,

increasing to 10% or greater further away. A detailed analysis of the

data and experimental error has been made and a paper ^-'-^ reporting the

results has been submitted to the Journal of Chemical Physics.

Some preliminary results on a mixture of 70% methane and 30% ethane

were obtained very near the vapor-liquid critical point (plait point)

.

The results are interesting in that the thermal conductivity of the

mixture does not exhibit a critical anomaly whereas pure methane does

exhibit an anomaly in the thermal conductivity as the critical point is

approached. The anomalous behavior of pure fluids and nonanomalous

8
behavior of mixtures is qualitatively and quantitatively in agreement

with theoretical predictions (see preceding title 'Fluid Transport

Properties'). We hope to be able to perform more definitive measurements

on hydrocarbon mixtures in the near future.

7. Program and Results . The transient hot-wire apparatus is nearing

completion. All parts and electronic equipment have been received.

Assembly of the sample cell is nearing completion and programs for

acquiring and processing the data have been written and checked out on

the Nova minicomputer to be used during the measurements.

No work has started on the high temperature PVT, however an Automatic

Systems Laboratory A7 automatically self-balancing thermometry bridge

has been ordered as well as two precision quartz pressure transducers.

The latter will be placed in the NBS-Pressure Calibration System to test

long term stability.

8. Problem Areas . Light scattering has proven to be a valuable tool for

obtaining thermal diffusivity data on fluids. This is particularly

true in a broad temperature and density range around the critical

point, where more conventional experimental methods fail or are severely limited. The intensity of the scattered light however

decreases drastically as one moves av/ay from the critical region.

Data accuracy in this region becomes limited by the statistical nature

' of the scattering process and the ability to maintain stability and

precise experimental parameters over the extended periods of time

necessary for data accumulation.

At the present time no funds are available to begin constructing the new

PVT apparatus. It is hoped that partial funding will become available

in October, 1978.

9. Funding . January 1 - June 30, 1978.

Man-years expended 0.2

Equipment and/or Services Purchased 30.7K$

Total Reporting Period Cost 22.0K$

Balance Remaining 18.0K$

10. Future Plans . Objectives and Schedule: Quarter 3

Design, construct and performance

test transient hot-wire thermal

conductivity apparatus.

Design, construct and performance

test high temperature-high

pressure PVT apparatus

Reference

1. B. J. Ackerson and G. C. Straty, Rayleigh Scattering from Methane,

J. Chem. Phys. (scheduled for August 1978).

9
Title . PROPERTIES OF CRYOGENIC FLUID HIXTURES

Principal Investigators . M. J. Hiza, A. J. Kidnay (part-time) , and

R. C. Miller (part-time)

.

Cost Center Numbers . 7360123, 7360129 and 7364574

Sponsor Project Identification . NBS , NBS (OSRD) , AGA, GRI

Introduction . Accurate thermodynamic properties data and prediction

methods for mixtures of cryogenic fluids are needed to design and

optimize low temperature processes and equipment. This project provides

new experimental measurements on equilibrium properties and compilations

of evaluated equilibrium properties data which are suitable for direct

technological use or for the evaluation of prediction methods.

Objectives or Goals . The overall objectives of this project are to

provide critically evaluated data on the phase equilibria and thermodynamic properties of cryogenic fluid mixtures. The program has been

divided -into the follov/ing elements:

a) Preparation of a comprehensive bibliography on experimental

measurements of equilibrium properties for mixtures of selected

molecular species of principal interest in cryogenic technology.

b) Selection and/or development of methods for correlation, evaluation

and prediction of equilibrium properties data.

c) Retrieval and evaluation of experimental data for specific mixture

systems selected on the basis of theoretical and/or technological

importance.

d) Preparation of guidelines for future research based on the

deficiencies noted in (a) , (b) , and (c)

.

e) Performing experimental research to alleviate deficiencies and

provide a basis for improvement of prediction methods.

Background . A physical equilibria of mixtures research project was established in the Thermophysical Properties Division in 1959. The

initial effort, based on a bibliographic search and other considerations,

was directed toward the acquisition of new experimental data on the

solid-vapor and liquid-vapor equilibria and physical adsorption propertie:

for a limited number of binary and ternary mixtures of components with

widely separated critical temperatures. Most of the systems studied

included one of the light hydrocarbon species methane, ethane, or ethylene (ethene) -- with one of the quantum gases -- helium, hydrogen,

or neon. The data for these systems led to significant improvements in

the predictions of physical adsorption equilibrium and a correlation

for the prediction of deviations from the geometric mean rule for

combining characteristic energy parameters. In addition, significant

new information was obtained for interaction third virial coefficients

which was used in a correlation by one of our consultants, J. M.

Prausnitz. The approach taken in this work has been as fundamental as possible v/ith the intention of having an impact on a broad range of

mixture problems.

Recent efforts have been directed toward problems associated with

systems containing components with overlapping liquid temperature

ranges, such as nitrogen + methane, methane + ethane, etc.

10
7. Program and Results . The recent progress is summarized as follows:

a) During this period, reviews were received from the editor of the

Journal of Physical and Chemical Reference Data on the paper

discussing compilation, evaluation and correlation of liquid-vapor

equilibria data for the methane ethane system. As a result of

the comments of one of the three reviewers and one additional

question we felt should be answered, a thermodynamic consistency

text of each data set via the equal areas test was initiated and

a revision of the Barker method program was developed to correct for

vapor phase nonidealities with the Peng-Robinson equation of state

for comparison with one using the virial equation of state. The

results of these additional evaluations will be completed early

in the next reporting period and the manuscript will be revised

accordingly.

b) A compilation, evaluation, and correlation of the liquid-vapor

equilibria for the methane + propane system, similar to that for

methane + ethane, was initiated this period. As a result of our

experience with the methane + ethane system, and the reaction of

the reviewers, we expect the evaluation process to be simplified

somewhat

.

c) The papers discussing the excess volume model for predicting

orthobaric densities of LNG mixtures and the results of the

mixture molar volume measurements made at the University of

Wyoming will appear in the same issue of Fluid Phase Equilibria.

The complete citations are given in the ref erences .

^ 2 , 5)

8. Problem Areas . None.

9. Funding . January 1 - June 30, 1978.

Man-years expended

Equipment and/or Services Purchased

Total Reporting Period Cost

Balance Remaining

10- Future Plans . Objectives and Schedule: Quarter

Complete thermodynamic consistency

tests and comparison of values

for different equations of state

for methane + ethane. Revise

manuscript.

Compile, evaluate and correlate

liquid-vapor equilibria data for

methane + propane.

Prepare and report graphs of K-values

and equilibrium compositions for

methane + propane.

0.6

2. 2K$

48.5K$

15.7K$

11
References

1. M. J. Hiza, R. C. Miller, and A. J. Kidnay, A Review, Evaluation, and

Correlation of the Phase Equilibria, Heat of Mixing, and Change in

Volume on Mixing for Liquid Mixtures of Methane + Ethane, J. Phys. Chem.

Ref. Data (being revised for publication).

2. M. J. Hiza, An Empirical Excess Volume Model for Estimating Liquefied

Natural Gas Densities, Fluid Phase Equilibria 2^, No. 1, 27-38 (1978).

3. R. C. Miller and M. J. Hiza, Experimental Molar Volumes for Some

LNG-Related Saturated Liquid Mixtures, Fluid Phase Equilibria 2_, No. 1,

49-57 (1978).

12
1. Title . DENSITIES OF LIQUEFIED NATURAL GAS fUXTURES

Principal Investigators . W. M. Haynes, R. D. McCarty and M. J. Hiza

2. Cost Center Nixmbers . 7361574

3. Sponsor Project Identification . LNG Density Project Steering

Cominittee ; American Gas Association, Inc., Project BR-50-11.

4. Introduction . Accurate density measurements and calculational methods

for liquefied natural gas mixtures are needed to provide a basis for

custody transfer agreements and for mass, density, and heating value

gauging throughout the fuel gas industry.

The basis for the custody transfer of natural gas is its heating value.

It is difficult to determine and agree on the heating value of extremely

large volumes of natural gas in the liquid state. For example, methods

for calculating the heating value of a liquefied natural gas mixture

require knowing its density, which in turn depends on its composition,

tem.perature , and pressure. As the compositions of LNG mixtures vary

considerably, depending on the sources of the gas and the processing

conditions, accurate methods are needed for calculating liquid densities

at arbitrary compositions, temperatures and pressures. The accuracy is

important because of the extremely large volumes of liquid involved.

5. Objectives or Goals . The objectives of this v;ork are to perform

accurate (0.1%) and precise (0.02%) measurements of the densities of

saturated liquid methane, ethane, propane, butanes,, nitrogen and their

mixtures mainly in the temperature range 105 - 140 K, and to test and

optimize mathematical models for calculating the densities of LNG

mixtures at arbitrary compositions and temperatures.

6. Background . This project is being carried out at NBS because of the

realization that equitable custody transfer agreements could be reached

more readily if the density measurements and the evaluation and development of calculational methods v/ere performed by independent professionals.

An apparatus incorporating a magnetic suspension technique has been

developed for absolute density measurements on liquids and liquid

mixtures, particularly at saturation, for temperatures between 9 0 and

300 K. The estimated imprecision of measurement is less than 0.02%

and the estimated inaccuracy is less than 0.15%.

7 . Program and Results . 7.1 Measurements . During the past six months measurements have been

performed on the following mixtures:

0.85 CH. + 0.15 C^H^

4 2 6 0.93 CH^ + 0.07 nC^H^Q

0.85 CH. + 0.05 C^H, + 0.05 C,Ho + 0.05 iC.H,

„

4 2 6 3 8 4 10

0.920 CH. + 0.080 iC.H,,,

4 4 10

0.851 CH. + 0.058 C„H, + 0.048 C,H„ + 0.043 nC-H^-

4 2 5 3 o 4 10

0.859 CH. + 0.115 C^H, + 0.013 C,Ho + 0.005 iC.H,„ + 0.007 nC.H,^

4 26 38 4 10 4 10

0.860 CH^ + 0.046 C2Hg + 0.048 C^Hg + 0.046 iC^E^^

0.006 N-, + 0. 906 CH. + 0. 060 C^H, + 0.022 C^Hq + 0.003 iC.H, „ 2 4 26 38 4 10

+ 0.003 nC^H^Q

0.048 + 0. 809 CH. + 0.045 C-H, + 0.050 C,Ho + 0. 047 iC .H,

2 4 26 38 4 10

13
0.0060 N2 + 0.9007 CH^ + 0.0654 C^E^ + 0.0220 C^Hg + 0.0029 iC^H^^

+ 0. 0028 nC^H^Q + 0. 0001 iC^K-|^2 + 0-0001 '^^5^^12

0.846 CH. + 0.079 C„H, + 0.051 C-,H„ + 0.025 nC.H,-,

4 2 6 3 8 4 10

0.014 N2 + 0.859 CH^ + 0.085 C^^^ + 0.030 C^Hg + 0.005 iC^H^Q

+ 0.007 nC^Hj^Q

0.010 N2 + 0. 882 CH^ + 0.073 C^i^^ + 0.026 C^Hg +* 0.005 iC^H-^Q

+ 0.005 nC^H^Q

0.846 CH. + 0.082 C„H, + 0.048 C^Ho + 0.013 iC.H,„ + 0.013 nC.H,»

4 ZD 3o 4±U 41U

0.026 N2 + 0.812 CH^ + 0.085 €2^^ + 0.049 C^Hg + 0.027 nC^H^Q

0.9279 CH^ + 0.0721 nC^H^Q

0.783 CH^ + 0.217 iC^H^^Q

Except for the methane-isobutane binary mixtures, the discrepancies

between experimental densities and values predicted using the extended

corresponding states method were less than 0.1%.

The next mixtures to be investigated are as follows:

0.778 CH. + 0.222 nC.H,.

4 4 10

0.059 N2 + 0.891 CH^ + 0.050 nC^H^^

8-component mixture containing maximum of 0.5% pentanes

No mixture containing a significant amount of pentanes has been prepared

yet for several reasons. Since the mixture must be prepared in steps

using several different cylinders, we had to wait until sufficient

cylinders were available such that the measurement program would not be

interrupted. Also, we wanted time to carefully analyze the procedures

for the preparation of such mixtures. We must be sure that the mixture

is well characterized. It is expected that a mixture containing 0.5%

pentanes will be prepared and its density measured v/ithin the next

month.

7.2 Calculational Methods . No work on the four models has been done

during the reporting period ; however, they have been used extensively to

compare predicted and newly measured mixture densities. As noted

above in this report the disagreement between the densities calculated

from the extended corresponding states model and measured values has

been less than 0.1% except for two CH. - iC.H,Q mixtures where the

disagreement is from 0.1 to 0.2%.

Problem Areas . None.

Funding . January 1 - June 30, 1978.

Man-years expended 0.6

Equipment and/or Services Purchased 2.7K$

Total Reporting Period Cost 49.2K$

Balance Remaining 6.7K$

14
10. Future Plans . Objectives and Schedule: Quarter 3 4

Complete mixtures measurements.

Measure, analyze, and report

multicomponent mixture data,

including selected LNG-like

mixtures

.

Prepare final calculational

methods paper.

15
1. Title . PROGRAM FOR REDUCING THE COST OF LNG SHIP HULL CONSTRUCTION -- PHASE II SHIP STEEL IMPROVEMENT PROGRAM

Principal Investigators . H. I. McHenry, M. B. Kasen, and R. P. Reed

2 . Cost Center Number . 27534 30 - LNG Ship Hull Materials (Shipyard Contracts)

2751430 - LNG Ship Construction Materials (Metallurgical Evaluation)

2752430 - LNG Ship Hull Materials (Fracture Properties)

3. Sponsor Project Identification . Maritime Administration Misc. P. 0.

400-58073.

4. Introduction . Construction of LNG tankers requires the use of fine grain

normalized steels for the part of the hull structure that is cooled by

the cargo to temperatures in the range of 255 K (0°F) to 228 K (-50°F)

.

Several ABS steels have satisfactory base plate properties but extreme

care must be exercised during welding to avoid degradation of the steel

adjacent to weld (the heat affected zone) to a level of toughness below

U. S. Coast Guard requirements. Significant cost problems are being

encountered by U. S. shipyards due to the resulting inefficient low-heatinput welding procedures that must be employed to meet the fracture

requirements in the heat affected zone. The feasibility of reducing the cost of LNG ship hull construction was investigated in Phase I of this project, leading to the Phase II program

described below.

5. Obj ective . The objectives of the Phase II program are 1) to have the

four major plate producers supply three LNG shipyards with production

heats of ABS steels modified to possess improved transverse fracture

properties at low temperatures, 2) to have the LNG shipyards evaluate

these plates by qualifying optimum welding procedures in accordance with

the USCG requirements, and 3) to provide a metallurgical evaluation of

factors that influence heat affected zone toughness in the improved

steels.

6. Background . Early in 1974, the Welding Panel of MarAd ' s Ship Production

Committee recommended that a program be conducted to reduce the cost of

ship hull construction. NBS was requested by MarAd to propose such a program to the LNG subcommittee of the Welding Panel at a meeting in

Boulder in August. In mid-October, MarAd approved the initial phase of

NBS ' s recommended program, i.e., to survey the problem and the technology

available for its solution. On the basis of this survey and as the

result of a meeting of the Welding Panel in March, 1975, a coordinated

program involving the LNG shipyards, the steel suppliers, and NBS was recommended to MarAd and to the Welding Panel. This program was approved

and work started in May 197 5. Cost-sharing contracts for the evaluation

of the improved steels were awarded in 1975 to the three participating

shipyards: Avondale Shipyards, Inc., Newport News Shipbuilding and

Drydock Co. and General Dynamics-Quincy Shipbuilding Division. A similar

contract was signed with Lukens Steel Company to evaluate Cb-treated V051 steel with and without sulfide shape control. The three participating shipyards and Lukens Steel Co. completed the shipyard evaluation

phase of the program in 1977. The ABS steels with sulfide shape control

had excellent toughness and the HAZ toughness was improved, particularly

for shielded metal arc (SMA) and gas metal arc (GMA) welds. The most

promising results for high-heat-input welds were obtained with the Cbtreated V-051 steel with sulfide shape control.

Follow-on contracts were awarded to the three participating shipyards to

further evaluate the most promising ship steels: ABS grades V-051 (Cb,

SSC) , V-062 (SSC) , and V-062 (Cb, SSC)

.

16
7. Program and Results . During this reporting period, most of the work on

the follow-on contracts was completed. Six steels v;ere evaluated by one

or more shipyards as summarized below:

Steel Type Thickness (in) Source Shipyard Evaluation

V-062 (low S) 1/2, 1 Armco NNS

V-062 (SSC) 1/2, 1 Armco NNS, GD/Q

V-062 (Cb, low S) 1/2, 1 Armco GD/Q, AS

I

V-062 (Cb, SSC) 1/2, 1 Armco GD/Q, AS

I

V-051 (Cb, SSC) 1/2, 1 Lukens NNS, GD/Q, AS

I

C-Mn-Mo-Cb 1.2 Climax NNS, GD/Q

where: NNS - Newport News Shipbuilding, GD/Q - General Dynamics,

Quincy Shipbuilding Division, ASI - Avondale Shipyards, Inc.

The results of the NNS evaluation indicated that the V-062 (SSC) and the

V-051 (Cb, SSC) had satisfactory HAZ toughness at 222 K (-60°F) providing the weld metal toughness exceeded the 27 J (20 ft lb) requirement.

For three-wire SAW welds, the Armco W-18 weld metal with nominally 2% Ni was consistently below 27 J (20 ft lb) and consequently none of the welds

were qualified at 222 K (-60°F) . For single wire SAW welds, the Rayco

130 weld metal with nominally 1% Ni consistently exceeded 27 J (20 ft

lb) . In both the 1-wire and 3-wire SAW welds, the same heat input of

67 kJ/cm (161 Btu/in) was used for the final pass. These results indicate that further work on filler metal selection is needed to take

advantage of the improved heat input tolerance of the base metals. The

NNS tests also indicated that the C-Mn-Mo-Cb pipeline steel had very low

HAZ toughness.

The results of the GD/Q evaluation indicated that the V-062 (SSC) , V-062

(Cb, low S) , V-062 (Cb, SSC) and V-051 (Cb, SSC) steels generally had

satisfactory toughness at 222 K (-60°F)(228 K (-50°F) for V-062 (Cb,

SSC) , 1/2-inch thick) for SMA welds with 8018C-1 electrodes and for SAW

welds with Airco AX-90 wire. Exceptions were the 1/2 inch-thick V-062

(Cb, SSC) , SMA, vertical and v/elds made with a twin-wire single-arc

process. The GD/Q tests also indicate that the C-Mn-Mo-Cb pipeline steel

had very low HAZ toughness.

The results of the ASI investigation indicated that their choice of

filler metals resulted in weld metal and sometimes fusion line and 1 mm

toughness values that did not exceed 27 J (20 ft lb) at 222 K (-60°F) . The ASI filler metals were AWS E-9018-M electrodes for SMA welds and

Armco W-19 wire with Linde 709-S flux. ASI plans to conduct additional

tests on submerged arc weldments with Linde Ml-88 wire.

8. Problem Areas . Lov/ weld metal toughness, particularly in submerged arc

welds, is making it difficult to evaluate the V-062 and V-051 base plates.

9. Funding . January 1, 1978 to June 30, 1978

Cost Center Cost to 6/30/78 Balance

7363430 180K 0

7361430 71K 9K

7362430 64K 16K

10. Future Plans . Work should be completed on the follow-on testing program

(Phase II of the Ship Steel Improvement Program) this year. A proposal

will be submitted to MarAd to conduct additional tests on filler metals

for low temperature service.

17
Title . CUSTODY TRANSFER - LNG SHIPS

Principal Investigators . W. C. Haight, R. J. Hocken, B. R. Borchardt/

R. G. Hartsock, R. C. Veale, J. D. Siegwarth, J. F. LaBrecque, and C. L.

Carroll

Cost Center Numbers . 7360460, 7361575, 7362575, 7363575, 7310570,

7310571

Sponsor Project Identification . LNG Custody Transfer Measurements Supervisory Committee and Maritime Administration Misc. P.O. #400-79005.

Introduction . In response to the requests from the U.S. shipbuilding

industry, NHS is independently examining the accuracies of LNG tank cargo

capacity tables and developing alternative survey techniques.

Ob j ectives . The objectives of the program are to develop new techniques

for LNG transport tank calibration and to test the accuracy of present

calibration techniques as part of an overall study of custody transfer

methods aimed at increasing the accuracy of custody transfer measurements

Background . Initial funding by the Maritime Administration (7360460)

supported some preliminary tests of calibration of spherical LNG ship

tanks. As a result of these measurements, the LNG Custody Transfer

Supervisory Committee and the Maritime Administration have funded extension of the v;ork to the membrane tanks and the free standing prismatic

tanks now under construction in U.S. shipyards.

Program . Techniques for accurately dimensioning prismatic tanks of the

membrane type have been developed by the Macrometrology Group at NBS

The technique requires establishing a model of a solid of the same shape

as the tank just inside the tank walls using laser planes. Distances

from the laser planes to the wall are measured at a larger number of poin

The size and shape of the solid defined by the laser planes is measured

by a multiple redundant method so the accuracy of the measurement of the

dimensions of the solid can also be determined. This technique has been

applied to four membrane tanks. Abbreviated surveys have been completed

on five additional tanks.

Two of the free standing prismatic tanks have been tested for distortions

resulting from lifting and loading them onto the ships. The distortion

detected was not significant relative to the accuracy required of the

photogrammetric survey.

The accuracy and precision of the photogrammetric tank survey method is

being tested v/ith length standards. Invar tapes are being employed

to give accurate target separations for test lengths near the maximum

dimensions of the tank. Of the tanks thus far tested, the accuracy and

precision of the photogrammetric measurements of the test target separations indicate this survey technique meets volume accuracy requirements.

Problem Areas . None.

Funding . January 1 - June 30, 1978.

Man years expended 1.2

Total reporting period cost $172. Ok

Balance remaining $113. Ok

Future Plans . Complete the surveys of the membrane tanks and compare

the resulting tank capacities with the capacities determined by the primary survey contractor when the latter become available. The laser plane

dimensioning technique will be modified to check the capacity of one of

the free standing prismatic tanks and to examine hydrostatic distortion

effects. Additional test tape measurements are planned for subsequent

tanks to look for possible survey distortions and to examine horizontal

and vertical calibration factors.

18
1. Title. HEATING VALUE OF FLOWING LN6

Principal Investigators . J. A. Brennan

2. Cost Center Number . 7366579

3. Sponsor Project Identification . Pipeline Research Committee (American

Gas Association) PR-50-48.

4. Introduction . This project will test instrumentation for making heating

value measurements on flowing LNG in actual applications. Information

from projects currently underway by Siegwarth (cost center 7367574) on densimeters, by Haynes and Hiza (cost center 7361574) on mixture

densities and by Parrish (cost center 7360575) on LNG sampling will be

utilized where appropriate to provide state of the art information.

5. Objectives . The objective of this project is to measure total heating

value of LNG flowing in a pipeline by the integration of individual

measurements of flow, density and specific heating value. Flov/ measurement requires determination of flowmeter performance in line sizes

larger than presently available calibration facilities. Therefore, a secondary objective is to establish appropriate flowmeter scaling laws.

6. Background . The LNG flow facility at NBS was used to evaluate the re- sponse and the integration of the individual elements of the heating

value measurement. Different compositions of LNG were tested to provide

a range of densities and temperatures sufficient to. determine any dependencies. Sampling work was combined with the sampling project (cost

center 7 360575) to better define the important criteria of this phase

of the measurement problem.

Flowmeter scaling work utilizes the cryogenic and water flow facilities

at NBS as well as private LNG peak shaving and import facilities.

7. Program and Results . All test instrumentation for the Southern Energy

Import Terminal has been installed and the recording equipment connected.

The first shipload of LNG arrived during June 1978 but no testing will

be attempted until after the terminal has been completely checked out.

It will probably be possible to start the actual testing during the third

or early fourth quarter of 1978.

8. P roblem Areas . The delays in receiving the instrumentation, which was described in the last report, precluded performing all the desired tests

in liquid nitrogen before shipment to Southern Energy. Sufficient tests

were run to detect equipment failure but not enough to establish overall

performance

.

9. Funding . January 1 - June 30, 1978.

Man-years expended .2

Total reporting period costs $8k

Balance remaining $22k

10. Future Plans . LNG flow tests will be run when appropriate, consistent

with the start-up of the terminal.

19
1. Title . LNG DENSITY REFERENCE SYSTEfl

Principal Investigators . J. D. Siegwarth and J. F. LaBrecque

2. Cost Center Number . 7367574

3. Sponsor Project Identification . American Gas Association, Inc.,

Project BR-50-10; National Bureau of Standards, Gas Research Institute.

4. Introduction . A density reference system has been developed to evaluate

the ability of commercially available instruments to measure densities

of LNG directly. Density is an essential measurement in determining the

total energy content of natural gas reservoirs.

5. Obj ectives . The object of this research is to develop and supply adequate calibration methods and calibration standards to densimeter manu- facturers and users for providing traceability of accuracy to field

density measurement systems.

6. Background . The density reference system project was initiated in 1973.

Since that time the reference system has been designed, constructed, and

is now in operation, evaluating commercial density metering systems.

Reports describing the density reference system and the results of the

tests of four commercial densimeters have been published. These reports

are

Siegwarth, J. D. , Younglove, B. A. and LaBrecque, J. F., Cryogenic fluids

density reference system: provisional accuracy statement, Nat. Bur.

Stand. (U.S.) Tech. Note 698, 24 pages (1977), and

Siegwarth, J. D., Younglove, B. A. and LaBrecque, J. F., An evaluation

of commercial densimeters for use in LNG, Nat. Bur. Stand. (U.S.) Tech.

Note 697, 43 pages (1977).

7. Program and Results . The DRS has been operated with liquid nitrogen

fillings several times in the course of. testing seven additional Archimedes densimeters. These measurements have not established the accuracy

of the DRS as a density standard in liquid nitrogen yet because the temperature was only measured once and the purity of the LNz sample was only

controlled for that one measurement.

Tests of the seven Archimedes densimeters in methane and LNG-like mixtures have shown that the accuracy of these densimeters is poorer than

indicated by the tests reported in Technical Note 697. This reduced

accuracy may result because the instrument calibration is based on mea- surement in fluids of density and boiling temperature well removed from

the density and boiling temperature of LNG. The fault or faults of the

densimeter system resulting in reduced accuracy have not yet been positively identified.

During the course of these tests, modifications of and adjustments to the

density reference system have improved its performance. The AT in the

sample holder is now always below 40 mK and is rarely larger than 20 mK.

This reduced AT and the addition of pneumatic actuaters to the weight

changing mechanism of the DRS densimeter has reduced the 1 a scatter of

the density measurements well below 0.01%.

Some preliminary redesign work of the sample container is underway. The

redesigned sample container will be larger in size and will permit insertion of the densimeters for test without disturbing the insulating

vacuum. This design will allow tests of various types and numbers of

densimeters with only minor modifications to the DRS.

8. Problem Areas . The recent densimeter tests have shown that LN2 is not

the best choice of a calibration fluid for densimeters to be used in LNG.

Better calibration techniques for commercial instruments are needed.

20
Funding . January 1 - June 20, 1978.

Man years expended

Total reporting period cost

Balance remaining

0.2

$12. Ok

$48. Ok

Future Plans . The capacity and flexibility of the DRS will be increased.

With the addition of a separate sample storage dewar, changing the densimeters under calibration will be rapid and the system can be demonstrated

as a commercially practical calibration system. A transfer standard will

be sent to Gaz de France, Paris when the calibration problems with the

Archimedes densimeter are solved. A recent entry to the cryogenic densimeter market has been made available for testing. This instrument is

a vibrating cylinder type.

21
1. Title . LNG SAMPLING MEASUREMENT STUDY

Principal Investigators . W. R. Parrish, R. J. Richards and J. F. LaBrecque,

2. Cost Center Numbers . 7365574.

3. Sponsor Project Identification . A. G. A. -PRC LNG Supervisory Committee.

4. Introduction . Composition is used to determine both the heating value

and the quantity (through density) of LNG shipments. Thus, any error

in composition doubles when calculating the total heating value and

dollar value of a LNG tanker cargo. Compositions are determined by

sampling LNG, on either a batch or continuous basis, and analyzing the

vaporized mixture. Although several sampling techniques exist, none

have received v/idespread acceptance in the LNG industry. Also, a standard technique has not been established for analyzing the vaporized

sample.

5. Objectives or Goals . The objectives of this work are the same as the

last reporting period with emphasis on vaporizer and accumulator design.

6. Background . This work v/as performed because there is a need to

determine the best means for obtaining the composition of LNG shipments. Current LNG buying contracts include specifications on when and

how many liquid samples are to be taken but omit the sampling technique

to be used. The evaluation of sampling techniques by NBS is expected to

lead to the acceptance of the most accurate composition determination

method by all parties involved in LNG custody transfer.

7. Program . Based on the previous work, the two factors preventing development of a general design are sampling rate and vaporizer-accumulator

design. Test results showed that the precision of the system diminishes

below a certain sampling rate. Attempts to correlate sampling rate with

the limited range tested for the other variables failed. However, by

process of elimination, the most likely factors causing the effect of

sampling rate on precision are probe size, line size between the probe

and vaporizer and heat leak. All of these variables are being evaluated

in a laboratory apparatus, where the operating variables are controlled

closely and mixtures of known composition are used.

Laboratory tests demonstrated that, if a simple tube vaporizer is used, an accumulator must be used. This is because fractionation occurs during

vaporization and the accumulator volume provides time for the sample to

become homogenized again. Laboratory tests indicated that the field system required a larger accumulator than would be expected from laboratory

results. However, the accumulator residence time should be minimized to

insure adequate mixing and maintain a reasonable response time. Therefore, this project is considering two v/ays to eliminate the need for the

accumulator. The first method is to place a static mixing device just

downstram of the tube vaporizer. If the poorly mixed gas from the vaporizer is not in plug flow, this mixer may remix the components. However,

it will have no effect if the stream is in plug flow. The second method

places the static mixing device in the vaporizer. Here the device provides both mixing during vaporization and additional heat transfer sur- face area. (Previous tests indicated that sampling precision is better

when the sample is vaporized quickly.)

8. Problem Areas. None.

22
9. Funding . January 1 - June 30, 1978.

Man-years expended

Total reporting period cost

Balance remaining

.2

$20 . 3k

$54. 7k

10. Future Plans . The work under cost center 7360575 is complete. However, additional work is being supported by the Pipeline Research

CoiTuTiittee , A.G.A., to improve the sample vaporizer design (NBS cost

center 7365574). After finishing the laboratory tests, field tests

will be made at a yet-to-be-determined site.

23
1. Title . SURVEY OF CURRENT LITERATURE ON LN6 AND METHANE

Principal Investigator . Neil A. Olien

2. Cost Center Number . 7369574

3. Sponsor Project Identification . Gas Research Institute Grant No.

5010-362-0019 and American Gas Association, Inc., Project BR-50-10.

4. Introduction . It is important that all NBS personnel working in LNG, as well as the AGA and others, keep up with what is going on throughout the

world in the LNG field. This project is designed to provide the Current

Awareness and other information services to allow workers to keep

abreast of new research and other developments.

5. Objectives or Goals . We will publish and distribute each April, July,

October, and January a listing of all significant papers, reports, and

patents relating to methane and LNG properties and technology. The

references will be listed under convenient subject headings. The

Quarterly will be distributed to all interested AGA member companies and

be made available to the general public on a subscription basis. In

addition, LNG related information will be entered into the Cryogenic

Data Center's Information System for quick retrieval. A continuing

awareness of the current publication scene is maintained for any new

periodicals to be reviewed cover-to-cover. Finally we will update and

make available comprehensive bibliographies on the properties and

technology of LNG. There are four bibliographies involved: methane

properties, methane mixtures properties, processes and equipment

involving methane and LNG, and patents relating to methane and LNG

technology. These four will be updated annually.

6. Background . In 1969 we made a thorough review of the world's publications to determine which periodicals and abstracting services should be

scanned cover-to-cover to adequately encompass the LNG field. The

result is that we now scan over 330 primary publications and nearly 25

secondary publications. Of these, approximately one-third are directly

related to LNG. In addition, we have increased our coverage of the

energy field to include hydrogen as a future fuel. Much of this

information is also pertinent to LNG and as such is listed in our LNG~related publications. Our Current Awareness Service has been

published weekly since 1964 (beginning in 1975 the publication became

biweekly) and the Liquefied Natural Gas Survey has been published

quarterly since 1970.

7. Program and Results . Four issues of the LNG Quarterly are prepared each

year and distributed. There are now 117 subscriptions going to AGA

Member Companies and 161 to other subscribers.

The four comprehensive bibliographies mentioned in section 5 have been

reviewed and shortened, and more selective bibliographies have resulted.

The latest versions were completed as of January 21, 1977.

B-1525 THE THERMOPHYSICAL PROPERTIES OF METHANE AND DEUTERO-METHANE

IN THE SOLID, LIQUID AND GASEOUS PHASES - A SELECTED BIBLIOGRAPHY. Indexed by property, phase and author, 100 pages

(Jan 1977) . ($10. 00)

B-1526 THE THERMOPHYSICAL PROPERTIES OF METHANE MIXTURES - A

SELECTED BIBLIOGRAPHY. Indexed by property, system and

author, 166 pages (Jan 1977). ($15.00).

B-1524 PROCESSES AND EQUIPMENT INVOLVING LIQUEFIED NATURAL GAS AND

METHANE - A SELECTED BIBLIOGRAPHY. Indexed by subject and

author, 285 pages (Jan 1977). ($25.00).

24
B-152 7 PATENTS RELATING TO METHANE AND LNG TECHNOLOGY - A SELECTED

BIBLIOGRAPHY. Indexed by author, 150 pages (Jan 1977).

($15. 00) . Over the past seven years we have distributed over 500 copies of these

and the comprehensive bibliographies.

The size of these has grown to the extent that their usefulness is

limited, therefore it was decided that they would not be updated and a series of more specialized bibliographies would be made available. The

following list gives those currently available. Additional topics will

be added as necessary.

B-152 8 LIQUEFIED NATURAL GAS STORAGE INCLUDING INSULATION SYSTEMS.

1181 references, indexed by author and subject, 210 pages

($20.00).

B-152 9 LIQUEFIED NATURAL GAS PEAKSHAVING AND SATELLITE OPERATIONS.

221 references, indexed by author, 36 pages ($10.00).

B-1530 LIQUEFIED NATURAL GAS STRATIFICATION AND ROLLOVER. 38 references, indexed by author and subject, 10 pages ($5.00).

. B-1531 LIQUEFIED NATURAL GAS SAFETY INCLUDING SPILLS. 368 references

indexed by author and subject, 72 pages ($10.00).

B-1532 LIQUEFIED NATURAL GAS PIPELINES AND TRANSFER LINES. 226

references, indexed by author, 44 pages ($10.00).

B-1533 LIQUEFIED NATURAL GAS SHIPS, BARGES AND OVERWATER TRANSPORTATION. 805 references, indexed by author, 138 pages ($15.00)

B-1534 LIQUEFIED NATURAL GAS VAPORIZORS INCLUDING COLD UTILIZATION.

330 references, indexed by author and subject, 58 pages

($10.00).

B-1535 LIQUEFIED NATURAL GAS HEAT TRANSFER. 155 references, indexed

by author, 34 pages ($10.00).

B-1536 LIQUEFIED NATURAL GAS LIQUEFACTION AND REFRIGERATION. 551

references, indexed by author, 94 pages ($15.00).

B-1537 LIQUEFIED NATURAL GAS ECONOMIC FACTORS. 470 references,

indexed by author, 84 pages ($15.00).

B-1538 LIQUEFIED NATURAL GAS OVERLAND TRANSPORTATION. 76 references,

indexed by author, 15 pages ($5.00).

B-1539 LIQUEFIED NATUPsAL GAS PATENTS. 747 references, indexed by

author and subject, 119 pages ($15.00).

B-154 0 LIQUEFIED NATURAL GAS INSTRUMENTATION. 8 5 references, indexed

by author and subject, 23 pages ($5.00).

Problem Are^s, None.

25
9. Funding . January 1 - June 30, 1978.

Labor 6.8K$

Other Costs 1. 6K$

Total 8.4K$

Remaining 7.2K$

10. Future Plans . Issue 78-2 was delivered to the printer the second week

of July and should be distributed before the end of July.

26
1. Title . LIQUEFIED NATURAL GAS TECHNOLOGY TRANSFER

Principal Investigators . Dwain E. Diller, H. M. Ledbetter, and N. A.

Olien

2. Cost Centers . 7360403, 7361403, 7360570, 73G4574, 7368574, 7360127,

7360461, 7360594

3. Sponsor Project Identification . Maritime Administration, Miscellaneous

Purchase Order No. 400-79005; American Gas Association, Inc. Project

BR 50-10; Gas Research Institute; American Bureau of Shipping; NBS

Office of Standard Reference Data.

4. Introduction . The liquefied natural gas program at the Thermophysical

Properties Division of NBS Boulder represents an investment by

industry and government agencies of over $5 million over the past six

years. This investment was designed to develop reference quality

properties data for both fluids and materials and instrumentation and

measurement technology for the use of the LNG and related industries.

Information developed under this program must be transmitted to the

ultimate user in a timely and useful format. The classical publication

methods of NBS most certainly provide the scientist and research

engineer information in a form nost useful to the academic or near

academic community. However, as a result of extensive assessments of user requirements, it was found that an additional effective mode for

technology transfer would be an LNG Materials and Fluids User's Manual.

A complete outline and planned table of contents have appeared in

previous semiannual reports. The Maritime Administration of the

Department of Commerce and the 7\merican Bureau of Shipping have agreed

to sponsor the first year's efforts on the materials section, and the

American Gas Association, Inc. and the NBS Office of Standard Reference

Data haye agreed to sponsor the section on fluids and fluid mixtures.

The project was begun on April 1, 1976.

5. Ob j ectives . The Liquefied Natural Gas Materials and Fluids User's Manual

will provide a method of quick dissemination of property data and related

information for the effective generation, utilization and transportation

of LNG, The object is to improve technology transfer from the current

NBS Thermophysical Properties Division LNG physical measurements program

to the users, including federal agencies, the states and industry. For

the purpose of this data book, liquefied natural gas is defined as a cryogenic mixture (at less than approximately 150 K) of hydrocarbons,

predominantly methane, with less than a total of 20% of the minor

components ethane, propane, iso and normal butane, and nitrogen as an inert contaminant. LNG materials will be those associated with the

liquefaction, transport and storage of liquefied natural gas.

6. Background . The User's Manual is only one of a number of information

dissemination methods used to provide workers in the liquefied natural

gas (LNG) industry with properties data of known quality in a format

consistent with the requirements of the intended user. In the case of

the LNG User's Manual the intended audience is the field engineer, plant

manager, ship designer or process engineer interested in a ready reference of assessed quality for data to be used in conceptual design,

process monitoring, process analysis, and intercomparisons where precision

and accuracy are secondary to specific problem solutions. The hierarchy

of accuracy and precision will be defined and traceable through

references to scientific and engineering literature.

Data are classified into three groups by the NBS Thermophysical

Properties Division,

Group 1 . Data which have been generated experimentally by NBS, or have

been assessed, evaluated or experimentally verified by NBS.

27
Group 2 . Data which have been assessed and evaluated by NBS.

Group 3 . Data available in the scientific engineering literature

through the NBS Cryogenic Data Center or elsewhere. No NBS evaluation

or assessment has been made at this date.

In general, most data included in the LNG user's manual will be from

groups 1 and 2. Few new assessments or correlations are anticipated

or required for this work.

Data will be presented primarily in graphical form. Tables and analytical expressions will be used only where absolutely necessary. Graphs

and charts will be in loose-leaf form for ease of updating and additions.

This form will also allow immediate implementation for data already

available under the NBS LNG program and will provide a convenient format

for the output of data from existing projects. The user's manual will

not be a substitute for traditional publications in the scientific

literature where measurement science, technique, precision and accuracy

are paramount, but will provide the data and references for the necessary

assessment by the user. The publication of both graphical and tabular data will be in a dual

system of physical units. These units will be the traditional LNG

industry British System of BTU, pound, degree Fahrenheit and the SI

system of joule, kilogram and kelvin. It is the intent to give equal

weight to each system of units.

7. Program and Results . The first edition of the User's Manual became

available for distribution in September 1977. A complete description

and ordering information are included as part of this report. About

450 copies have now been distributed to sponsors and purchasers. New

orders are currently coming in at the rate of about ten per week.

All materials to be included in the first supplement to the User's

Manual have been sent to the printer. The first supplement will contain

31 graphs of revised updated and nev/ material on the properties of

structural metals and alloys (aluminums, nickel steels and stainless

steels); 40 graphs on thermal insulations (polystyrene foams, polyurethane foams, polyvinyl chloride foams, balsa, perlite, cellular glass

and glass fiber) ; 15 graphs and 3 wall charts on pure LNG components

(ethane) ; and 9 sheets on binary and multicomponent mixtures of LNG

components. The first supplement will also contain 46 pages of materials

specification tables and 38 pages of additional narrative and other

descriptive materials. The first supplement is expected to be ready

for distribution by late August 1978.

8. Problem Areas. None.

9. Funding. January 1 - June 30, 1978.

Labor - man-years expended 1.2

Funds expended 81.6K$

Balance remaining (first supplement) 0.0K$

Balance remaining (second supplement) 60.7K$

10. Future Plans . Work on the second supplement is in progress. Propane

graphs and thermodynamic property charts are being prepared. Additional

• graphs on mixtures of LNG components have been scheduled. Graphs on the properties of structural composites and aggregates (with emphasis

on concretes) have been proposed. No additional supplements are planned at this time.

28
LNG MATERIALS AND FLUIDS

A USER'S MANUAL OF PROPERTY DATA IN GRAPHIC FORiMAT

The National Bureau of Standards Cryogenics Division is distributing a loose-leaf LNG Materials and

Fluids User's Manual. The User's Manual is designed to provide property data and related information for the effective generation, utilization and transport of LNG.

The total edition is planned to include: — pure fluids data on methane, nitrogen, ethane, propane and iso and normal butane, — fluid mixtures data involving methane with nitrogen, ethane, propane and iso and normal

butane, including commercial LNG compositions, — LNG materials data on structural metals and alloys, and — materials data on thcnnal insulations, joining compounds, structural composite materials and aggregates, polymeric materials, and miscellaneous non-structural materials.

The first edition and expandable binder contains 138 two-color {8V2 x 1 l-inch) charts and six wall charts (22 x 34-inch). This edition's property data are pressure-density-temperaiure, th.ermodynamic, transport and electromagnetic properties of pure methane and nitrogen; fluid mixtures of methane with nitrogen; and, the elastic, thermal and mechanical properties of aluminum alloys

(3003, 5083 and 6061). stainless steels (304, 304L, 310 and 316), nickel steels (2.25. 3.5, 5 and 9%

nickel) and invar. The wail charts are of the thermodynamic properties enthalpy-entropy (H-S),

pressure-enthalpy (P-H) and temperature-entropy (T-S) for pure methane and pure nitrogen.

Both British and SI (International System) units are used throughout, easily discernable by printing

in separate colors.

The expandable binder allows for future supplements. Purchasers of the first edition will be notified upon completion of addtitiona! supplements and their respective prices. All charts are printed on a high wet strength lithographic map paper designed for a strong durable life.

Copies of the first edition S35 each and additional rolled wall charts C'^ SI each may be obtained

by forwarding the order form below with payment. For additional information contact LNG

Materials and Fluids; National Bureau of Standards; Cryogenics Division; 325 Broadway; Boulder,

Colorado 80302.

ORDER FORM QUANTITY PRICE

First Edition LNG Materials and Fluids User's Manual (P-' S35 ea. Additional Rolled 22 x 34 Charts: Nitrogen thermodynamic data Enthalpy-entropy wall chart (H-S) C'' S 1 ea. Pressure-enthalpy wall chart (P-H) (S S 1 ea. . Temperature-entropy wall chart (T-S) S 1 ea. Methane thermodynamic data Enthalpy-entropy wall chart ( H-S) ^' S lea.

Pressure-enthalpy wall chart (P-H) lea.

Temperature-entropy wall chart (T-S) ^ S 1 ea. . TOTAL

Mail form and remittance to: LNG Materials and Fluids; National Bureau of Standards; Cryogenics Division; 325 Broadway;

Boulder, Colorado 80302. 29
Title . OIML JOINT SECRETARIAT ON LNG MEASUREMENTS

Principal Investigators . Douglas Mann and James A. Brennan, NBS and

T. L. Hillburn, Phillips Petroleum Company.

Cost Center Number . 7361104

Sponsor Project Identification . Aip.erican Gas Association, Inc.,

NBS-Office of International Standards; and NBS.

Introduction . The liquefied natural gas program of the National Bureau

of Standards Cryogenics Division has, over the past five years, provided

the gas industry and interested Government agencies v/ith properties data

on materials and fluids, instrumentation, and measurement assistance in

the support of commerce in this significant and growing segment of the

supplementary fossil energy supply. Support of this program by the

American Gas Association, Inc. and Federal Government agencies such as the Maritime Administration (MarAd) , NASA, GSA, Fed6:ral Pov/er Commission

and the NBS-Office of Standard Reference Data has provided a ba<;is for

the national acceptance of the results of the NBS LNG program. Through

the U.S. -membership in the International Organization of Legal Metrology

there exists, at the present time, an opportunity to extend, internationally, the utility of data and measurement practice developed under

our joint Government/industry program. We have been requested (by OIML

membership) to establish an LNG Measurement Secretariat within OIML which,

if implemented, Vv-ould provide a significant international forum for the

results of our joint work. It is believed that a joint Secretariat with

the LNG industry would provide the most effective means of accomplishing

these objectives.

Obj ectives or Goals . Our objective is to accomplish the following goals

within the next three years.

a) To establish U.S. (NBS) thermophysical properties data for LNG as the standard data in international usage.

b) To establish U.S. (NBS) materials property data used in fabrication

and construction of LNG facilities (liquefiers, storage, transport) as the standard data in international usage.

c) To establish U.S. (NBS) approved measurement technology and • instrumentation as related to LNG (pressure, temperature, density, liquid

level, flov/) as the standard in international LNG trade. The precedent

has been established with the successful completion of the joint NBS-CGA

cryogenic flow measurement program which has resulted in the adoption of

a cryogenic flow measurement code by the National Conference on VJeights

and Measures. We wish to extend this code on an international basis.

d) To establish and maintain the leadership of U.S. science, engineering,

and industry in the research, technology, manufacture and marketing of

instruments and measurement systems for liquefied natural gas.

Background . OIML was founded in 19 5 5 to promote intergovernmental

cooperation in the field of legal metrology which relates to the com- patibility of standards of measurement and the legislation and government

regulations which m.ay affect such standards of measurement. OIML

recommends uniform international requirements for scientific and measurement instruments used in industry and commerce and works out model laws

and regulations for consideration by member nations; and, in addition, serves as a center of documentation and information exchange in legal

metrology. At present 43 nations are members of this intergovernmental

organization

The United States joined OIML in 1972 (the Senate by resolution of

August 11, 1972 gave its advice and consent to the accession of the U.S.

to the convention establishing OIML) . The responsibility for managing

U.S. participation in OIML was assigned to the Department of Commerce

30
and has since been delegated by the Department to the National Bureau of

Standards (NBS) . Under the general guidance of the Department of State

and the Secretary of Commerce, NBS is directly responsible for formulating and implementing U.S. policy towards OIML. U. S. participation in

the organization is deemed important for two reasons: First, to protect

and enhance some $1 billion worth of scientific and measurement instruments

exported each year by U. S. firms and to ensure equity in the trade of

commodities measured by these instruments; and second, to maintain the

U.S. as the world leader in the field of metrology.

In the spring of 1975 at a meeting in Paris of the International Committee

of Legal Metrology, the French and U.S. representatives discussed the

possibility of creating a new Reporting Secretariat No. 13 on "Liquefied

Natural Gas (LNG) Measurement". The U. S. representative, W. E. Andrus,

Jr. of NBS, agreed to explore the possibility with U. S. industry and

interested government agencies. These discussions resulted in a decision

to propose a joint Secretariat with the American Gas Association and

NBS-Cryogenics Division in order to best accomplish the tasks. These

conclusions were reached during several meetings extending through the

latter part of 1975 and early 1976. During the summer of 1977, representatives of NBS met with PTB (West Germany) and SIM (France) to discuss the proposed scope and to explore expansion of the effort to include

cryogenic fluids in general. Results of those discussions indicate some resistance to including different physical measurements (flow, density,

etc.) under a single recommendation for a specific group of fluids.

The proposed plan and scope were presented at the meeting of The Advisory

Committee for International Legal Metrology held at NBS-Boulder in September. The committee encouraged NBS to proceed with the present scope

and to continue to explore the possible inclusion of other cryogenic

fluids

7. Program and Results . A revised work plan for cryogenic fluids was generated by the technical associates Douglas Mann of NBS and T. L. Hillburn

of the Phillips Petroleum Co. representing A.G.A. and API. The scope of

the work plan included instrumentation and procedures for the custody

transfer measurements of pressure, temperature, density, liquid level,

flow and calorific value of liquefied atmospheric and natural (hydrocarbon) gases having pure fluid or mixture normal boiling points of

less than 150 K, Recommendations v/ill be limited to establishing total mass and, where applicable, total heating value. Fluids and fluid mixtures considered will be limited to commercially important liquefied

atmospheric gases, oxygen, nitrogen and argon and the primary components

of liquefied natural gas, methane, ethane, propane, iso- and normal

butane and pentane.

The draft work plan is presently under review by the OIML membership and

other interested parties. Comments on the plan and an expression of

interest as to formation of the first working group are being solicited.

8. Problem Areas . None.

9. Funding . January 1, 1978 - June 30, 1978.

Labor - Man-years expended 0.1

Funds expended 11.0K$

Balance remaining 4 . 0K$

10. Future Plans . Flow measurement of pure cryogenic fluids will be the first

of the recommendations generated under the proposed work plan. This will

be accomplished by combining the existing U.S. and European codes for flow

measurements. A working group will be formed of interested parties and

the first draft of this recommendation should be ready for review by

January of 1979.

31
BIBLIOGRAPHY

NBS Reports and Publications Related to LNG Technology

Which Have Appeared Since January 1977

1. Goodwin, R. D. , "Provisional thermodynamic functions for propane from

85 to 700 K at pressures to 700 bar," Nat. Bur. Stand. (U.S.),

Interagency Report 77-860 (Jul 1977).

2. Goodwin, R. D. , "Specific heats of saturated and compressed liquid

propane," J. Res. Nat. Bur. Stand. (U.S.) (in press, 1978).

3. Goodwin, R. D. , "On the non-analytic equation of state for propane,"

Adv. Cryog. Eng. _23 , 611 (1978).

4. Tsumura, R. and Straty, G. C. , "Speed of sound in saturated and

compressed fluid ethane," Cryogenics 193 (1977).

5. Haynes,'W. M. and Hiza, M. J., "Measurements of the orthobaric liquid

densities of methane, ethane, propane, isobutane and normal butane,"

J. Chem. Thermodynamics 9^, 179 (1977 ).

6. Hiza, M. J., Haynes, W. M. and Parrish, W. R. , "Orthobaric liquid

densities and excess volumes for binary mixtures of lov/ molar mass alkanes and nitrogen between 105 and 140 K," J. Chem. Thermodynamics

9, 873 (1977)

7. Hiza, M. J. and Haynes, W. M. , "Liquid mixture excess volumes and total

vapor pressures using a magnetic suspension densimeter with compositions

determined by chromatographic analysis: methane + ethane," in Advances

in Cryogenic Engineering, Volume 23 (Plenum, New York, 1978), p. 594.

8. Haynes, W. M. , Hiza, M. J. and McCarty, R. D. , "Densities of LNG for

custody transfer," Proceedings of LNG-5 Conference, Dusseldorf, Germany

(Aug 1977 ) .

9. McCarty, R. D. , "Comparison of mathematical models for the prediction

of LNG densities," Nat. Bur. Stand. (U.S.), Interagency Report 77-867

(Oct 1977) .

IC. Diller, D. E., "LNG density determination," Hydrocarbon Proc. 5_6, No. 4,

142 (Apr 1977)

11. Hiza, M. J., "An empirical excess volume model for estimating liquefied

natural gas densities," Fluid Phase Equilibria 2, 27 (1978).

12. Miller, R. C. and Hiza, M. J., "Experimental molar volumes for some LNG-related saturated liquid mixtures," Fluid Phase Equilibria 2^, 49

(1978)

13. Miller, R. C, Kidnay, A. J. and Hiza, M. J., "Liquid-vapor equilibria

in the methane + ethene and methane + ethane systems from 150 to 190 K,"

J. Chem. Thermodynamics 9, No. 2, 167 (Feb 1977).

14. Hiza, M. J., Miller, R. C. and Kidnay, A. J., "A review, evaluation,

and correlation of the phase equilibria, heat of mixing, and change in

volume on mixing for liquid mixtures of methane + ethane," J. Phys

Chem. Ref. Data (to be submitted).

15. Hanley, H. J. M. , Haynes, W. M. and McCarty, R. D. , "Viscosity and

thermal conductivity coefficients for dense gaseous and liquid methane,"

J. Phys. Chem. Ref. Data 6^, 597 (1977).

32
16. Hanley, H. J. m. , Gubbins, K. E, and Murad, S., "A correlation of the

existing viscosity and thermal conductivity data of gaseous and liquid

ethane," J. Phys. Chem. Ref. Data 6, 1167 (1977).

17. Hanley, H. J. M., Holland, P. M. , Gubbins, K. E. and Haile, J. M.

,

"A correlation of the viscosity and thermal conductivity data for

gaseous and liquid propane," J. Phys. Chem. Ref. Data (in press).

18. Hanley, H. J. M. , "Prediction of the thermal conductivity of fluid

mixtures," Proceedings 7th ASME Conf. on Thermophysical Properties;

Hanley, H. J. M. in Phase Equilibria and Fluid Properties in the

Chemical Industry , ACS Symp. Series No. 60 (1977).

19. Hanley, H. J. M. , "Transport coefficients in the one-fluid approximation

behavior in the critical region," J. Res. Nat. Bur. Stand. (U.S.) 82 , 18 (1977).

20. Ackerson, B. J. and Hanley, H. J. M. , "The thermal diffusivity of

methane in the critical region," Chem. Phys. Letters 53^, 596 (1978 ).

21. Ackerson, B. J. and Straty, G. C, "Rayleigh scattering from methane,"

J. Chem. Phys. (in press, 1978),

22. Mann, D. B., editor, "LNG materials and fluids user's manual," (Sep

1977), available from the National Bureau of Standards, Boulder, CO

80303.

23. Diller, D. E., "NBS research on LNG thermophysical properties data and

custody transfer measurement miethods," Proceedings of Symposium on LNG

Storage and Handling, Boumerdes, Algeria, April 4-5, 1978.

24. Tobler, R. L. and Reed, R. P., "Fracture mechanics parameters for a 5083-0 aluminum alloy at low temperatures," J. Eng. Mater. Technol. 19 , 306 (1977).

25. McHenry, H. I. and Reed, R. P., "Fracture behavior of the heat affected

zone in 5% Ni steel weldraents," J. Weld. Res. Supp. (Apr 1977).

26. McHenry, H. I., "Fracture mechanics and its applications to cryogenics,"

in Advances in Cryogenic Engineering, Volume 22 (Plenum, New York,

1977) , p. 9-26.

27. Parrish, W. R., Arvidson, J. M. and LaBrecque, J. F. , "System is

accurate, precise for LNG sampling," Hydrocarbon Processing 5_7, 114

(1978).

28. Parrish, W. R. , Arvidson, J. M. and LaBrecque, J. F. , "Evaluation of

LNG sampling-measurement systems for custody transfer," Proceedings of

American Gas Association Transmission Conference, Montreal, Quebec,.

Canada, May 8-10, 1978.

29. Parrish, W. R. , Arvidson, J. M. and LaBrecque, J. F. , "Development and

evaluation of an LNG sampling system," Nat. Bur. Stand. (U.S.),

Interagency Report 78-887 (in press, 1978).

30. Parrish, W. R. , Brennan, J. A. and Siegwarth, J. D., "LNG custody

transfer research at the National Bureau of Standards," Proceedings of

the American Gas Association Transmission Conference, Montreal, Quebec,

Canada, May 8-10, 1978.

31. Giarratano, P. J. and Collier, R. S., "Evaluation of capacitance

densitometry for LNG mixtures with low nitrogen composition," Ind. Chem.

Eng. Process. Des. Dev. 1_6, 330 (1977).

33
32. Siegwarth, J. D., Younglove, B. A. and LaBrecque, J. F., "An evaluation

of commercial densimeters for use in LNG," Nat. Bur. Stand. (U.S.),

Technical Note 697 (Oct 1977).

33. Siegwarth, J. D., Younglove, B. A. and LaBrecque, J. F., "Cryogenic

fluids density reference system: provisional accuracy statement," Nat.

Bur. Stand. (U.S.), Technical Note 698 (Nov 1977).

34. Siegwarth, J. D., LaBrecque, J. F. and Younglove, B. A., "Test of

densimeters for use in the custody transfer of LNG," Proceedings,

International School for Hydrocarbon Measurement, Norman, Oklahoma,

April 11-14, 1978.

35. Brennan, J. A., "Better LNG flow measurement sought," Oil and Gas

Journal 7_6, 168 (1978) .

36. Collier, R. S., Haber, S., Jackson, R. H. F., LaBrecque, J. F. and

Tryon, P. V., "Custody transfer systems for LNG ships; tank survey

techniques and sounding tables," Nat. Bur. Stand. (U.S.), Interagency

Report (in preparation?

34
The speed of sound in saturated and compressed fluid ethane has been measured in the temperature range 9 7 to 323. 15 K and at pressures to 35 MPa. These data were combined

with newly available PpT data to obtain the isentropic compressibility and the ratio of the R-1030

specific heats. The quality of the PpT data has been examined by comparison of sound

speeds calculated from these data with the measured sound speeds.

Speed of sound in saturated and compressed

fluid ethane

R. Tsumura and G.C. Straty

The data presented here were obtained as part of a pro- gramme to provide accurate thermodynamic properties data

for saturated and compressed fluid ethane to support the development of LNG technology at NBS and throughout

the fuel gas industry. Measurements of the sound speed in saturated liquid ethane

have been made from near its triple point temperature to 303 K at frequencies of 1 and 10 MHz. Comparison of the 10 MHz data with those measured at 1 MHz along the satu- ration boundary indicated no detectable dispersion at higlier temperatures. However, as the triple point is approached, an

increasing difference in sound speeds measured at 1 MHz

and 10 MHz was observed. An interpretation of this apparent

dispersion is discussed. Near the critical point, where the attenuation is high, two different techniques were used to measure the sound speed in the saturated liquid. Comparison

with other data is made through a new empirical equation

which was fitted to tl-ie saturated liquid data. This equation

has only six parameters and is capable of representing the

present experimental data in the entire saturated liquid region v.-ithin the experimental error. In the compressed

fluid, the measurements were carried out along selected isotherms at temperatures from 100 to 323.1 5 K at pressures

to about 35 MPa. The well-known equations

which relate the sound speed WXo the density p, the isen- tropic compressibility K^, and the ratio of specific heats y, have been used together with previously measured pressure,

density, and temperature (PpT) data'"^ to determine and 7 from the measured sound speed for both saturated and compressed fluid ethane.

Experimental apparatus and procedure

The apparatus was identical to that used previously in this laboratory for measurements on hydrogen,* oxygen,'

The authors are with the Institute for Basic Standards, Cryogenics

Division, National Bureau of Standards, Boulder, Colorado 80302, USA. RT is also with the Consejo National de Ciencia y Technologia (CONACYT), Mexico City, Received 7 January 1977.

fluorine,* and methane'' and has been described in detail. Only a brief summary will be given here. Two plane parallel x-cut quartz crystals are pressed to the ends of a tubular invar spacer of accurately known length. An electrical pulse to one crystal generates an acoustic pulse

wliich propagates through the fluid. An output signal is obtained from the second crystal and is observed on an

oscilloscope. The received signal is generated by the pressure wave in the sample striking the receiving crystal. This pres- sure wave has travelled the length of the spacer tube in the

liq\iid .sample. Successive acoustic signals result from echoes which have made multiple transits through this distance. In

the pulse-echo technique used mostly here, the pulse repetition rate is adjusted so the arrival time of a pulse echo at the receiving crystal coincides with that of the succeeding

directly received pulse. Under these conditions, the sound

speed IV is determined by

W = 2df (2)

where / is the pulse repetition frequency and d is the length of the tubular spacer. The uncertainty in the sound speed measured in this way is estimated to be less than 0.05,

increasing somewhat in the region of high attenuation.

The use of the pulse-echo technique near the critical point

is limited because of the large sound attenuation which makes it impossible to detect the pulse echoes. The sound

speed can still be measured by a somewhat different tech- nique, however. Even in the absence of echoes the observed

signals include the directly received acoustic pulse as well as an electric pulse resulting from electronic cross-talk between

input and output circuitry. This electric pulse is received at essentially zero time delay. The position of the acoustic

pulse on the oscUloscope depends on its transit time between

the crystals and is not affected by a change of the pulse

repetition frequency. It is possible to superimpose the electric pulse and the preceding acoustic pulse if the pulse

repetition frequency is.double the frequency used in pulse- echo technique. The sound speed is then given by

W = fd (3)

Since the shape of the electric pulse is different from that of

the acoustic pulse, the proper superposition of the electric and acoustic pulse is difficult to recognize. Therefore this A-1

CRYOGENICS Vol 17, >Io. 4 (Apr 1977) 195
method of determining the sound speed is, in effect, calibrated against previously determined pulse-echo results. At some convenient temperature near critical, where pulse- echo results have been obtained, the pulse repetition fre- quency is adjusted to double that obtained previously. The

relative position of an easily recognized peak on both the

electric and acoustic pulse is then observed. In subsequent measurements closer to the critical point, using the pulseelectric pulse method, the proper pulse repetition frequency

is taken as that frequency which results in the same relative peak positions as observed in the calibration. The pulse-electric pulse technique was used only at 10 MHz

near the critical point. The main source of error in this method is due to errors in adjusting the relative position of the pulses as observed on the oscilloscope screen, but the inaccuracies are estimated to be generally less ttian 0.06%,

increasing to 0.1% very close to the critical point where the krge sound attenuation made it difficult to distinguish the acoustic pulse from the noise.

Pressures were measured by reference through differential pressure transducers to oil pressures derived from an oil dead-weight gauge believed accurate to within 0.01%. Temperatures were measured with a platinum resistance thermometer calibrated by the National Bureau of Standards on the IPTS-68. The maximum uncertainty in the measured

temperature is estimated to be less than 0.05 K. The ethane used was commercially available research grade with

specified minimum purity of 99.98%. This purity was

verified by chromatographic analysis.

Results and discussion The sound speeds in the saturated liquid were fitted to an

equation of the form,

n W(T) = (T^-TT 2 "i^' ('^^

/=o

where 0<a<l, X = \n(T^-T+ \),T^ = critical temperature = 305.33 K. The exponent a was first chosen by trial and error and the coefficients a,- were then found by an unweighted least squares method. The coefficients obtained are as follows:'

flo = 238.6983990 Ji = - 95.64244603 = 39.94268780 fla = - 7.318579991

04 = 0.7402281555 a = 0.32

Increasing the number of parameters showed no significant improvement in the fit. Measured and calculated values are tabulated together with the percent differences in Table 1. From a comparison between values measured at 10 and

1 MHz above 295 K and from the agreement between the data measured with the different techniques mentioned

before no dispersion is indicated.

Equation 4 was used to compare other available data witlv. the present data. Relative percent deviations for saturated

liquid are shown in Fig. 1. Poole and Aziz' and Vangeel'°

estimated an uncertainty of ± 0.2% for their data. However,

16 -

-12 - r, T,

I I J U 1 UL

100 150 200 250 300

Temperature, K

Fig. 1 Deviation plot of sound speeds in saturated liquid ethane compared with values calculated from (4) T •-this vuork at 10 and 1 MHz respectively, o—Vangeel,' A—Poole and Aziz,' calculated' from volumetric and

calorimetric data

their measurements are systematically lower than this work

by about 0.6 and 0.4% respectively near the triple point temperature (90.348 K)." The fact that Vangeel used the same pulse-echo technique but at a frequency of 2 MHz,

suggests that the difference near the triple point could be a dispersion effect. To test this possibility some data were

taken at 1 MHz near the triple point and, as is shown in Fig. 1, were, in general, lower than those of Vangeel reaching

a difference of 0.9% at 91 K. The apparent dispersion was in the same direction to that encountered by Gammon and

Douslin for methane.'^ Although they only took measure- ments down to 1 13 K they found it necessary to make a correction to zero frequency of less than 0.025% for their measuring frequency of 1.5 MHz.

To learn more about this apparent dispersion, sound speed measurements were also performed on saturated liquid methane at 1 MHz. The data obtained were smaller than

those measured by Straty"* at 10 MHz but only by about 0.1% at 91 K. At this temperature the acoustic wavelength

in methane is similar to that in ethane at about 160 K where

the dispersion was also around 0.1%. This simUarity suggested

the possibility that the apparent dispersion could be inde- pendent of the substance depending only on experimental geometry. To verify this interpretation, measurements of sound speed in water were carried out at both 10 and I MHz

with the same sample holder. The measurements were made

near room temperature where the acoustic wavelengths are again similar to those in methane near the triple point. The

results showed that the 1 MHz data were again lower by

roughly 0.1% than those at 10 MHz. These results seem to • indicate that this dispersion is identical to that observed by

Lastovka and Carome''' who made an experimental study of

the speed of ultrasonic pulses in cylindrical, water-filled, metallic wave guides. They used both the pulse-echo tech- nique and a direct source-to-receiver signal travel time method to test wave guides with inside diameters of 1.27, 2.54, and 3.49 cm. At 5 MHz they found that the measured sound speed in water in the temperature range 23 to 30 C

was the same with any of these wave guides and to the free

field value (without wave guide). However for frequencies lower than 5 MHz, the sound speed decreased with both the frequency (4, 3, 2, and 1 MHz) and with the diameter of the

196 A

CRYOGENICS . APRIL 1977
Tabie 1. Speeds of sound H' and derived values of the isentropic compressibility and ratio 7 of heat capacities In saturated

liquid ethane Columns 3 and 4 give the values of ^V calculated from (4) and the percent deviation respectively, e and 1 indicates data measured with pulse-electric pulse technique and at 1 MHz respectively.

/ , K r/e,p„ m s" i^/caic. rn s"' AW, % p, mol 1* /Cg, bra 7

b 1 .U i002.9 — 0.013 21 .656 0.3829 1 .425

95.0 1974.1 1 974.4 — 0.016 21.511 0.3967 1.438 100.0 1 938.7 1938.8 — 0.003 21 .328 0.4149 1 .455 luo.U 1 902.8 1 903.0 — 0.01

21.146 0.4344 1 .473

1 1 U.U 1 00 /.4 lob /.I n n 1 c U.U 1 b on nco 2U.ybo U.4o4y 1 A QO

lien 1 831 .2 1831.1 0.004 20.779 0.4773 1.510

1 in r\

1 .^U.U 1 795.0 1 795.0 0.000 OA [inc zU.byb A CAI 0 U.bUl 2

1 COD l.b2o

1 2o.U 1 759.0 1 758.8 0.014 20.410 0.5266 1 .546

1 30.0 1 722.8 1 722.4 0.024 20.224 0.5540 1.563

1 35.0 1685.9 1685.9 0.002 20.037 0.5839 1 .580 140.0 1649.4 1649.2 0.01

19.849 0.6158 1 .596 145.0 1 61 2.7 1612.4 0.01

19.660 0.6504 1.612 150.0 1 575.5 1575.5 0.001 1 9.469 A COOO 0.6882 1 .627 lOD.U 1 538.3 1 538.4 n nnc 1 9.276 0.7290 1 c 0 1 .b42

1 bU.U 1 501 .

1 501 .1 — n nno U.UU2 1 Q AQO A 770/1 U./ /o4 1 c cc \ .bob

1 03.

1 400.0 I'ibj./ — n nnc U.UUb 1 o.oqID A Qoon 1 c7n

1 /U.U i oc n 1 >1 OC 1 |4ZD. 1 — n nnc U.UUb 1 O.DO/ n Q7CO U.o/b2 1 .bo4

1 /O.U 1388.1 1 388.2 — 0.013 1 0 >1 OC 1 O.40O n no ^c 1 .fay /

1 on n 1 oU.U 1 350.3 1 350.3 n nnn U.UUU 10 000 1 o.2o2 Au.yynm7/ /1 7 1 A 1 . / 1 U

1 oo.U 131 2.1 1 31 2.

n nnn 1 0 n"7

1 o.U/b 1 ACQ i.uby 1 700 1 . / 2.3

1 on n 1 yu.U 1 T7 '5 e 1 z/J.b 1 Z/o. / — n nnc U.UUb 1 / .000 1 , 1 4o 1 . /oO

1 yo.u 100c n IzJD.U — nU.UUZ nm 1 /.bo 1 1

1 .2oocJo 1 7/1 Q 1 . / 4Q

^uu.u 1 1 bb.U 1 1 96.1 — n n 1 1 U.U 1 1

1 7 0 0 1 004 1 .004 1

1 . 7d/bl one n ^Uo.U 1 1 56.9 1 1 57.0 — nO.UU/ nm 1 /.21

1 AAA \ .444 1 7 7>1

1 . / /4

0 1 n n ^ 1 U.U 111 7.4 111 /.o — n n 1 0

U.Ul 2

1 c no A 1 ceo l.bbo 1 70Q 1 . /OO

zl O.U 1 077.7 1077.8 — 0.009 1 c 7 c 11 fa. /bl 1 7 AA i./uy 1 ono

^izU.U 1 037.7 1037.7 — 0.003 1 6.51

1 071 1 .0/1 1 Q 1 7 l.ol / 2Z3.U nm 0 9a/.

997.3 — 0.01

1 C oc

1 fa. 2b / 0 ACC 2.Ubb 1 00>!1 .oo4 nn n zoU.U 956.5 956.5 0.001 1 c n 1 c

1 b.U 1 b

0 07A 2.2 /U 1 .ob2

91 0.2 91 0.3 — n nnc 0.006 1 C 7 CO 1 b. /bJ 0 con 2.b2U 1 Q70

0/1 n n 873.6 o/j.b A An*? 0.00/ 1 c /1 00 1 b.4so 0 Q 1 C 1 QOA 1 .034

o/i c n Z'lb.U 831 .3 831.3 0.001 1 5.201 3.166 1 no A 1 .y2u ocn n ZbO.O 788.5 788.4 0.008 1 4.908 0 coo 1 r\A n 1 .y4y 255.0 745.0 744.9 0.014 14.600 4.104 1 .984 260.0 700.7 700.6 0.021 14.275 4.746 2.026 oc c n ZDO.O 655.4 655.3 0.020 13.930 5.557 2.078 270.0 608.9 608.9 0.008 13.562 6.613

' 2.143 275.0 561.0 561.0 — 0.005 13.164 8.027 2.226

280.0 51 1.4 51 1.4 — 0.006 1 2.728 9.990 2.342 285.0 e 459.4 459.5 — 0.015 1 2.240 12.87 2.507 290.0 e 404.1 404.2 — 0.027 1 1.680 17.43 2.772 295.0 e 343.9 343.9 — 0.008 1 1.003 25.56 3.269

295.0 1 343.9 343.9 — 0.008 1 1.003 25.56 3.269 296.0 e 331.1 331.0 0.030 10.846 27.98 3.429

296.0 1 330.9 331.0 -0.031 10.846 27.99 3.427 297.0 e 317.7 317.7 0.003 10.679 30.85 3.624

297.0 1 317.6 317.7 - 0.029 10.679 30.86 3.622

298.0 e 303.9 303.9 -0.011 10.500 34.29 3.857 298.0 1 303.9 303.9 -0.011 10.500 34.30 3.866 299.0 e 289.6 289.6 -0.017 10.306 38.47 4.183

299.0 1 289.7 289.6 0.018 10.306 38.44 4.186

300.0 1 274.8 274.7 0.031 10.093 43.64 4.618

301.0 1 259.1 259.0 0.057 9.854 50.28 5.240 302.0 1 241.9 242.0 -0.054 9.579 59.32 6.203 303.0 1 223.2 223.2 0.009 9.249 72.18 7.966

CRYOGENICS . APRIL 1977 A-3

197
Table 2. Speed of sounds W and derived values of the isentropic compressibility K', and ratio 7 of heat capacities in compressed fluid ethane

e and I indicates data measured with pulse-electric techniques and at 1 MHz respectively

P, MPa W, m s'' p, mol 1 ' K'j.GPa"' 7 P. MPa W, m s"' p, mol r' K^. GPa"' 7

T = 100.00 K 25.381 1402.5 18.262 0.9258 1.605 21.834 1377.9 18.164 0.9643 1.622 31.949 2051.3 21.709 0.3641 1.398 18.326 1352.4 18.061 1.007 1 .640 28.495 2040.0 21.670 0.3688 1.403 14.831 1325.7 17.955 1.054 1.660 25.195 2028.8 21.633 0.3735 1.408 14.190 1321.0 17.934 1.063 1.665 21.728 2017.3 21.593 0.3785 1.414 11.523 1299.1 17.848 1.104 1.680 18.427 2005.7 21.555 0.3835 1.419 7.881 1268.2 17.724 1.167 1.703

14.981 1993.6 21.514 0.3889 1.425 4.934 1241.6 17.617 1.225 1.724 11.414 1981.0 21.471 0.3947 1.432 7.962 1968.4 21.429 0.4005 1.439 4.122 1954.2 21.381 0.4073 1.447 r= 220.00 K

35.977 1361.0 17.881 1.004 1.574 T = 120.00 K

28.535 1308.1 17.660 1.101 1.609 21.679 1254.4 17.434 1.212 1.647 36.342 1 943,2 21.106 0.4173 1.432 1 D.O 1 0 1 zUU.o 1 Oil n

1.685 28.584 1914.2 21 .006 0.4321 1 .449 1 y1 "7 QO 1 1 C\A 0 17 1 7Q 1 /. 1 /y 1.3 DO 1.691 18.912 1876.1 20.875 0.4526 1.473 lU.Uo/ 1 1 't /.o 1 6.983 1.486 1.725 14.963 1 860.0 20.81

0.461

1 .483 1 n noQ 1 U.U/d 1 1 4 /.D 1 c noo 1 .487 1.725 8.105 1831.0 20.71

0.4787 1.503 7.875 1 125.4 16.886 1.555 1.745

T = 140.00 K r = 240.00 K

35.565 1819.4 20.451 0.4913 1.477 34.279 1242.2 17.163 1.255 1.591 28.434 1788.1 20.343 0.5113 1.496 28.538 1 195.8 16.957 1.372 1.622 21.457 175G.7 20.231 0.5327 1.517 21.670 1 134.4 16.581 1.549 1.666 14.708 1725.2 20.118 0.5554 1.540 14733 1063.4 16.357 1.798 1.721 7.800 1690.7 19.995 0.5818 1.565

/.oD / Qpn you. 1

1 1 Q7A 0 1 Z. 1 00 1 7QO

Q11 7 T / .0 1 D.Do^ 1 OC

T = 160.00 K

35.328 1698.2 19.805 0.5823 1.513 / = 260.00 K

28.145 1662.8 19.676 0.6113 1.537 34.541 21.806 1529.9 19.556 0.6402 1.560 1 142 5 IK /1Q1 1 roe;

1 .t}yo 14.846 1591.7 19.416 0.6761 1.587 J 1 .yo/ 1 1 on 1

1 6.384 1.618 1.609 8.013 1551.5 19.268 0.7170 1.617 OD /I ~IQ 1 nQ7 Q 16.229 1.732 1.632 25.289 1056.6 16.078 1.853 1.655 22.529 1028.1 15.937 1.974 1.678 21.770 1019.5 15.896 2.013 1.683

T-= 180.00 K 17.581 971.2 15.657 2.252 1.723 14.835 936.3 15.482 2.450 1.754 35.697 1 tiRT A. 1

1 Qy.

1

1 7n/ u u.oy 1 y 1 .OH \ 11.364 887.6 15.235 2.771 1.801 28 61

1 RaT R 1 Q n? 1 U. / ooO 1 7.801 830.2 14.942 3.229 1.852

91^ 1 .ouu Rnn 11 "^09 ou^.un 1 o.ooz u. / 0 1

1 txQf;

1 .pyo 5.134 780.0 14.684 3.723 1.921 14.716 1457.9 18.693 0.8371 1.628 11.517 1435.6 18.610 0.8671 1.643 7.879 1410.3 18.511 0.9033 1.664 T= 280.00 K

36.829 1068.5 15.902 1.832 1.584 T = 200.00 K 34.921 1050.9 15.812 1.905 1.595 32.035 1023.2 15.669 2.027 1.614 36.754 1475.4 18.551 0.8236 1.557 28.585 987.7 15.484 2.201 1.640 32.140 1446.9 18.438 0.8615 1.575 28.535 987.4 15.481 2.204 1.641 28.520 1423.6 18.346 0.8945 1.591 25.321 952.0 15.293 2.400 1.668

198 A

CRYOGENICS . APRIL 1977
Table 2. Continued

P,MPa W.ms'^ p, mol I"' /C^, GPa"' 7 MPa M/, m s"' p, mol 1"' /C,, GPa''

21.684 908.2 15.058

21.654 907.7 15.056

18.345 863.9 14.814

14.752 809.9 14.512

14.738 809.9 14.510

11.310 750.2 14.166

7.824 676.0 13.728

7.804 675.7 13.725

4.998 598.0 13.253

r= 280.00 K

36.829 1068.5 15.902

34.921 1050.9 15.812 32.035 1023.2 15.669 28.585 987.7 15.484 28.535 987.4 15.481 25.321 952.0 15.293 21.684 908.2 1 5.058 21.654 907.7 15.056 18.345 863.9 14.814

14.752 809.9 14.512

14.738 809.9 14.510

11.310 750.2 14.166

7.824 676.0 13.728

7.804 675.7 13.725 4.998 598.0 13.253

r= 300.00 K

35.788 971.1 15.152 30.764 918.0 14.852 28.535 892.6 14.704 28.502 892.0 14.702 25.137 850.7 14.457

21.711 804.1 14.174 21.672 803.6 14.170

18.200 750.2 13.836

14.341 690.4 13.444

13.268 1 658.2 13.228

11.337 1 614.0 12.919

11.304 613.3 12.914

9.547 566.2 12.571 8.753 541.8 12.389 7.928 1 513.6 12.172

7.823 509.8 12.142

7.821 509.8 12.142

7.815 509.6 12.140 7.036

e 478.7 11.895 7.000 477.2 11.883

6.177 e 438.3 11.561 5.735 1 413.2 11.347

5.565 e 402.6 11.254

4.855 e 346.2 10.746 4.610 e 318.4 10.488

4.584 e 314.9 10.456

£..0/0 1 7ni^ ^.00 1

1 746 24.830 821.5 3.494 1.801 21.127 768.9

3.494 1.802 18.210 722.0

4.171 1.874 14.694 656.1 5.302 1.983 11.461 1 581.3

5.308 1.985 11.324 577.8

7.017 2.132 10.156 1 544.8

8.269 1 480.6

7.711 e 457.8

7.427 1 445.1 6.085 1 369.2

5.701 e 338.7

1.832 1.584 5.260 1 289.9

1 ^Qt^ 5.222 1 284.4

1 .0 1 H 5.088 1 261.7

2.201 1.640 5.052 I 254.2

2.204 1.641 5.023 1 247.5

2.400 1.668 4.996 1 240.6 2.678 1.705 4.930 1 218.2

2.681 1.704 3.008 1.746 3.494 1.801 3.494 1.802

4.171 1.874 5.302 1.983

877.1 5.308 1.985 34.482

7.017 2.132

0 1 . 0 1 u

97 /IQR 7Q9 R

91 R4Q 707 R

1

1 Ru.oo/ Kino

1 0.00 1 R1 fl Q

Id 707 R7? J / 0.0R

11 1

1 .zoo 9RR d7Q 7 2.327 1.586 2.657 1.624 2.839 1.644 7 Rn9 0 '59R 1 2.843 1.644 9Q7 9 3.179 1.679 3.629 1.722 3.634 1.723 4.271 1.781 5.190 1.858 T - 5.803 1.907 6.829 1.985 33.170 850.1 6.846 1.988 28.536 793.5

8.252 2.092 25.1 14 746.6

9.143 2.156 21.665 693.5

10.36 2.241 17.178 1 61 1.3 10.54 2.254 14.694 556.5

10.54 2.255 13.346 1 521.9

10.55 2.256 10.176 1 419.9

12.20 2.370 10.034 e 414.6

12.29 2.377 9.077 e 372.8

14.98 2.562 9.061 1 371.7

17.16 2.713 8.035 1 316.2

18.23 2.788 7.049 1 250.7

25.82 3.326 6.707 1 231.8

31.28 3.724 6.323 1 223.5

32.08 3.783 6.063 1 224.5

r= 305.33 K

14.205 3.469 1.684 13.872 4.055 1.736 13.565 4.704 1.790 13.113 5.891 1.882 12.567 7.830 2.021 12.540 7.945 2.029 12.285 9.122 2.109

11.759 12.24 2.318 11.559 13.73 2.419^

11.446 14.67 2.481 10.716 22.76 3.044

10.387 27.91 3.442

9.810 40.35 4.535

9.738 4Z22 4.730

9.429 51.48 5.799

9.321 55.21 6.292

9.219 58.91 6.834

9.113 63.04 7.500

8.741 79.94 11.008

r= 320.00 K

14.351 3.012 1.590 14.145 3.300 1.613

13.811 3.831 1.656 13.225 5.024 1.741 12.500 7.129 1.874 12.499 7.130 1.874 12.196 8.282 1.943 11.346 12.76 2.197

10.875 16.27 2.392

10.145 23.62 2.811 9.495 32.53 3.342

8.937 4Z13 3.911

323.15 K

14.141 3.254 1.598 13.772 3.835 1.643 13.452 4.435 1.686 13.073 5.289 1.742 12.444 7.152 1.853 11.983 8.961 1.958 11.675 10.46 2.038

10.628 17.74 2.422

10.561 18.31 2.458

10.029 23.86 2.754

10.018 24.03 2.755

9.138 35.39 3.403

7.495 70.61 4.424

6.618 93.54 4.453

5.522 120.5 4.245

4.832 136.6 3.689

CRYOGENICS . APRIL 1977 A-5

199
Pressure , MPa

Fig. 2 Speed of sound in saturated liquid « and in compressed

liquid o ethane as a function of pressure

wave guide and they concluded that this kind of effect could be explained on the assumption that a pure plane wave

is not propagated. The inside diameter of our spacer was

about 1 .9 cm, and from the former discussion it is behaved

that the data measured at 10 MHz is free from this kind of

dispersion but that it probably affected this work at 1 MHz

near the triple point and also the work of Vangeel at 2 MHz.

It is not possible to conclude whether the measurements of Poole and Aziz were affected in the same way because they used a resonance technique.

Sound speeds for saturated liquid ethane, calculated' from

volumetric^ and calorimetric data,''* are compared with

the present sound speed measurements in Fig. 1 . Although

in the critical region the difference becomes large, at temperatures below 270 K the maximum difference is approximately 1 .6%. The overall agreement between measured and calculated values is not unreasonable in view

of the great demands placed on the precision and accuracy of

the PpT data and its representation and of the rather complicated series of calulations necessary to obtain sound

speeds from PpT and specific heat data. The measured sound speeds for the compressed fluid are tabulated along isotherms in Table 2 and plotted as a function of pressure in Fig. 2. No measurements for the sound

speeds in the compressed liquid are available for comparison. Measurements by Terres et al" along a compressed gas isotherm at 323.15 K are lower than this work by about

2 to 4% in the pressure range 8 to 10 MFa but higher at pressures around 6 MPa. We can offer no explanation for

this difference.

Sound speeds calculated' for compressed fluid ethane from

volumetric data^ and calorimetric data'* were compared

with the present sound speed measurements (see reference 1

,

Table 19). The agreement in the compressed liquid (at 300 K

and below) is in general within 1% except neat the triple point where the differences increase to 2%. The quality of

the PpT coi relation of Goodwin et al is manifested again

by the general agreement within 1% with the data for the

single phase fluid.

The measured sound speeds have been combined with newly

available volumetric data^ to calculate adiabatic compressibilities A's = — (1/K) (3F/3/')5 and specific heat ratios 7 = Cp/Cy. The results are given in Tables 1 and 2 for the saturated and compressed fluids, respectively. Far from the

critical point, the uncertainty is is estimated at about

+ 0.3% due to the combined uncertainty in the measured sound speed and the maximum uncertainty in the density estimated by Goodwin' at ± 0.2%. The uncertainty in 7 is expected to be somewhat larger because of the larger uncertainty in the derivative {t}P/dp)x obtained from the PpT

data. It is difficult to estimate the uncertainty in 7 but examination of the differences between the measured and

calculated speed of sound suggest the uncertainty is less than 2% at higher temperatures and lower densities far from the

critical point. For the low temperature high density liquid region where (dP/dp)x becomes very large and where

accurate determination of this derivative becomes very

difficult the uncertainty is estimated to be less than 4%.

Near the critical point the uncertainty in 7 and K^, is estimated to be several percent, as is suggested from the differences between the measured and calculated speeds of

sound, and is the result of the inherent difficulties associated with measurements near critical points.

We would hke to thank D.E. Diller for his useful comments

and helpful discussions during the course of this research.

References

1 Goodwin, R.D., Roder, H.M., Straty, G.C. NBS (US) Tech

Note 684, forthcoming

2 Straty, G.C, Tsumura, R.J Res NBS (VS) 80A (1976) 35

3 H.-iyncs, \V.N(., Hiza, M J. / Chem Thermo (forthcoming) 4 Younglove, R.A. y/lcoKir 5oc.4m 38 (1965) 433

5 Stiaty, G.C, Younglove, B.A. / Chem Viermo 5 (1973) 305

6 Stiaty, G.C, Younglove, B.A./Oiem Pbys 58 (1973) 2191

7 Stnty, G.C Cryogenics 14 (1974) 367

8 The number of digits in these coefficients are given in order to reproduce the table and are not all necessarily significant 9 Poole, G.R., A7iz, R.A. Can J Pliys 50 (1972) 721

10 Vangeel, E. Katholielce Universiteit, Leuven, Belgium, unpublished data

11 Straty, G.C, Tsumura, K.J Chem Phys 64 (1976) 859

12 Gammon, B.E.,Douslin,D.R.ycy;c/n Phys 6* (1976) 203

13 Ustovka, J.B.,Caroine, M.V.J Acoust Soc Am 35 (1963) 1279

14 Roder, U.M.J Res NBS (USJ 80A (1976) 739

15 leries, V.E., Jaltn, \V., Reissmann, M. Brcimstoff-Chemie 38

(1957) 129

200 A-6 CRYOGENICS . APRIL J977
A Correlation of the Existing Viscosity and Thermal

Conductivity Data of Gaseous and Liquid Ethane

H. J. M. Hanley

Cryogenics Division, Institute for Basic Standards, National Bureau of Standartis, Boulder, Colorado 80302

and

K. E. Gubbins and S. Murad

School of Chemical Engineering, Olin Hall, Cornell University, Ithaca, New York 14353

Data for the viscosity and thermal conductivity coefficients of ethane have been evaluated and

represented by an empirical function. Tables of values have been prepared for the range 200-500 K,

for pressure to 75 MPa (= 750 aim). The tables include an estimate of the anomalous contribution

to the thermal conductivity in the neighborhood of the critical point. The estimated uncertainties of the tabular values are ±5% and ±8% for the viscosity and thermal conductivity coefficient, respectively.

Key words: Critical point enhancement; data evaluation; ethane; thermal conductivity coefficient; viscosity coefficient.

Contents

Page Nomenclature 1167 Table 6.

1. Introduction 1168

2. Correlating Equations 1168

2.1. The Equation of State 1169

3. Data 1169

3.1. The Dilute Gas 1169 Figure 1.

3.2. The Dense Gas and Liquid 1171

3.3. The Critical Region 1171 Figure 2.

4. Tables of Values 1174

4.1. Uncertainty of the Tables 1171 Figure 3.

5. Conclusion 11 71

6. Acknowledgments 1179 References 1179 Figure 4.

List of Tables Table 1. Dilute gas parameters for equations (7) Figure 5. and (9) 1171 Table 2. m-6-8 potential function parameters Figure 6. and critical point parameters for ethane 1171 Figure 7. Table 3. Parameters for equations (3-5) 1172 Table 4. Viscosity coefficient of ethane for Figure 8. various temperatures (K) and pressures (MPa) 117;5 Table 5. Thermal conductivity of ethane for vari- Figure 9. ous temperatures (K) and pressures (MPa) 1177

Viscosity and thermal conductivity

coefficients of saturated liquid ethane... 1179

List of Figures

Plot of the excess viscosity coefficient versus density 1169

Plot of the excess thermal conductivity

coefficient versus density 1170

Deviation plot between dilute gas vis- cosity data and values calculated from

equation (7) 1170

Deviation plot between dilute gas ther- mal conductivity data and values calculated from equation (9) 1171

Deviation plot for the viscosity coeffi- cient at the saturated liquid boundary... 1 172

Deviation plots for tlie viscosity coeffi- cient for several isotherms 1172

Deviation plots for the thermal conductivity coefficient at 315 K 1173

Deviation plots for the thermal conductivity coefficient at 649 K and

406 K 1173

Plot of the calculated excess thermal

conductivity coefficient, using equation

(10), at 305.7 K, 310 K, and 400 K 1174

T

PKt

Nomenclature

temperature

pressure

compressibility

Copyrighl © 1^77 by ihe U.S. Sfcreury of Comrurrrc on behalf of the United Stain. Thii

copyn^ihl will be aatigned lo the American Inslitule of Phyeics and ihr American Chemjca

Society, lo whom all requests regaxding reprodurtion should be addressed.

p mass density

viscosity coefficient

dilute gas viscosity

viscosity first density correlation

At; excess viscosity

Atj' dense gas and liquid viscosity

critical region excess viscosity

h (t=l,7),£ viscosity equation parameters

1167 B-1

J. Phy». Ch«m. Ref. Dota, Vol. 6, No. A, 1977
1168 HANLEY, GUSBINS, AND MURAD

GV(i) (i=l,9) dilute gas viscosity equation parameters X thermal conductivity coefhcient Xo dilute gas thermal conductivity

X, thermal conductivity first density cor- rection AX excess thermal conductivity AX' dense gas and liquid thermal con- ductivity AXc critical region excess thermal conductivity

Ai(t=l,7),D thermal conductivity equation paraineters GT{i) (/=1,9) dilute gas thermal conductivity

efjuation parameters

M molecular weight

N Avogadro constant k . Boltzmanu constant

ti& intermolecular pair potential m, y' , a\ r,„, d, e potential parameters

A, B, F first density correction equation

parameters

0 viscosity and thermal conductivity

equation variable

* reduced variable superscript

c critical point variable subscript

Xo, E\, £2, scaling parameters for the comprcs6, y sibility in the critical region

R length parameter in llie critical point

equation

fL chemical potential A' viscosity critical region parameter

(In the last ten years or so, the conventional experi- mental procedures (e.g., the capillary flow and oscillating disc methods for the viscosity, and the hot wire and

parallel plate methods for the thermal conductivity) have been re-examined and new techniques and modifications have been proposed [5].) In summary, we do not think it possible to present

authoritative tables, with a significant assessment of accuracy, until more, and more accurate, data are

available. However there is considerable technical

interest in ethane at this time and it was felt worthwhile

to present tables of both the viscosity and the thermal

conductivity coefficients over a wide experimental range. Guidelines for work which v/ould lead to improved tables are suggested.

In reference [1], criteria for evaluating data in the

literature were discussed, and an equation for the vis- cosity and thermal conductivity coefficient was proposed. This paper will follow closely the format of reference

[1]. so the criteria and the correlating equations will be

used here v.'ilh only minimal comments.

2. CerrelatSrig Equations

The correlation for ethane is based on the be' ; vior of the transport coefficients with respect to temperature

(T) and density {p) according to the equations

r,{p, T) = 77„(r) + Tji(r)p + A7,'(p, T)^-^l)c{p, T),

(1)

1. Introduction

In reference [1]' we set up a procedure to evaluate and represent the viscosity coelTicient (-17) and the thermal conductivity coefRcient (X) of simple fluids which has been applied to argon (with krypton and

xenon), oxygen and nitrogen [1], and to methane [2, 3]. The object of this work is to include ethane; specifically

to present tables of values of the transport coefl[icients covering a broad range of experimental conditions. Several correlations of the ethane transport coeffi- cients have been published [!]. Most, however, are

restricted to one coefficient and most cover a limited experimental range. One of the difficulties is that the data base cannot be considered satisfactory by comparison with those of other simple fluids, such as the

fluids studied in references [1-3]. For example, there arc some gaps in the data coverage and the majority

of the data available was published more than ten years

ago. Data cannot, of course, be judged solely by their publication date, but it is generally accepted that much

of the older data for many simple fluids are suspect.

x(p, T) = Xo(7') -f x,(r)p + A\'(p,r) + A\,(p,r)

(2)

for the viscosity and thermal conductivity, respectively.

In these equations, t;o(7') and Xo(r) are the dilute gas values; 171 (r) andXiCT) represent first density cor- rections for the moderately dense gas; while A7)'(p, T) and AX'(p, 7") are remainders. The term r]\{T) is given by the empirical expression

n,iT)=A + B [C-!n iTIF)]^ (3)

and similarly for Ki(T). The coefficients A, B, C and

F can be found from a fit of data, but we set F = cjk

where € is the energy parameter of the methane pair

potential function and k is Boltzmann's constant. See

section 3. The terms At)'(p> T) and AX'(p, 7") are expressed

empirically by the relations

Atj' (p, T)=E exp [/i +j.>IT] { exp

[p« ' O2 +hlT''^- ) + ep" 'ij:,+j,IT+jv'Tn] - 1.0},

(4)

' Figures in brat-Lcis in(licAle lileraiure rcft-n md

J. Phyi. Chem. Rof. Oafa, Vol. 6, No. 4, 1977 B-2
TRANSPORT PROPERTIES FOR ETHANE 1169

AX'(p,r)=Z)exp [ki + kJT]{exp

[p'>Hk2 + kJT^i'- ) + dp''Hh+h6lT+ hlT'')]- 1.0}.

(5)

The parameter 0 is included to account specifically for the high density behavior of the transport coefficients and is a function of the density with respect to the

critical density, p^:

6= (p-Pc)/Pc (6)

The coefficients, E, D, ji . . . Jt, k\ . . . kj, are to be

obtained from experimental data. Finally, equations (1) and (2) include the terms

A7jc(p, T) and AA.e(p, T), respectively, to account

for the known enhancement of the coefficients in the

vicinity of the critical point, see section 3.3. As the form of the equations suggest, the transport

coefficients are correlated and evaluated by examinirg

their behavior with respect to density: thus for the

viscosity, (a) we first evaluate the dilute gas and (b), with the critical region excluded, the experimental

quantity (Tj„p(p, T) — T)a{T)) is identified with the terms r\\{T)p + A-q'{p, T). Similarly for the thermal

conductivity. The critical point behavior is treated

separately.

2.1. The' Equation of State

Since the correlation of the transport coefficients requires temperature-density coordinates, but the

majority of data are reported in temperature-pressure

coordinates, an accurate equation of state is essential. The equation of state for ethane used here was derived by Goodwin and discussed in reference [6].

3. Data

Our search of the literature produced the following papers reporting experimental measurements for the transport coefficients of ethane: viscosity, references

[7-21], thermal conductivity, references [10], [13],

[22-30].

Criteria for selecting data for correlation are discussed

in section 2 of reference [1] and the ethane measure- ments were evaluated according to these criteria as

far as possible. For example, it was pointed out that a plot of the excess function Atj or A\ (defined as

T?exp (p, T) —TioiT) and X^xp (p, T) — XoCT), respectively) versus density leads to a good first guess as to the precision and internal consistency of a given data set;

it is a convenient format to compare dilferent data

sets; the plot also allows one to judge if the quahtative behavior of the coefficients for ethane is consistent with

that of other simple fluids. We constructed figures 1 and 2 for the excess functions of ethane. Dilute gas data were represented by the empirical function discussed in section 3.1. Based on

the corresponding behavior of simple fluids other than

1200

1000

800

600

400

200

o

o

o

oo

o

OS

5 10 DENSITY, mot/!

15

Figure I. Plot of the excess viscosity coefficient versus density. O 17), 0 U% A 13]. [20].

ethane (Ar, N2, O2, CO2, F2, H2, CH^, etc.) one would

expect that both A17 and A\ for ethane would be es- sentially temperature independent at a given density.

(See figure 1 of reference [1], however.) The plot for the excess viscosity coefficient for several temperatures,

figure 1, is in fact a reasonably smooth curve, but the

plot for the excess thermal conductivity coefficient shows considerable scatter. The behavior of the excess thermal conductivity coefficient suggests that much of this data is of questionable quality. In summary, the data base for this correlation is refer- ences [7-13], [15], [19] and [20] for the viscosity, and

references [13], [22-27], and [30] for the thermal conductivity. Equal weight was given to the measurements

reported in these sources.

3.1. The Dilute Gas

It is convenient to consider the dilute gas," the dense

gas and hquid, and the critical region separately, as suggested by equations (1) and (2).

Viscosity Coefficient Data from references [7-15] were fitted to the

empirical function found suitable in our previous work

[1,2]:

B-3

J. Phyt. Cham. Ref. Data, Vol. 6, No. 4, 1977
1170 HANLEY, GUBBINS, AND MURAD

120

100

80

-T 60

40

20

o

o

oo

o

oo o

o

8^' u 5 10 15 DENSITY. mol/£

Ficure2. Plot of the excess thermal conductivity coefficient versus density. V

(25-271. 0[22|, A 123). 0 130], , saturated liquid values, see text, section 3.2.

7jo=CF(l)r-' + CF(2)r-2/3 + CF(3)7'-i'3 + CF(4) + CF(5)r>/3 + CF(6)P'3 + c:F(7)r + CF(8)P'3 + c^/(9)75/3. (7)

Values of the coefficients, GV{1) . . . GJ^{9), are listed

in table 1 and a percent deviation plot is shown in figure

3. In this figure, and in subsequent figures, percent

deviation is defined as

^^(expt) — T](calc) T)(expt) X 100. (8)

Of the data fitted, those from reference [15] are judged

to be the most accurate with an estimate of inaccuracy

(uncertainty) of ± 0.5% (see the discussion in reference

[1]). However, only two values at room temperature are reported. An objective assessment of the uncertainty

in the data from the other autliors is difficult since details of the experiments are often not available; some of the data have been extrapolated to lower pressures; the data of reference [11] can be expected to be slightly in error based . on our analysis of the apparatus used [31].

It turns out, however, as can be seen in figure 3, that the data of all authors are within ±2%. Overall, we esti- mate that values of the viscosity coefficient generated from equation (3) are accurate to ±4%.

1.6

0.8 zo

I—<

UJ° 0

t—zLUoEE

UJa-

-0.8

-1.6

1 1 1 I 1 •

-

-

Q O Q o

°

A

n

V H \ cta 1,

c» • *

o

e e °

V o

A O

J> AO o ^ O

1 00| o

1° 1

160 240 320 400

TEMPERATURE, K

480 560

FicliRE 3. Deviation plot between dilute gas viscosity data and values

calculated from equation (7): 0(7), © (8|. V ( 101, [O], 0 [

1 51.

[13]. A (12), A (111

Thermal Conductivity Coefficient

Dilute gas thermal conductivity data from references

[13], [22-27], [30] were fitted to equation (9):

ko=CT{\)T'' + CT{2) -f cr(3 ) + cr(4

)

+ Gr(5)T'i^+GT(6)T'i3 + CT{7)T + GT{8)T'i^+GT(9)T^i\ (9)

which is of the same form as the dilute gas viscosity

equation (7), Values of the coefficients, Cr(l) . . .GT{9)

are listed in table 1. A deviation curve is shown as figure

4. The thermal conductivity data cannot be considered

to be very accurate (cf,, fig:ure 2); there is scatter be- tween data sets and the internal consistency is often poor for a given data set. An estimate of inaccuracy of the values obtained from equation (9) is ± 6%.

Theoretical Calculation of the Dilute Gas Transport

Coefficients

In our previous work [32], it has been shown that

kinetic theory and statistical mechanics can be useful

aids to assess the consistency and accuracy of data. For

several gases, carbon dioxide for example [32], it was

possible to show that the independently measured properties, tlie viscosity and thermal conductivity coeffici- ents, the thermal diffusion factor, and the equilibrium

pressure and dielectric vrrial coefficients, were mutually

consistent. The potential function required to carry

out the calculations was the m-6-8 discussed extensively

J. Phy». Chem, Raf, Dato, Vol, 6, No, 4, 1977 B-4
TRANSPORT PROPERTIES FOR ETHANE. 1171

DILUTE CAS PlRll^ETERS FOR ECU4TI0NS

(71 kHD (91. UNITSI tEMPERlTURE IN

K, VISCOSITY IN l1ICR0-0/(CN»SI AND THERHtL CONOUCIIVITT IN HILLI-M/IH'K)

GV(ll*-.19«7»9ll699E»0a

CV(2)< .lZ6SZ3<i*i25E*0S GV(3l<-.2eaZ<>>661]E*07

CV(i>l' . lS18t9»ZS8E*06

GV(S)« .2k211665aiE*0V GW(6H .5»i*7ZTZ5i.bt»tlt

GVI7tx-.15i.r97<iSl7E+0i.

CVItl' .137921<>ti>9E*03

Gy(9)'-.<*3l]tStiaO<>E*01

CKll S-, ia93;slZ3>E«0 6 GT(2>< , 93S«aZ099SE»07 GT(3I«-.296Z17579JE»0 7

CT(«)s .312Sll)5ib9E>0fc GT(SI' .•S^6aa7i>52E*05

GT«6l«-.173092i>3'.6E»0S

GT(7)> .212a0929i9E*a<> GT(ai:-.1237t26311E»03

CT(9)* .286976a987E«al

150 250 350 450 550

TEMPERATURE, K

650 750

F(GtRe 4. Deviation plot between dilute gas thermal conductivity data and

values calculated from equation (9): 0 [30], V [23], A [24], A [ 1 3], 125,27], 0 [22).

in references [1, 2], [32] and elsewhere^. Following our

previous work therefore, we have obtained m-6-8 para-

* The m-6-B poteaUMi i» given by the expreasioo to 1 I -— , jl6 + 2>'ll<^'')-— ' y'ir -8)] (d/r-j'-T'ld/r-)'

j JJi 6 where d = r»/<r and r* « rla. The dielince ptramrlers a and r„. and the energy parameter,

e. are defined by the reIalion»hip5 <l»(r_ ) = —e and0(cr) =0 whiley' ie a parameter represent- ing inyerae eighth attraction in the potential.

meters for ethane from the viscosity data which are

listed in table 2.

Table 2. m-6-8 potential function [1] parameters and critical point parameters for ethane

Critical point constants

Tc = 305.4 K

Pc = 0.2015 ij^cms (6.70 mol/1) P, = 4.8755 MPa (48.117 atm)

/V/ = 30.07

Parameters for equation (15)

£, = 2.1 Ei = 0.2S7

:(« = 0.166

/3 =0.355

y = 1.190

8 =4.352

m 6-8 parameters

tik = 240.0 K

cr = 4.38 X 10-'» m

r„ = 4.88 X 10-"» in y' = 3.0 m = 11

3.2. The Dense Gas and Liquid

Having values for tjo{J), and with t^rfip, T) set equal

to zero, dense gas and liquid data were fitted by the method of least squares [1] to the terms qi{T)p + Ar)'

(p, T) of equation (1). The data selected were those of references [7], [8], [19] and [20]. Equal weight was given to the data points. The accuracy of the data was judged to be ±5%.

Values of the coefficients A, B, C, F, and J\ . . . Ji

are ^ven in table 3. Similarly for the thermal conductivity coefficient: the data selected '.vas extracted from references [22], [23],

[25-27] and [30]. As noted for figure 2, much of the data must be regarded as suspect. It is difficult to justify anything but to give equal weight to all data points.

One of the drawbacks of the thermal conductivity data base is that no values for the saturated liquid are

available, but we have found by experience that equation

(5) for A\' requires data at, or close to, saturation if the equation is to represent properly the dense liquid. To ensure, therefore, that equation (5) is well-behaved

at low temperatures and high densities, we considered dummy saturated Liquid points obtained from the excess

function graph, figure 2. Sample deviation curves are given in figures 5-8

which indicate that the data have been fitted to within

their estimated accuracy.

3.3. The Critical Region

Thermal Conductivity As remarked, the quantity Akdp, T) of equation (2) represents the anomalous behavior of the thermal

B-5 J. Phyi. Chem. Ref. Data, Vol. 6, No. 4, 1977
1172 HANLEY, GUBBINS, AND MURAD

TABLC3. P»a»M£TERS fOR EQU4TI0NS «3I-(5I.

UNIISl lENPERATURE IN K, VISCOSITY

IN «ICR0-6/(CH»S) »N0 TMERM4L CON- OUCTlylTT IN MLtl-M/ (H«K) .

VISCOSITY EQUATION 3 A>-3.fli393979

a«<>. 202777039 C'l.lZ

r>30s.<i EQUATION « E'1.0

Ji'-.tooseziiieiE^oz J2= .3709'."i7b83E»00

J3' . 17330&31<><>E*02

Jl.« .121<.72l69aE»05

J5«-.3715982l.90E«0'.

je' .193l>9l>&036C«03

J7i . S66959bl'3bE*0Z

THERMAL CONDUCTIVITY EQUATION 3 A'.205S69Z>>90S

B». 9161091735*

F«305.ii

EQUATION S O'l.O

Kl>-.9'i3l<S32l)091E*01

IC2» .19662B79028E»01

K3= .130599369HE»02

K<>i .l><aii;«7Z6«E«06 K5»-.J775503e67SE»05

K6' .1373ei<92230E*0<>

IC7«-.910'.99'.3 3 75E*0 3

0.24 0.32 0.40 0.48 0.56 DENSITY, g/cm'

Figure 5. Deviation plot for the visiosily coefficient at saturated liquid boundary. DaU from reference [19] compared to equation (1).

VISCOSITY O

O

O • O *

° OA O o

VISCOSITY

iP

B

I D

a o

0 08 0 16 0.24 DENSITY, g/cm^

0 32 0 40

Figure 6. Deviation plots for the viscosity coefficient for several isotherms:

top. © [7] at 294 K. A (8| at 326 K; 0 (7J at 327 K; bottom, B[8) at 478 K, a (7J at 511 K.

conductivity coefficient in the neighborhood of the

critical point. There is no doubt that AX^ can contri- bute significantly to the value of the thermal conductivity coefficient and has to be included in a

correlation [1]. Conductivity data, however, in the

critical region for ethane are nonexistent, hence AX,, is obtained by calculation. The procedure is discussed in section 3.2 of reference [1] and in reference [33]. According to reference [33],

exp (-18.66 AP) exp (-4.25 Ap*), (10)

J. Phyi. Cham. Rof. Data, Vol. 6, No. 4, 1977 B-6
TRANSPORT PROPERTIES FOR ETHANE 1173

1 1

- THERMAL CONDUCTIVITY

i i

o

o o

o

0 ' ! 1 -1 1

° -X

O

O C 0°^

OO 0

o 3 1

o

1 ! 0.08 0 16 DENSITY,

0.24 g/cm^

0 32 0,40

FlCLBE Deviation plots for the thermal condurtivity coefficient at 31SK. Dau from reference |26J compared to equation (2).

R = r%- Np

J*

2773

y'(m-8) m — 6

e/A3

the

(12)

v.here T'=T'(€lk). m. y' . r,„ parameters uf table 2. One can see that the calculation of AX^ at a jdven

density and temperature requires the viscosity, the

derivative (dPi'dT)p, and Kt- The viscosity is obtained from our correlation, and {dPldT)p and Kt can be

obtained from the equation of state [6]. Hov,ever, it turns out that wbile the determination of {dPldT)p

presents no real difficulty, the determination of Kt

does; it is now well-known that the classical, analytical,

equations of state cannot describe the large compressibilities in the critical region. The equation of Goodwin

used here, however, is nonanalytic and could, in principle, be used for Kt- Nevertheless, we prefer to be

consistent with our previous work and introduce the scaled equation of state:

p2KT=-^\^p\' h(x) --

A'

:.t) (13)

a a

o

o

THERMAL CONDUCTIVITY

-el \ \ \ \ 0 0.1 0.2 0.3 0.4 0.5 DENSITY, g/cm^

FlctRE 8. Deviation plot for the thermal conduclivitv- coefficient at 649 K, EH

and 406 K.. 0. Data from reference [22].

where

lT=\T-T,\IT,:\p=\p-pAlp.. (11)

with 7c and pc the critical temperature and densitv, respectively. In equation (10), k is Boltzmann"s constant, N is Avogadro's constant, Kt — {ip/ dP)T (the compressibility), R is a length parameter and M is the molecular weight. R is given by:

where h' (x) = dh{x)jdx. The derivation of equation (13)

is based on the observation that the asymptotic behavior

of various thermodynamic properties can be described

in terms of power laws when the critical point is approached along specific paths in the AT— Ap plane. For example, the density along the gas and liquid branch

of the coexistence curve varies asymptotically as |Ap| 0^ lArj^; the chemical potential /x(p. 7") along the

critical isotherm varies as p.(p. T^) — p.{p^,

|Ap|*; the compressibility Kt and specific heat Cp at constant pressure vary along the critical isochore as

I AT I""'. The quantity jc is given by the ratio:

i = Ar/lAp|i'S, - (14)

and h.{x) is a function:

(15)

This equation contains the critical parameters Pc and

Tc (through the definition of x), two critical exponents

/3 and y[ =/3(6— 1)]. and three constants xo, Ei and

£2- Values of the constants and exponents are listed in table 2.

-As an example, the total thermal conductivity coeffi- cient X(p. T) has been calculated at three temperatures: 400 K, 310 K and 305.7 K. The appropriate excess function AX[ = X(p, T) — Ku(T)] has been plotted versus density in figure 9. It is seen that the influence

of the critical point increases significantly the value

of AX.

B-7 J. Phyi. Chem. Ref. Data, Vol. 6, No. 4, 1977
1174 HANLEY, GUBBINS, AND MURAD

<

0 2 4 6 8 10 DENSITY. mo\/l

Figure 9. Plot of ihe calruIateH excess thermal conductivity coefficient, using equation (10). al .305.7 K. 310 K, and 400 K.

Viscosity Coefficient

Although it has been suspected for a long time that the viscosity coefficient of a pure fluid displays anoma-

-lous behavior in the critical region, the magnitude and

quantitative features of tlie anomaly are still under

investigation but it is generally conceded that any anomalous behavior of the viscosity is much weaker

than the corresponding behavior of the thermal conductivity. Recently, however. Strumpf, Collings and

Pings investigated experimentally the viscosity of ethane in the vicinity of the critical point [21]. Tlicy

report an anomalous increase in the viscosity of about 16% if AT < 0.002.S and ^p < 0.25. Further, the results agree with tli_eoretical predictions [34] that ^-qj

Tjlback) = A In AT, where Tjtback) is the viscosity in the absence of anomaly, and A' is a constant which has a numerical value of ap[)roximately 0.034. There seems

little doubt that Strumpf, (lollings, and Pings have

verified quantitatively the existence of a critical point

anomaly in the viscosity of ethane. Unfortunately, from

our viewpoint, the absolute values of the coefficients are uncertain. It turns out that the coefficients away

the critical point differ systematically by 5-10% from

those of Carmichael and Sage [8], and of the other authors considered here. The latter results are higher

at a given temperature and density. Possible reasons

for the discrepancies are discussed in reference [21]. Accordingly, in view of the discrepancies, and since

the data of reference [21] cover a limited experimental

region, the data were excluded from the correlation.

4. Tables of Values

The viscosity and thermal conductivity coefficients of ethane have been calculated for 200—300 K for pressures up to 50 MPa ( =500 atm) and from 300-

500 K for pressures to 75 MPa. Tabular values are presented as tables 4 and 5. We ensured that an entry

in the table would not require an extrapolation beyond

the range of data, with the exception that the lov^ temperature-high pressure thermal conductivity coeffi- cients required our generated saturated liquid values from the excess function. Gaps in the tables at low temperatures indicate that these P-T points correspond

to densities exceeding 17 mol/1; the upper density limit for the data. For convenience saturated liquid values have been listed separately as table 6. (The tables contain more significant figures than the accuracy of the data warrant. The extra figures are given to facilitate reproduction and interpolation of the tables.)

4.1. Uncertainty of the Tables We have been able to fit the data to within their estimated accuracy. The tabular values are judged to have an uncertainty of ±5% for the viscosity coefficient and ±8% for the thermal conductivity coefficient. These estimates of uncertainty refer to an estimate of accuracy on a 2cr basis. Here cr is based on the following: the scatter of the experimental data, deviations between

the data and our correlation, an assessment of the data according to the criteria of referetice [1] and, finally, our experience of evaluating similar data tor other simple

fluids. Close to the critical point, the estimated uncertainties are increased to ±10% for the viscosity coeffi- cient, and ±20% for the thermal conductivity coefficient.

5. Conclusion

The viscosity and thermal conductivity coefficient data for ethane over a wide temperature and pressure range have been represented by an empirical function. Tables of values have been prei)ared. Our assessment and evaluation of the results has been handicapped by

lack of reliable data. A significant improvement requires

(a) data for the dilute gas over a wide temperature

range, e.g., about 200-1500 K, particularly for the

viscosity coefficient, (b) viscosity data for the saturated

liquid from the triple point (90.35 K) to 200 K, and

(c) thermal conductivity data for the saturated liquid over the whole temperature range. It would also be

hei[iful if the more recent technicpies, e.g., those using

the torsional oscillating crystal for the viscosity [1], and the transient hot wire method [2], could he applied

to ethane.

J. Phyi. Chem. Ref. Data, Vol. 6, No. 4, 1977 B-8
TRANSPORT PROPERTIES FOR ETHANE

Tabu. 4. ViMDsity CDefrjiient cif elharie Oir variims l^m(lcralurc^ (K.) and [ire^sures (Ml'a). I'hc units are fijz/li m-^)

1175

T, K 1.0 2.5

67. 2

7 1.

1 OV 7.1

235*

7 8.2 79.9

250. 79.7 91.2 83.7 791..

802.% 809.8 917.0 82"..831.2 «%>t.9

255. Bl.l 92.

85.0 7V&.6 75"..

762.5 776. 1 777.7 785.0 799. J

260. 82.5 »<>.l 86. <• 89. <i 70 7.6 716.1 72'..

732.3 71.0.1 755.1

266. Sk.C iS.S 87.7 90.6 660.9 670.1 579.1 687.7 696.1 712.1

270. «5.5 86.9 89. 1 91.8 95.5 62X.0 633. 9 6<>3. 1. 652.6 669.9

275. 87. e SB. <. 90.

93.1 96.5 576.7 588. 1 598. 9 609.1 628.1

290. as. s 89.9 91.9 9<>.l> 97.6 102.0 5<>0.3 553.1 56>i.8 586.3

2SS. 90. 0 91. <• 93. 3 95.7 98.7 102.7 108. 7 50<..3 519.7 5>>3.a

290. 91. 5 92.8 9U. t 97.1 99.9 103.6 108.7 117.6 1.63. 1. <.99.6

295. 93. i 91.. J 96.2 91.

101.2 10<>.6 109.1 115.9 ••07.1. .51.7

399. 9S. 5 9E.8 97.7 99. 8 ia2.i> 105.6 109. 7 115. I> 121..

395.9

T, K 6.0 7.0 S.C 9.0 10.0 15.0 20.0 30.0 1.0.(1 51.0

220. 1176.1. 1188.1199.7 1211.1 1222.6

225. 1116. 1 1127.9 1139.5 115 1.0 1162.3 1217.4

230. 1 059. 2 1071. 0 1082.

109<..3 1105.1160.1. 1212.3

235. 1 005.2 1017.

1029. 1 101.0.9 1052.2 1107.2 1158.9

2I.C. 953. 9 966.2 979.2 490. 0 1 001.6 1056.9 1108.

1201..

21.5. 905. 0 917.5 92 9. 8 9V1. 9 953.6 1009. <• 1061.

1156.6

250. 858.1 971. 0 893. 6 995.9 907.9 961.. <> 1316.5 1111.

255. 81 3. 1 826. <• 839. 1. 852.0 86^. 2 921.6 971.. 1 1069.9 115<>. 8

260. 769.6 793.5 796.9 80 9. 8 822.5 930.9 933.8 1028.7 1111..

265. 727.1. 711I.9 755.9 769.3 7J2,3 91.2.1 895.6 990.6 1075.5 1153.6

270. 686.2 701.6 716.2 730.2 71.3.7 605.1 859.2 95H.5 1039.0 1116.1.

275. 61.6. 7 66 2.1 677.6 692.

706.5 769.6 92<.. 6 920.3 laofc.i. 1081.1

280. 605.6 623. <• 61.0.0 655.6 670.3 735.6 791. 5 987.7 971.6 101.7.

295. 565.6 585.1 683.0 619.6 636.2 702.9 769.9 856.7 91.0. ^ 1016.0

290. 52U. 9 5J>6.8 566. « JK..3 fcaa.9 671.1. 729.6 827.2 910.7 995.9

295. 1)82. 8 508.1 S3*. 1 M.9 6*7. 4> 61.1.2 700.7 799,1 882. 5 957.2

300. ••38.0 '•6 8.S <.43.b 515.

612.0 673.9 772.3 855.7 929.9

J. Phyt. Chem. Ref. Dolo, Vol. 6, No. 4, 1977 B-9
1176 HANIEY, GUBBINS, AND MURAD

T*BI>; 4. Visrosttv coeffii'ienl eif ethane for variuus lemperatures (K) and pressures (MPa). The units are ;if/(rm.s)—(^cintinued

T, K .1 .5 1.0 1.5 2.0 2.5 3.0 3.5 *.a s.o

300. 95.8 97.7 9 9.0 102.1. 105.6 109.7 115.* 12*.

395.9

310. 97.5 90.0 loa.b 10 2.6 105.0 107.9 111.* 115.

121.9 1*9.5

320. 100.5 101.7 103. > 10 5.<> 107.

110.2 113.3 117.1 121.9 136.5

330. 10 3. 5 10<>.7 106. 3 lOO.l iia.2 112.6 115. * lis. 7 122.6 133.5

3<>0. 106. > 107.6 109. 1 110.9 112.9 115.1 117.7 120.6 12*. 0 132.9

3sa. 109. 3 110.

111. 9 113.6 115.5 117.6 119.9 122.6 125.7 13 3.2

3611. 112.2 11 3.2 111.. 7 116.3 118.1 120.1 122.3 12*.7 127.5 13*.

370. 115.116.0 117.1. 119.0 120.7 122.5 12*. 6 126.9 129.5 135.5

380. itr. ts IIS.R 120. 1 121.6 123.2 125.0 127.0 129.1 131.5 137.0

390. 120.5 121.5 122.

12I..2 125.0 127.5 129.3 131. <i 133.6 139.6

fcOS. 123. 2 12'..125. 1. 1?6, a 129.3 129.9 131.7 133.6 135.7 1*1.*

klO. 125.9 126.0 120. fi 129.1. 130.0 132.* 13*.

135.9 137.8 1*2.2

>>2«. 120.5 129.* 133. 6 131.9 133.3 13*. S 136.* 130. 1 1*0.0 l**.l

<>30. 131. 1 132.0 133.2 131..'. 133. 7 137.2 130. 7 1*0.* 1*2.2 1*6.1

«<>a. 133. 7 13<..6 135-. 7 136.9 139.2 1J9.6 1*1.1 1*2.6 1**.3 1*9.0

<iSO. 136. 2 137.1 130. 2 139.3 11.1.6 1*1.9 1*3. * 1**. 9 1*6.5 150.0

<.60. 130. 7 139.5 11.0. 6 111 1.7 11.3.0 l*i..3 1*5.6 1*7.1 1*9;6 152.0

k70. 1^1.2 1I.2.0 1<.3. 0 1 1*5.5 1*6.5 1*7.9 1*9. 3 150.9 15*.

•SC. 1^ 3. 6 10«.3 1<.5. 3 11.6. > 11.7,6 1*9.0 150.1 151.* 152.9 156. 0

•9Q, 11.5. 9 1^6.6 1*7.6 11.8.7 11.9.9 151.0 152.2 153.5 15*.

157.9

500. l<>e. 1 m8.9 11.9. e 150. 9 151.9 153.1 15*.

155.6 156.9 15 9.0

T, K 6.0 7.0 8.0 9.0 10. 0 15,0 20.0 30.0 50.0 75,0

300. *39. 0 *68.5 *93.* 515.0 53*.* 0.0 0.0 0.0 0.0 0.0 310. 32*. 8 392,0 *17.9 **5.9 *69,* 556.5 0.0 0.0 0.0 0.0

320. 176. 9 273.7 335, 7 375, 1 *05.1 50*.

0, 0 0.0 0.0 0.0 330. 152.5 192.5 251,7 303.2 3*1.6 *56,2 529.6 0.0 0.0 9.0

3*0. 1'.6. 0 167.5 201. 8 2*3,* 293.5 *11.2 *S7. 8 0.0 0.0 0.0

350. 1*3. 6 158.* 180. 0 20 9,6 2*0. * 370.2 *5a.5 561.3 0.0 0.0 360. 1*2.9 15*.

169. 8 190. 0 21*. 1 333,9 *16.6 529.1 0.0 0.0 370. 1*2.9 152.* 16*.

179. 9 199.2 303.2 396. > *99.7 0.0 0.0

300. 1*3. 6 151.7 161. 7 17*.

199.6 278.5 359. 0 *72.9 0.0 0.0

39J. I**. 6 151, 9 160.* 170,6 )92. 6 259.5 335.5 **e.5 0.0 0.0

*oc. 1*5. 9 152.3 159, 8 169.6 174.8 2*5.1 315.* *26.3 577.* 0.0

<.10. 1*7. 3 153.1 159.9 167.6 176, 5 23*.

296.5 *i&.3 5-5.7 0,0

*20. 1*8. 8 IS*.

160. * 157.3 175.1 226.0 28*.

388.3 535.7 0.0

<>30. 150.5 155.5 161. 1 167.* 17,.* 219.7 273.1 372.2 517.2 0.0 **0. 152. 2 155.9 16

167.9 17*,215.0 263, 8 357.8 500.1 0.0 *50. 15*. 0 159.3 16 3.2 159,5 17*.* 211.* 256.1 3*5.1 kS*.3 0.0 *60. 155. 7 159.9 16*. * 169,* 17*. 8 209.6 2*9. 9 333.9 *69.7 595.7

«.T0. 157.6 161.5 165.7 170,* 175.5 206.6 2**. 7 323.9 *56.2 581.2

*SD. 15 9.* 163.1 167. 1 171,5 176.2 205. 1 2*0. 5 315.2 **3. 7 566.6 *9a. 161. 1 16*.

169.5 172.7 177. I 20*.

237.0 307.6 *32.1 552.9

»B0. 162, 9 166.3 169.9 173.9 178,1 203.3 23*. 1 300.9 *21.* 5*0.0

i. Phys. Chem. Ref. Dato, Vol. 6, No. 4, 1977 B-10
TRANSPORT PROPERTIES FOR ETHANE

Tabi^ 5. Thermal conductivity of fthane for various lemperaiures (K) and pressures (MPa). The units are rnW/(m"K)

1177

T, K .1 .5 1.0 1.5 2.0 2.5 3.0 3.5 1.. 0 5.0

2c:. 12.78

zo;. 13.17

210. 13.56

21'. 13.97 l'.5.23 11.5.77 l'.6.3l 11.6.85 11.7.38 11.7 91 11.8. 1.3 11.8.95 11.9.98

zzo. l>>.<-0 1 38 .51. 139. ce 139.62 11.0.15 11.0.68 I'.l 20 . 11.1.72 11.2.23 11.3. 21.

2?5. 1<..«3 17.10 133.17 133 .70 131.. 21. 131.. 76 135 29 135. 80 135. 32 137.33

230. 15.28 17.1.9 127.86 123.1)1 128.95 129.1.8 130 0 1 130.53 131. 05 132.06

235. 15.71, 17.89 123.03 123 .59 121.. 15 121.. 69 125 23 125.76 125.2 9 127.32

21.:. 16.21 13 .31 118.57 119 15 119.73 120.29 120 85 121. 1.0 121. 91. 122.99

2>.5. 16. 69 18.73 20.65 111. 98 115.59 116.18 116 76 117.33 117.89 118.99

250 . 17.18 19.17 21.0 3 Ill 00 111.65 112.28 112 89 113.50 111..0 9 115.23

25 5. 17.(8 19 . 61 21.1-2 107 11. 1 C7. 8 3 108.51 109 17 109.82 110. 1.1. 111.66

260. H.20 20 .07 21.82 23 .58 101.. 07 101..81 105 5 3 106.23 105.91 108.21

265. 19.72 20.51. 22.21. 23 91 103.27 101.10 101 91 102.68 103. 1.2 101.. 83

270. 19.25 21.02 ZZ.bJ 21. .27 26.13 97.31 98 22 99.09 99.92 101.1.8 2T5. 19.79 21.51 23.11 21. 65 26.38 93. 3S 91. 1.0 95.1.0 96. 31. 98.0 9

2!0. 20.31. 22.0(1 23.56 25 01. 26.67 28.78 90 37 91.55 92. 61. 911.51.

2«r

20.90 22.52 21.. 02 25 1.6 27.00 28.99 31 86 87.50 SS. 80 91.10

29r, 21.1.8 23.01. 21.. 50 25 88 27.35 29.0 8 31 52 36.1.8 e^.82 87.1.8

295. 22.0 5 23.57 21.. 99 26 32 27.72 29. 33 31 I.I. 31.. 85 80. 85 83. 87

^00. 22. ai> 2i>.ll 25.1.9 26 78 28.11 29.62 31 50 31.. 21 39.25 80 . kO

T, K 6.5 7.C 8.0 9.

P,

il

MPo IJ.O 15.0 20. 0 30.0 1.0. 0 50.0

11-1.. 21.

138.32

1 33.C6 128.33

121.. 02 120.05

116.3k

112.82

109.1.5

105.17 102.93

99.70

96.1.3 93.12

89.76

86.1.2

83.18

11.5.22 139.29

131.. 03 129.31

125.0 3 121.0 8

117.1.1 113.95

110.63

107.1.3

101.. 29 101.18

98.07

91.. 91. 91.79

88.65

85 .59

11.6.19

II. 0.25

I 31.. 99 130.28

126.01

122.09

118. US 115.03

III. 77

108.61. 105.58 102.59

99.5 9 96.60 93.61

90.61. 87.73

1»7 .15

11.1.19 135.93

131.22 126.97

123. l>7

119.1.6 115.07

112.86 1C9.79

106.81 1C3.89

101.01

93.11.

95. 28

92.1.6 89.67

1-.8.09

11.2.12

1 36.85 132.15

127.90

121.. 02

123.<>i>

117.09 113.92

110.90 107.98

105.13

102.31.

99.5 8 96.83

91.. 11

91. ki.

0. Go

11.6.58

11.1.27 136.55 132.33

128.50

125.00 121.76

118. 7.

115.90

113.20

110.61

108.11 105.68

103.31

100 .99 98.72

o.oc 0.00 1-5.38

11.0.63

136.1.0 132.59

129.12

125.95

123.01

120. 2 7 117.69

115.21. 112.91 110.67

108.50

lOfc .1. I

101.. 37

0.00

0.00

0.00

0.00

11.3.77

139.92

136.1.6

133.32

130.1.5 127.80

125. 3»

123.01.

120. 88 118.83

116.88

116.01 113.22

0.00

0.00

0.00

0.03

0. 00

0.00

0.00

139. 80 136.93

131.. 31 131.89

129. 65 127.56

125. 6D 123.76

122. 00

128. 33

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

o.oo

11.0.11.

137.73

135.51

133.1.5

131.51.

129.71.

128.0 5

126.1.5

, , J. Phyi. Chem. Ref. Data, Vol. 6, No. 4, 1977 B-11
1178 HANLEY, GUBBINS, AND MURAD

Tablk 5. Thermal condurtivily of ethane for various temperatures (K) and pressures (Ml'a). The units are mW/(m»K)—Continued

P, MPo

T. K .1 .5 1.0 1.5 2.0 2.5 3.0 3.5 •>.o 5.0 300. 22. 61. ZS.ll 25.1.9 26.7 8 28.11 29.62 31.50 31.. 21 39.25 80.^4

310. 23.95 25.23 26.53 27.73 28.96 30.29 31.86 33.66 36.68 51.35

320. 25.09 26.39 27.61 28. 7» 29.87 31.07 32.1.3 31.. 01. 36.18 <.i.73 330. 26.37 27.60 28.75 29.80 30.85 31. 9* 33.11. 31.. 1.9 36.11 1.0. 61

31.0. 27.69 2«.8i> 29.93 30.92 31.89 32.89 33.96 35.11. 36. ".7 39.89

350. 29.05 30.13 31.16 32.09 32.99 33.92 31.. 88 35.92 37.06 39.91

360. SO.ki. 31. k6 32. 1.3 33. 3C 31.. 15 35.01 35.88 36.81 37.91 <4.10

370. 31.86 32.83 33.75 31.. 57 35.37 36.16 36.97 37.80 38.69 1.0.66

380. 33.32 3<..2i> 35.10 35.88 36.63 37.37 38.12 31.68 39.66 1.1.61

390. 3>>.82 35.6 8 36.50 37.21. 37.91. 38.61. 39.33 ^O.Oi. 1.0. 76 1.2.31

^00. 36.3*. 37.16 37.91. 38 .6^ 39 .30 39. 95 1.0 . 6 0 1.1 . 93 ^3 .33

kit. 37.89 39.67 39.1.1 1.0.17 1.0.70 >1.31 1.1.92 1.2.51. 1.3.16 %<..1.V

ItZO. 39.1.7 1.0.21 1.0.91 1.1.51. 1.2. l<i ".2.72 ^^.29 1.3.87 1.5. 6S

<>30. >>1.07 1.1.78 1.2.1.5 1.3.01. k3.61 1.1.. 16 41.. 70 1.5.25 1.5.79 1.6.90

<tl>0. 1.2.69 1.3.37 I.1..01 I.I..58 1.5.12 1.5. 6% 1.6.15 1.6.67 1.7.16 1.6.22

<|l..3>> •.•..98 1.5.59 1.6.11. 1.6.65 1.7.15 1.7.61. k«.12 <.«.61 •.9.58

<>60. kS.OO 1.6.62 1.7.20 t.7.72 1.8.21 1.8.69 1.9.15 1.9.61 sg.0 7 50.99

<i7C. W7.68 1.8.27 1.8. 83 1.9.33 1.9.79 50.25 50.69 51.13 51.56 52.^1.

I>8C. l>9.37 ••9.9<i 50.1.7 50 .95 Sl.be 51.83 52.26 52.67 53.09 53.92

kQO

,

51.08 61 .62 52.1% 52.59 53.02 53. 1.1. 53.81. 511.21. 51.. 6>. 55.1.3

SCO. 52.80 53.32 53.81 51.. 25 51.. 67 55.06 55.1.5 55.83 56.21 56.96

T, K 6.0 7.0 8.0

P, 9.0MPa 10.0 15.0 20,0 30.0 50.0 75.0

303. 83.11 85.59 87.73 ^9.67 91 0.00 0,00 9.00 0,00 0.00

3i:. 77. CI 79.91 82.31. 8-.. 1.7 86.1. 1 9-. 31. 0.00 0.00 0,00 0.00

3ZC. 58.30 72.1.7 76.9'. 79.69 81.89 90.27 0,00 0. 00 0,00 0,00

330. >a . lb 59.12 68.28 73 . 7b 77.13 86.61 93,30 0.03 0,00 0.00

31.3. i.,.79 51.62 59.19 t5.77 7J.9a 83.18 90.16 O.OQ 0,00 0,00

350. 1.3.1.2 1.8.12 53.67 59.2". ei..3i 79.62 87.21. 98.20 0.00 0.00

36C. 1.2.95 kb.iiS 50.58 ?5.02 59.39 75.78 81.. 1.0 95.76 0.01 0.00

371. 1.2.99 1.5.75 1.8.91. 62.1.6 56.09 71,90 81.55 93. k9 0.00 0.00

38 0. ^3.38 1.5. 61. 1.8.21 51.01. 61.. 01. 68.1.1. 78.71 91.36 0.00 0.00

390. l.'..02 h5 .93 1.8.06 60.39 52.89 65.70 76.05 89.31. 0.00 0.00

•JO. "..Oi. 1.&.50 1.8.32 50 .29 52,1.0 63,72 73.71 87. ••4 10^.67 t.oo

".10. 1.5. 81 1.7,29 1.8.86 50.56 52.38 62.1.0 71.81 85.69 103.23 O.OQ

tzc

1.6.89 •8.21 1.9.62 51.12 52.71 61.61 70,36 81.. 13 101,91 0.00

<.J0. 1.8.05 ••9.26 50.53 51 .88 53.30 61 .26 69,35 82.81. 100,71 a. 00

l-<>0. k9.29 50.1.0 51.57 52.79 5-.. 07 61.26 68,73 81. 7C 99.61. 0.00

•.50 . 50 .56 51.62 52.70 53.82 6<..99 61.51 68,1.2 80. at. 99.69 0,00

<.ei<. 51.93 52.90 53.90 51.. 91. 56.01 61.98 68,38 80.21 97.96 113,60

•70. 5J.33 51.. 23 55.17 56.13 57.13 62.62 68,56 79.80 97.16 112.87

keo. 51.. 76 55.61 56.1.9 57.39 58.32 63.1.0 68,92 79.57 96.59 112.22

«.9C. f6.22 57.03 57.86 58.71 59.58 61., 3C 69, 1.1. 79.53 96.11, 111.67

rCC. 57.72 S8.1.8 59.26 60.06 60.88 65.29 70.0? 79.61. 95.61 111.20

J. Phyi. Chom. Ref. Dato, Vol. 6, No. 4, 1977 B-12
TRANSPORT PROPERTIES FOR ETHANE 1179

TABLES. VISCOSITY tNQ ThERM»L COIlOUCnvITT COEFFICIENTS OF S«TUI>«TED LIQUID ETHtNE.

oensitt viscosity therk»l conouctivity

MOLES/L HICRO-C/(CH»S» HILL1-M/(H»K»

13S9.9 172.0

ir.23S 1313.1 161. 6 17.009 12<il.i> 152.

16.77* 117"..

1<|5.3

16.S<il 1111.2 1 138.7

ie>.29« 1051.5 132.9

16.D>>% 995.1 127.7

15.7Sk 9<>1.V 123.0 15.51V 990.1 119.7

15.233 0<il.O 11<>.7

1<>.939 793.0 110.9

1<>.631 7lit.l 107.3

1V.306 703.0 103. 7 13.961 660.6 100.2

13.592 61S.2 96. 8 13.193 576.3 93.3

12.755 53>..i> 99.8 12.265 192.1 86.

11.702 <•<•«.

83.2

11.021 <>01.5 80.5

10.105 3>>7.3 78.8

a. 073 2Slt.7 95.1

KELVIN

200.

205.0 210.0

215.0

220.0 225.0 230.0

235.0

2<i0.0

2<.5.0 250.0

255.0 260.0

265.0

270.0

275.0

280.0

2 95.0 290.0

295.0

300.0

305.0

6. Acknowledgments

H. Hanley was supported by the Office of Standard Reference Data. K. Gubbins and S. Murad were sup- ported in part by the American Gas Association.

References

[1] Hanley, H. J. M., McCarty, R. D., and Hayncs, W. M., J. Phys. Chem. Ref. Data 4-, 979 (1974). [2] Hanley, H. J. M., Haynes. W. M., and .McCarty. R. D., J. Phys. Chem. Ref. Data 6, 597 (1977). [3] Hanley, H. J. M., McCarty, R. D., and Hayncs. W. .M., Cryogenics 15,413 (1975). [4] For example: .Makila. T.. Tanaka. Y., and Napashima. A.. Rev. Phys. Soc. (Japan) 44, 98 (1974); Calloway, T. R., and Sage,

B. H., J. Chem. Enj;. Data 12, 59 (1967); Rossini, F. D., Pitzer, K. S., and Taylor. W. J., Nal. Bur. Stand. (U.S.) Cir. C-461 (1947); Vargaftik, N. B., Filippov, L. I'., Tarzimanov,

A. A., and Yurchak, R. P.. "Thermal Conductivity of Gases and

Liquids." Moscow (1970); (iohibev. 1. F., "The Viscosity of Gases and Gas .Mixtures." Israel Program for Scientific Translations, Jerusalem (1970) (available from the LIS. Department of Commerce); (iuereca, R. A., el al., "Thermophysical Properties of Selected (>ases Below 300 K." Bureau

of Mines Cir. 8317 (1967); "Thermophysical properties of matter," Vols. 3 and 11. IFI/Plenum, New York, 1975. Eds.

Y. S. Touloukian, S. C. Saxena and P. Hestermans.

[5] See the references in [1].

[6] (;oodvsin, R. D., NBSIR 74-398 (June 1974). [7] Eakin, B. E., Starling, K. E., Dolan. J. P., and Ellington. R. T.,

J. Chem. Eng. Data 7, 33 (1962).

[8] Carmichael, L. T., and Sage. B. H., J. (;hem. Eng. Data 8, 94

(1963). [9] De Rocco, A. G., and Halford. J. O., J. Chem. Phys. 28, 1152

(1958).

[10) Vogel, H., Ann Physik, 43, 1235 (1914).

[11] Trautz, M.,andSorg. K. <;.,Annl'hysik 10,81(1931).

[121 Adzumi. H., Bull. Chem. Soc. (Japan) 12,199(1937).

[13] Lambert. J. D., Cotton, K. J., et al., Proc. Roy. Soc. (London)

231A,280(19.S5).

[14] Craven. P. M., and Lambert, J. D., Proc. Roy. Soc. (London) 205A, 439 (1951).

[15J Kestin. J., Ro. S. T., and Wakeham, W. A., Trans. Faraday Soc. 67,2308(1971).

[16) Ishida,Y.. Phys. Rev. 21,550(1923).

[17) Titani.T., Bull. Chem. Soc. (Japan) 5,98(1930).

[18) Gcrf. S. F.. and Galkov, G. 1., Zhur. Tekh. Fiz. 10, 725 (1940); 11,801 (1941); 11,613(1941).

[19] Swift. G. W., Loreni, J. and Kurata, F., AIChE J. 6, 415 (1960).

[20) Baron. J. D.. R,.of, J. G.. and Wells, F. W.. J. Chem. Eng. Data 4,

283(19.59).

[2!) Strumpf, H. J., Collings, .\. F. and Pings, C. J., J. Chem. Phys. 60,3109(1974).

[22) Le Neindre, B., Ph.D. Thesis, Univ. of Paris (1969).

[23) Keys.F.(..,Trans. Am. Soc. Mech. Engs. 75,809(1954).

[24) Eucken. A.. Physik Z. 14,342(1913).

[25) Lenoir, J. M., and Comings, E. W., Chem. Eng. Progr. 47, 223

(1951).

[26) Lenoir, J. M., Junk. W. A., and Comings, E. W., Chem. Eng.

Progr. 49,.539(19.53).

(271 (iilmore, T. F., and Comings, E. W., AlChE J. 12, 1172 (1966).

[28| Zeigler. Dissertation, Halle liniv., 1904, International Critical Tables. 5,212, McGraw-Hill, New York (1929).

B-13 J. Phys. Chem. Ref. Data, Vol. 6, No. 4, 1977
1180 HANLEY, GUBBINS, AND MURAD

{2')\ Miiser. Ph.D. Thesis, Berlin Univ.. Internuticmal ("ritiial Tables. 5,212. Mc(;raw-Hill, New York (1929).

(30| Carmichael. L. T., Berry. V., and Sa-e. B. H., J. Chem. En-. Data 8,281 (1963).

[311 (luevara. F. .\., .Mclnteer, B. B., Otiesen. D., and Hanley. H.J. M., Los Alamos Publ. No. LA-4643- VIS (1971).

132) For example. Ely. J. F.. and Hanley, H. .1. M.. .Molec. Phys, 30,

565(1975).

1.331 Hanley. H. .1. M.. Senders, ,1. V.. and Ely,.I. F., 14lh Int. Conf. on Thermal Conductivity (Storrs, Conn., June 1975) Klemens,

P. G., and Chu. T. K., Eds. (Plenum Press N.Y.. 1976) p. 383.

(341 Sengers, .1. V., in "Transport Phenomena— 1973." (AIP, New

York, 19731, Kestin, J., and Ross, J., Eds., p. 229.

J. Phy». Chem. Ref. Dafa. Vol. 6, No. 4, 1977 B-14
R-1014

M-700

J. Chem. Thermodyn. Vol 9, No. 2, 179-87 (Feb 1977)

Measurements of the orthobaric liqiiid

densities of metharse, ethane, propane,

isobiiiane, and normal butane *

VV. M. HAYNES and M. J. HIZA

Cryogenics Division, National Bureau of Standards,

Institute for Basic Standards, Boulder, Colorado 80302, U.S.A.

{Received 9 August J 976)

The orthobaric liquid densities of the major components of natural gas have been deter- mined with a magnetic suspension densimeter. This paper reports results for methane

(105 to 160 K), ethane (100 to 270 K), propane (100 to 288 K), isobutane (1 15 to 300 K),

and normal butane (135 to 300 K). The imprecision of the measured densities is approximately 0.015 per cent; the estimated overall uncertainty is O.I per cent at low temperatures

and decreases to 0.06 per cent at 300 K. A simple expression has been used to represent

the densities as a function of temperature. Comprehensive comparisons witli tiie e>;peri- mental results of other investigators are presented.

1. Introduction

Liquefied natural gas (lng) is expected to become an increasingly important commodity on the world energy market. The basis for sale of lng is its total heating value,

which requires a knowledge of both density and composition. A project was initiated at this laboratory to provide orthobaric (saturated) liquid densities for the major

components of lng, and for mixtures of these components. The densities will be

used to develop a mathematical m.odel or correlation that predicts the density of

LNG type mixtures with an inaccuracy of 0.1 per cent, given a knowledge, of the

composition and temperature of the liquid. In the development of an accurate mathematical model (correlation), it is important to have both an accurate and an

internally consistent set of density data. Before this project was started there were significant temperature ranges for which saturated (orthobaric) liquid density data did not exist for some of the major

components of lng. For nitrogen and methane there were discrepaiicies as large

as 0.5 per cent between different sets of data. Not only was it important to fill in

" This work was carried out at the National Bureau of Standards under the sponsorship of

British Gas Corp., Chicago Bridge and Iron Co., Columbia Gas Service Corp., Distrigas Corp., Easco Gas LNG, Inc., El Paso Natural Gas, Gaz de France, Marathon Oil Co., Mobil R&D Corp., Natural Gas Pipeline Co., Phillips Petroleum Co., Shell International Gas, Ltd., Sonatrach, Southern California Gas Co., Tennessee Gas Pipeline, Texas Eastern Transmission Co., Tokyo

Gas Co., Ltd., and Transcontinental Gas Pipe Line Corp., through a grant administered by the American Gas Association, Inc.

C-1
180 W. M. HAYNES AND M. J. HIZA

gaps, but also to provide new independent measurements of sufficient accuracy to help resolve inconsistencies. In this paper orthobaric liquid densities for methane, ethane, propane, isobutane,

and normal butane are reported. Results for nitrogen were presented in an earlier paper.'" Major emphasis has been placed on the low temperature region of 105 to 140 K; however, measurements have been carried out to 160 K for methane, to 270 K for ethane, to 288.7 K for propane, and to 300 K for isobutane and normal

butane. The densities have been- represented as' a function of temperature with an

expression that is used to facilitate comparisons with other measurements.

The present measurements were carried out with a magnetic suspension densi- meter.'" In this method a magnetic buoy is freely suspended in the liquid of interest by the force generated from the axial magnetic fields of air-core solenoids. The

motion of the buoy is controlled by the automatic regulation of a servo-circuit. The magnetic force necessary to maintain the buoy at a given position is inversely

proportional to the buoyant force on the buoy. Thus, using Archimedes' principle,

along with measurements of the mass and volume of the buoy, the density of the

liquid is obtained.

2. Experimental

The experimental apparatus and its operation have been described in detail else- where.'" At low temperatures the experimental procedures for the measurements on

the hydrocarbons other than methane differed significantly from those for nitrogen

and methane. The density of a given fluid is determined from measurements of the magnetic force necessary to support a barium ferrite buoy in a vacuum and in the

fluid at the same position and temperature. For nitrogen and methane the vacuum

measurements were performed immediately before or after the liquid measurements.

At low temperatures it has been found impossible to evacuate the sample cell within

a reasonable time after" it has been filled with one of the heavier hydrocarbons. Most

of the liquid can be removed by pressurizing with helium gas; however, a liquid film is left on the surfaces, including those of the buoy, inside the cell. The buoy

cannot be brought into support until the film is removed. Thus, for the heavy hydrocarbons at low temperatures, the vacuum points must be obtained before the liquid

measurements.

So that more than one point could be obtained in a given day for a heavy hydrocarbon at low temperatures, vacuum points were obtained at two temperatures

separated by 5 K before liquid was condensed into the cell. Then the liquid measure- ments were performed at each of these temperatures. Performance tests had demonstrated that the barium ferrite buoy does not exhibit any detectable hysteresis at low temperatures within the precision of the current measurements for a temperature

range of, at least, 20 K. After the vacuum and liquid measurements were performed for one of the heavy hydrocarbons at low temperatures the cell was warmed to a temperature above the normal boiling temperature of the test fluid for evacuation.

Methane v/as used as a control fluid during the heavy-hydrocarbon measurements

at low temperatures. Each day a new methane point was taken to insure that the

C-2
LIQUII) DENSITllZS OF CH^, QHo, CoHe, /-C,Hi„. AND «-C«H,o J8I warm-up and cool-down of the apparatus did not afTcct the apparent position of the

buoy from liquid-to-vacuum measurements. The position of the buoy was deter- mined with a high-powered microscope that had been adjusted initially so that the apparent position of the buoy did not idcpcnd on the index of refraction of the fluid inside the cell. It was found that the temperature cycling of the cell had no detectable

effect on the apparent buoy position.

Some of the results presented in this paper were taken with a one-coil system

instead of the three-coil arrangement described in the apparatus paper.^*^ The evolution to the use of only one coil is discussed in reference 2. All of the gases were of research grade quality. The minimum purities as specified

by the suppliers were 99.9 moles per cent for isobutane and normal butane and

99.99 moles per cent for methane, ethane, and propane. The gases were analyzed

chromatographically with a thermal-conductivity detector and found to be within

the specified purities except for isobutane. It was found that the isobutane contained

approximately 0.15 per cent of normal butane. This relatively large amount of normalbutane impurity has a negligible effect (< 0.01 per cent) on the density results. The methane gas was passed through a room-temperature m.olecular-sieve trap

to remove moisture and any heavy contaminants not detected by analysis. The

other hydrocarbon gases were normally not passed through a molecular-sieve trap.

3. Results

The experimental orthobaric liquid densities of methane, ethane, propane, isobutane,

and normal butane are presented as a function of temperature (IPTS-68) in tables

1 to 5. The relatively large number of points for methane at any given temperature

resulted from the use of methane as a control fluid throughout the project. Although

the mean experimental densities of methane have been given in an earlier paper^**

they are presented again here, along with other information (calculated densities,

etc.), so that the orthobaric liquid densities of all the low molecular-weight alkanes

TABLE I. Orthobaric liquid densities of methane, where T is the temperature (IPTS-68), pexpt is the incan experimental density for n observations at a given temperature, Pcnic is the density

calculated from equation (1) and zl^ar is the largest value of (/^expt — Pck^c)IPc<i\c

T/K /7expt/mol dm~^ II Pcaic/mol dm ^ lO^Jn^ax

105.000 26.9458 12 26.9456 0.030

110.000 26.4985 11 26.5005 0.035 115.000 26.0443 12 26.0429 0.028 120.000 25.5721 17 25.5712 0.036 125.000 25.0845 18 25.0839 0.037 130.000 24.5775 16 24.5790 0.036

135.000 24.0540 23 24.0540 0.031 140.000 23.5067 5 23.5060 0.024

145.000 22.9312 5 22.9311 0.024

150.000 22.3218 2 22.3243 0.014

1 fiO.OOO 20.9876 2 20.9857 0.037

13

C-3
182 W. M. HAYNES AND M. J. HIZA

TABLIi 2. Orthobaric liquid densities of clhane, where T is the temperature (II'TS-68), /j„,„t is the experimental density, /;„„i„ is ihc density calculated from equation (I), and A is the value

of (P.xv<. - /'oalc)K«ln

T

K

/'eipt mol dm"*/'oalo molidni"^

1K mol dm"^

A'oalo mol dm "^ lO^zl

100.000 21.3408 21.3388 \009 170.000 18.6867 18.6869 -0.001

105.000 21.1585 21.1568 0.008 180.000 18.2793 18.2787 0.003 110.000 20.9746 20.9742 0.002 190.000 17.8612 17.8586 0.015 115.000 20.7927 20.7907 0.010 200.000 17.4289 17.4240 0.028 120.000 20.6022 20.6063 -0.020 210.000 16.9713 16.9720 -0.004

125.000 20.4186 20.4208 -0.011 220.000 16.4988 16.4989 -0.001

130.000 20.2317 20.2343 -0.013 230.000 15.9973 1 5.9994 -0.013

135.000 20.0461 20.0466 -0.002 240.000 15.4642 15.4670 -0.018

140.000 19.8566 19.8575 -0.005 250.000 14.8899 14.8919 -0.013

150.000 19.4751 19.4748 0.002 260.000 14.2610 14.2598 0.008 160.000 19.0857 19.0850 0.004 270.000 13.5493 13.5477 0.012

TABLE 3. Orthobaric liquid densities oi' propane, where T is the temperature (lPTS-68), p^xpt is the experimental density, /^caio is the density calculated from equation (1), and A is the value

ale

T

K

Poxpt T

K

Pexpl PcaXc mol dm"' IQPA mol dm~^ mol dm"' mol dm~^

100.075 16.3065 16.3048 0.011 140.075 15.3751 15.3755 -0.002

105.075 16.1872 16.1885 -0.008 145.075 15.2588 15.2590 -0.002

110.075 16.0718 16.0723 -0.003 150.075 15.1400 15.1424 -0.016

115.075 15.9557 15.9562 -0.003 200.000 13.9560 13.9524 0.026 120.075 15.8411 15.8401 0.006 240.000 12.9271 12.9285 -0.010

125.075 15.7250 15.7241: 0.006 270.000 12.0733 12.0742 -0.008

130.075 15.6085 15.6080 0.003 280.000 11.7622 11.7631 -0.008

135.075 15.4910 15.4918 -0.005 288.706 11.4790 11.4775 0.013

TABLE 4. Orthobaric liquid densities of isobutane, where T is the temperature (lPTS-68), poxpt is the experimental density, /7caio is the density calculated from equation (1), and A is the value of (/'expt — Pca.lc)/Pc<i\c

T

K

PenpX. Pca.\o IQ^A

T

K

Pcalc \(PA mol dm"' mol dm"' mol dm"' mol dm"'

115.075 12.7305 12.7313 -0.006 145.075 12.2353 12.2372 -0.015

120.075 12.6489 12.6491 -0.001 150.075 12.1534 12.1544 -0.008

125.075 12.5687 12.5669 0.015 228.000 10.8273 10.8263 0.009 130.075 12.4850 12.4846 0.003 288.706 9.6676 9.6687 -0.012

135.075 12.4015 12.4022 -0.005 290.000 9.6411 9.6417 -0.007

140.075 12.3215 12.3197 0.014 300.000 9.4300 9.4287 0.014

C-4
LIQUID DENSITIES OF CH„ CaHo, CaHs, i-C^Uio, AND n-dUio 183

TABLE 5. Orthobaric liquid densities of normal butane, where T is the temperature {1PTS-6S),

/Kxpi is the experimental density, /^c^ic is the density calculated from equation (1), and A is the value of (/'oipt — PcalJZ/'oalo T

K

10^J

T

K

Pcalo 10"J

mol dm"^ mol dm"-* mol dm"' mol dm"'

135.075 12.6517 12.6524 -0.005 165.075 12.1634 12.1659 -0.P20

140.075 12.5706 12.5714 -0.006 170.075 12.0839 12.0846 -0.005

145.075 12.4920 12.4904 0.013 230.000 11.0911 1 1 .0905 0.005

150.075 12.4089 12.4093 -0.003 288.706 10.0325 10.0324 0.001 155.075 12.3299 12.3283 0.014 290.000 10.0067 10.0073 -0.007

160.075 12.2484 12.2471 0.010 300.000 9.8103 9.8099 0.004

investigated in the present work are included in a single paper. All of the experimental

points for methane will be presented in a future report. Each methane point was

taken from a new filling of the cell. For the other hydrocarbons no more than two

points were taken from a single filling. The experimental densities p have been fitted as a function of temperature T to the expression:

(p-p,)/moI dm-^ = a{l-TITJ° '' + ^ b,(l-TITj'^^'''>''\ (1)

which incorporates a scaling-law modification^"*^ to a generalized Guggenheim

equation. The coefikients a, b-^ determined by least squares, and selected values

of the critical temperature and density for each fluid are given in table 6/^~'*^

Only three coefficients were needed to fit the results for methane, which covered a

relati\ely small temperature range compared with that for the other fluids. The residual standard deviations of the fit to equation (1) for each fluid are given

in table 6. These values substantiate the estimate of the imprecision of the density

measurements, Vi/hich is approximately 0.015 per cent. The estimated inaccuracy in

TABLE 6. Parameters of equation (1),

{p - /7o)/mol dm-' = a(l - TjT.f '''' + 2 - 7/7;)" ^"-"">

where 7"c and are the critical temperature and density. The coefficients a, bi, bz, ba were obtained from a least-squares program in which the experimental mass densities to five digits were converted

to molar densities wiihin the program. The standard deviations a and molar masses M are also given

Methane Ethane Propane Isobutane Normal butane

b2

7-e/K Pr.hno] dm ' 10^a/<p>

A//g mol"'

18.65812 6.712030 -0.9472020

190.555<«

10.16"' 0.016 16.04303

12.55205

13.43284 -19.00461

11.07716

305.33

6.86'8> 0.012 30.07012

8.684459

18.04086 -29.46261

16.43559 369.82"'

5.00<9) 0.011 44.09721

7.657535

8.145251 -13.10582

8.145S94

408.13*1°' 3.80"°' 0.013 58,1243

7.286063

11.96308 -19.87592

11.60211 425.16<i"

3.92'"' 0.012 58.1243

C-5
184 W. M. HAYNES AND M. J. HIZA

the densities is O.I per cent at low temperatures and decreases to 0.06 per cent at 300 K. The total uncertainly in the reported temperatures is estimated to be less than

30 mK at 100 K and less than 40 mK at 300 K. These uncertainty limits in the temperature correspond to a maximum uncertainty of 0.02 per cent in the density

for the results reported in this paper. A detailed error analysis of the magnetic

suspension densimeter used in the present work has been given elsewhere.'"

Equation (i), along with the parameters given in table 6, has been used for comparisons of the present results with independent experimental data.'^' ' 2-^^' Deviation

plots for ethane, propane, isobutane, and normal butane are presented in figures 1

0.8

0.6

cx" 0.4

f 0.2

s 0

• -0.2

-0.4

1 r

eV e

e e

o—^^o o o

"

100 140 180 220 260 T/K

FIGURE 1. Deviation plot of experimental orthobaric liquid densities of ethane compared with

values calculated from equation (I) using parameters from table 6. O, present results; ©, Shana'a and Canfield;"2> O, Chui and Canfield;''^' ©, Orrit and Olives;'"' A Rodosevich and Miller ;>'^',

, McClune;"®' O, Klosek and McKin!ey;<"' A, Douslin and Harrison;"^' 0, Maass and

Wright V, Jensen and Kurata;'^"' V, Kahre.'^"

through 4. The deviation plot for methane was presented in an earlier paper;^"

thus, it is not included here. In comparing the. results of other investigators with equation (1) some general

trends are observed. Below 140 K the densities of Shana'a and Canfield,"'' Chui

and Canfield,<*3> Orrit and 01ives,<^'^> Rodosevich and Miller,*' McClune,"^' and

Klosek and McKinley''^^ are generally lower than the present results by 0.05 to

0.1 per cent. Exceptions to this trend are: for isobutane the densities of Rodosevich

and Miller'^^' between 114 and 120 K are larger (maximum of 0.1 per cent) than

the present results and exhibit a significantly different temperature dependence;

and for ethane the change in density with temperature reported by Klosek and

McKinley^'^^ is appreciably larger than that observed in the present work.

C-6
0.4

0.3

0.2

^ 0.1

5 0

-0.1

-0.2

i.iOUiD di:n.sitii;s oi- ciu, c,Ho, ch,,. /-cm,,,, and ii-V,\U„ 185

0.49

1 r 1 r

ee e** e a

« 6

—Q-O-OjLa_Q_

g ^ <B a. «

a 3 " " a D M^o D 0 ° °

°

"T3

<r

100 140 180 220 260 T/K

FIGURE 2. Deviation plot of experimental orthobaric liquid densities of propane compared

with values calculated from equation (1) using parameters from table 6. O, present results; Sliwinski;'^> O, Shana"a and Canfield;"^' ®, Orrit and Olives;'^" A, Rodosevich and Miller;"^' n, McClune;'^^' M, Klosek and McKinley;'"' 0, Maass and V/right;"^) y, Jensen and Kurata;<2o> T, Kahre;'"' ©, Tomlinson;'") Seernan and Urban;'^^^ ®, NGAA;'-^*'; C, Van der Vet.<">

0.3

^ 0.2

0.1

-0.1

\2

120 160 200 240 T/K

280

FIGURE 3. Deviation plot of experimental orthobaric liquid densities of isobutane compared

with values calculated from equation (1) using parameters from table 6. O, present results;

*, Sliwinski;'^' ®, Orrit and Olives;"*' A, Rodosevich and Miller;"^' , McClune;'^°* V,Kahre;<2"

(g, NGAA;'"' ©, Van der Vet.'"'

C-7
186 W. M. HAYNES AND M. J. HIZA

0.3

0.2

0.1

0

-0.1

-0.2120

c ©

160 200 240 280

FIGURE 4. Deviation plot of experimental orthobaric liquid densities of normal butane compared

with values calculated from equation (1) using parameters from table 6. O, present results;

*, Sliwinski;"" 0, Orrit and Olives;''*' , McClune;"^' V, Kahre;"" ®, NGAA;'"' ©, Van

der Vet/2"'

Above 140 K the data of Chui and Canfield/^^^ Oirit and Olives/*'*^ and

McClune^'^' differ from the present results by less than 0.05 per cent. At higher

temperatures (above 280 K) the data of Sliwinski^^' for propane, isobutane, and

normal butane generall}' differ from the present results by less than 0.05 per cent. The orthobaric liquid densities reported by Douslin and Harrison^ for ethane at temperatures betvv'een 248 and 263 K were systematically larger than the present

results by 0.3 to 0.35 per cent. Some of the older less precise (but frequently used)

data have been included on the deviation plots for the sake of completeness.

Although Klosek and McKinlcy^^'^ give densities for isobutane and normal

butane at temperatures between 105 and 133 K, these densities are not experimental,

and therefore, arc not plotted on figures 3 and 4. A few comments on the reliability

of the omitted values are appropriate. Their densities were obtained from the Francis

equation. For normal butane at temperatures below its triple-point temperature,

their results were systematically higher by less than 0.2 per cent than the densities obtained through extrapolation of the present results.^'''' However, their isobutane

densities at temperatures between 116 and 133 K were 1.5 per cent higher than those

of the present v.'ork. ' .

4. Summary

This research has provided accurate and self-consistent measurements of the orthobaric liquid densities of methane, ethane, propaiie, isobutane, and normal butane

at temperatures down to 100 K. Most of the measurements recently reported by

other workers differ from the present results by less than 0.1 per cent. In subsequent

papers, density measurements on liquefied mixtures of the major components of

liquefied natural gas will be reported.

C-8
LIQUID DliNSITiKS OF CH,, CjHs, C,Hu, /-C,ll,u, AND ;;-C,H,o 187

The authors would like to acknowledge R. D. McCarly aud M. J. Browa for assistance

with the correlation and reduction of the data.

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18. Douslin, D. R.: Harrison, R. H. J. Chem. Thermodynamics 1973, 5, 491.

19. Maass, O.; Wright, C. H. /. Am. Chem. Soc. 1921, 43, 1098.

20. Jensen, R. H.; Kurata, F. /. Petrol. Tcchiiol. 1969, 21, 683.

21. Kahre, L. C. J. Chem. Eng. Data 1973, 18, 267.

22. Tomlinson, J. R. Natural Gas Processors Assoc. Tech. Piihl. TP-1, Tulsa, Oklahoma, 1971.

23. Seeman, F.-W.; Urban, M. Erddl und Kohle Erdgas Petrochem. 1963, 16, 117.

24. Tech. Comm., Natl. Gas. Assoc. .4m. Jnd. Eng. Chem. 1942, 34, 1240.

25. Van der Vet, A. P. Congress Mondial dn Petrol., Paris, Vol. !l, 1937, p. 515.

26. Francis, A. W. Ind. Eng. Chem. 1957, 49, 1779.

27. Haynes, W. M.; Hiza, M. J. Advances in Cryogenic Engineering Vol. 21. Timmerhaus, K. D.;

Weitzel, D. H.; editors. Plenum Press: New York. 1976, p. 516.

C-9

llSa)MM - F.RL

M-754

/. Chem. Tlicrnwdynamics 1977, 9, S73-896

Orthobaric liquid densities and excess

volumes for binary mixtures of low molarmass alkanes and nitrogen between

105 and 140

M. J. HIZA, W. M. HAYNES, and W. R. PARRISH

Cryogenics Division, Institute for Basic Standards,

National Bureau of Standards, Boulder, Colorado 80302, U.S.A.

{Received 21 February 1977)

A magnetic suspension densimeter has been used to determine orthobaric liquid densities of gravimctrically prepared binary mixtures of the major components of liquefied natural gas (LNG) i.e. nitrogen, methane, ethane, propane, /-butane, and «-butane, generally between 105 and 140 K. All binary combinations were included in this study, with the exception of nitrogen + ?-butane and nitrogen -f «-butane. Uncertainties in the reported

liquid-mixture densities are discussed in detail. Comparisons are made between excess volumes computed from the present results and comparable values from the literature.

It was found that the volumetric properties of binary liquid mixtures of the heavy hydro- carbons (those mixtures not containing nitrogen or methane) are closely approximated

by ideal mixing. Some observations are included on the use of excess volumes of the heavy

hydrocarbon systems to determine effective molar volumes of /;-butane in liquid mixtures below its triple-point temperature. For mixtures containing nitrogen or methane, approxi- mate total vapor pressures are given.

1. Introduction

Custody transfer of liquefied natural gas (LNG) on the world energy market has

imposed one of the most stringent requirements for accuracy in the prediction of

orthobaric (saturated) liquid mixture densities. Since heating value is directly related

to the density and composition of the liquid, it is desirable to be able to predict LNG

densities within a small known uncertainty, preferably within +0.1 per cent, for any

condition encountered in commerce. The most promising theoretical methods for predicting the properties of fluid mixtures require that the pure-component characteristic parameters be combined to give the mixture characteristic parameters of the included binary pairs. It is well known that small adjustments to these parameters can significantly affect the difference

" This work was carried out at the National Bureau of Standards under the sponsorship of British Gas Corp., Chicago Bridge and Iron Co., Columbia Gas Service Corp., Distrigas Corp., Easco Gas

LNG, Inc., El Paso Natural Gas, Gaz de France, Marathon Oil Co., Mobil Oil Corp., Natural Gas

Pipeline Co., Phillips Petroleum Co., Shell International Gas, Ltd., Sonatrach, Southern California Gas Co., Tennessee Gas Pipeline Co., Texas Eastern Transmission Co., Tokyo Gas Co., Ltd., and

Transcontinental Gas Pipe Line Corp., through a grant administered by the American Gas

Association, Inc.

D-1
874 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

between predicted and actual mixture properties. Though reasonable estimates of

deviations from the combining rules can be made in special cases/'' the best values

for a given application and model must still be derived from accurate and consistent

experimental results at several temperatures for the binary mixtures and pure components of interest. For the development of a model to predict LNG densities reliably, for example, one needs sufRcienlly accurate densities of uniformly high precision for the pure

components and the possible binary combinations, as well as for selected multicomponent mixtures, to test and optimize the prediction method. To provide this data base, a comprehensive study was initiated in our laboratory to obtain orthobaric

liquid densities of the desired accuracy for the major components of LNG and for

their mixtures.

Previously, orthobaric liquid densities were reported for nitrogen^^' and the low

molecular-weight alkanes—methane,*'"' ethane, propane, /-butane, and /?-butane*^''^ —as determined with a magnetic suspension densimeter.

The present study was conducted with the same apparatus to obtain orthobaric

liquid densities for gravimetrically prepared binary mixtures of these components,

generally between 105 and 140 K. All of the possible binary systems were studied,

with the exception of nitrogen -h /-butane and nitrogen -H /z-butanc. Based on the

phase equihbria for nitrogen + ethane*^'''^ and nitrogen + propane*^^^ it was estimated

that the limits of miscibiUty for the nitrogen 4- butane systems would preclude the

possibility of obtaining experimental densities for these systems in the temperature

range of interest. Where possible, total vapor pressures were also determined, but these are considered approximate since the main focus was to assure the reliability of the

density measurements.

Excess volumes, computed for each of the binary mixtures studied, show that

mixtures of the heavy hydrocarbons exhibit nearly ideal mixing. Effective liquidphase molar volumes for n-butajic below its triple-point temperature were obtained

from the ethane -f- 77-butane liquid-mixture densities by assuming that the small

excess volume remains constant in the temperature range studied.

Only a few sets of orthobaric liquid-mixture densities in the literature*^^' provide

data applicable to the LNG problem discussed above. These data are generally

limited in either the temperatures or compositions covered, or have admitted in- accuracies significantly larger than the desired +0.1 per cent. Comparisons are made

between excess volumes from the present study and comparable values taken from

the literature. Prior to the present study, there were no liquid densities in the temperature range of interest for nitrogen + ethane, nitrogen + propane, ethane -I- /-butane,

propane + /-butane, propane + rt-butane, or /-butane + //-butane.

2. Experimental

The magnetic suspension densimeter used in this study was discussed in detail else- where.^^' ''^ All of the results reported here were obtained with the one solenoid

arrangement.^^' With this arrangement a barium fcrrite magnetic buoy of known

mass and volume is freely suspended, in vacuum and in the liquid, by the force

D-2
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 875

generated from the axial magnetic field of a single air-core solenoid. The position

of the buoy is controlled by automatic regulation of the solenoid current with a radio-frequency servo-circuit. Since the magnetic force necessary to support the buoy

at a given position is dependent on the buoyant force, measurement of the solenoid

current needed to support the buoy in the liquid relative to vacuum at the same

position and temperature yields the liquid density directly.

The relation used to compute the density of the liquid with the one solenoid

system is

Pi = ('"b/^^b){i-ai//v)}, (1)

where Pi is the mass density of the liquid, 7}i^^ is the mass of the buoy, V^, is the volume

of the buoy, and /, and are the solenoid currents required to support the buoy at the same position in the liquid and vacuum, respectively.

The procedures used in this study were basically the same as those used in measuring

liquid densities of the pure fiuids.^^'^'^^ Vacuum measurements were made immediately before or after those for nitrogen + methane liquid-mixture points, and

each measurement was made with a separate fill. Since the temperature of the equilibrium cell had to be increased nearly to room temperature for effective removal

of the heavy hydrocarbons, it was necessary to make vacuum measurements before

introducing mixtures containing the heavy hydrocarbons. Measurements for these mixtures generally were made in pairs at 5 K increments with a single fill. With few

exceptions a liquid-methane density measurement was made each day as a control on the measurement parameters. Liquid methane was used as the vapor-bulb fluid to provide the criteria for adjusting the control heat to the top and bottom of the

cell to minimize temperature gradients. The heater currents were adjusted so that the

methane vapor pressure was consistent with the temperature (IPTS-68) determined

with a platinum resistance thermometer mounted near the bottom of the cell. Vapor

bulb and equilibrium cell pressures were measured simultaneously with quartz

Bourdon-tube pressure gages (0 to 0.69 MPa) calibrated against an air dead-v/eight

gage. The estimated maximum uncertainty in calibration of these gages is about

+ 70 Pa. Since the uncertainty in the measured density of a binary liquid mixture is inherently

larger than for the pure fluids due to the added uncertainty in composition, pre- cautions were taken to assure that the uncertainty in composition was minimized and

that the composition in the equilibrium cell was homogeneous.

Basically, there are three options available to fix the composition of a liquid

mixture to be studied experimentally. These are (1) liquid-phase sampling and analysis

relative to calibration mixtures, (2) introducing known quantities of each pure component and mixing within the experimental chamber, and (3) introducing the desired

mixture, prepared under carefully controlled conditions, into the equilibrium chamber

in the mixed state. Each method, or the various combinations, requires an exact accounting of the amount of each component at some point in the process. The

third method was considered to be the most desirable and potentially the most

accurate for this study.

The mixtures were prepared gravimetrically in thoroughly cleaned and dried metal

D-3
876 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

cylinders, each with a free vokime of about 3 dm^ and a tare mass of about 4 kg. In a few cases, cylinders with about 7 dm^ free volume and a tare mass of about

12 kg were used. All gases were research grade, and were analyzed chromatographically before use. In addition, nitrogen and methane were passed through roomtempcralure molecular-sieve adsorption columns to remove moisture and any heavy

contaminants not detected by analysis. The amount of each component added to a

cylinder was determined by difference weighings using a Class S weight set and a

precision equal-arm balance with a capacity of 25 kg. An identical cylinder filled with nitiogen gas at atmospheric pressure was used as ballast on the opposite pan. The standard deviation of 10 repetitive weighings with the balance was determined

by the manufacturer to be 0.51 mg. The standard deviation of 1 1 repetitive weighings

as used in the preparation of mixtures in the laboratory was determined to be 0.67 mg.

Since the uncertainty in the Class S weights is ten times lower than the standard

deviation in the weighings, the uncertainty in the amount of substance of each component ill the mixture prepared is dependent only on the random error in the weighingTABLL 1. Uncertainty 5.v in mole fraction of each component in the prepared mixtures based on

the total amount of substance n prepared

6x

Component n = 1 mol K = 5 mol

N2 ±0.00014 ±0.00003

CH4 ±0.00025 ±0.00005

QHa ±0.00013 ±0.00003

CnHs ±0.00009 ±0.00002

C4H10 ±0.00007 ±0.00001

The estimated error in rnole fraction of each component is given in table 1 for both

1 and 5 mol of mixture prepared. Since two weighings are required to determine the

amount of substance of each component added, the estimated errors arc based on

6 times the standard deviation determined in our laboratory.

The composition, molar mass, and the total amount of substance prepared are given in table 2 for each of the binary mixtures included in this study. A comparison

of the uncertainties in component composition given in t able 1 with the total amount

of substance of mixture prepared, given in table 2, is a direct indication of the uncertainty in composition of each mixture. Three of the mixtures given in table 2

(mixtures with .x ^ 0.5 of methane + ethane, methane + propane, and ethane +

propane) were obtained from the U.S. Bureau of Mines in Amarillo, Texas. The

estimated uncertainties in component composition of these gravimetrically prepared

mixtures are roughly the same as those given in table 1.^^^ A schematic diagram of the apparatus as used to measure liquid mixture densities

is given in figure 1. This arrangement incorporates the same capabilities as the closed

loop vapor-recirculntion apparatus used in liquid-vapor equilibrium measurements^'*' except for vapor sampling. A window in the equilibrium cell allows visual

observation of the liquid sample from about 2 cm above the bottom of the cell cavity

D-4
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 877

TABLE 2. Prepared binary mixtures: M denotes molar mass and the total amount of substance prepared

Mixture Mjg mol "

^ «/mol

0 04752N^ 4- 0 95"'4SrH« 16 61 IQ 6 Ifl 0. JU 0 '!0149N, + 0 6965 1 CH^ 1 9 675Q on

?0 9481 0 O^OI4No — 0 979S6r-,H= tJ .

tjj 1 in

0 01794No 4- 0 96^06roHo &'K 4870 J.1 71/.J 0.06740N2 + O.9326OC3H8 43.0132 1.23

S CM. 0 49'!25rH^ 4- 0 50675roHo " 23.1513 0 68006rHA 4- 0 lI994CoH= 20.5309 4 87

0 295 ^SCH^ 4- 0 7046ToH= JJ.QV 3 5 S 1 06\J\J 1 97 0 496'?7rH. -V- 0 SO^filC-jHo 30.1720 9 10 0 749''0rH^ 4- 0 ^5nsoroH,, 23.0790 1 54 0 85796rHi 4- 0 14''0-ir-,H<. 20.0279 4 79

0 4S687rH^ 4- 0 snnz-c^H,,, 37 6362 1 61 0 5SS7RrHx 4- n 41 1 7'';i-r.H,« 1 09 0 91674rH^ 4- 0 0S^26«-r^H,TM 19.5467 1 85

0.50105C2H6 + 0.49S95C3H837.0689 2.23 U.O/Zo/v^rls ~r U. jL.3rj8 J4.0J00 J.1)4 O.6S939C2H6 4- O.3IO6I/-QH10 38.7840 1.21 O.72436C2H6 4- O.27564/-C4H10 37.S030 1.78 0.65343C2H6 + 0.34657/7-C4H10 39.7929 0.83

0.671 ITCzHs 4- 0.32S83/;-C4Hio 39.2952 0.96 O.4903OC3H8 4- O.5097O/-C4H10 51.2468 0.74 O.50326C3H8 4- 0.49674/-CJI,o 51.0650 0.75 O.58692C3H8 4- 0.4130S/;-C4Hio 49.8915 0.53 O.6O65OC3H8 4- 0.39350/r-C4Hio 49.6169 0.54 O.6O949C3H8 4- 0.3905 l«-C4H,o 49.5749 0.58 0.47039;-C4Hjo + 0.52961«-C4Hio 58.1243 1.03

° Obtained from the U.S. Bureau of Mines, Helium Operations, Amarillo, Texas.

up to the base of the vapor bulb. The vapor bulb, attached directly to the closure

plug, is a slip fit in the top section of the cell. The vapor leaves the top of cell through

a capillary tube passing through the vapor bulb. The density equilibrium system was designed so that the vapor volume, excluding the free volume (65 cm^) in the

recirculation pump, is extremely small relative to the liquid volume. The vapor

volume includes approximately 0.42 cm'^ in the cell, 0.43 cm'' in the access tubing

witliin the cryostat, and 3.3 cm^ in the pressure gage and tubing outside the cryostat.

The volume occupied by the liquid is approximately 20.5 cni'^. The vapor volumes

were calculated from known dimensions, the liquid volume was determined by filling

the cell with water, and the pump voluiue was determined by gas expansion. Without

the pump volume, the elTect of the vapor volumes on composition and density of the

liquid is quite small and becomes important only at the higher mixture vapor pressures

(0.2 to 0.3 MPa).

D-5
878 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

Vac ^tx:—'

Vapor

bulb

Liquid ^1

mixture^"

. I

Recirculation ^)unip

Vent

and

vac

-ix}—

Prepared

gas mixture

Chromatograph

• Cryostat

1 Sample

1 receiver

FIGURE 1. Schematic diagram of experimental apparatus.

The prepared gas mixtures were condensed directly and continuously into the

equihbrium cell through the capillary vapor inlet tube at the bottom of the cell until the last vapor bubble disappeared below the vapor bulb. This filling method

was used to provide continuous mixing of the liquid during the fill, analogous to vapor recirculation. For m.ixtures containing only the heavy hydrocarbons, the vapor

pressures were extremely low, and the amount of vapor space left in the cell was

unimportant. Nevertheless, the cell v/as filled with liquid as discussed above. There

were no visible bubbles when filling with these mixtures.

For methane + heavy hydrocarbon mixtures, comparison of the measured densities before and after vapor recirculation provided a simple test of homogeneity of the

liquid mixture. For these mixtures, the vapor phase is essentially pure methane at the temperatures included in this study. Ethane, the most volatile of the heavy components, has a vapor pressure of only 0.00383 MPa at 140 K.^'^^ Initially, the re- circulation pump was filled with pure methane gas at a pressure equivalent to the

vapor pressure of the mixture for the second experimental temperature, and isolated

from the system. The solenoid currents for a pure liquid methane point and two vacuum points, separated by 5 K, were taken first. The prepared binary gas mixture

to be studied was then condensed into the equilibrium cell in the manner discussed

above. Solenoid ciuixnts for the two liquid-mixture points were measured at temperaD-6
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 879

tures corresponding to those of tlie vacuum points, the lower-temperature point

generally being taken last. Subsequently, the system was opened to the pump, and

vapor was recirculated through the liquid at one to three bubbles per second (probably

less than Icm^min""^) for several minutes. A low recirculation rate was used to avoid entrainment. The pump was then turned oil', and the solenoid current for the

liquid mixture point was remeasured. No change in density could be detected outside

the precision of the measurement for any of the reported binary-mixture points thus

tested. For mixtures containing heavy hydrocarbons only, the most direct means to determine that the liquid sample was homogeneous and of the same composition as the prepared mixture was by liquid sampling and analysis. Ethane -f propane was

selected for this test. Liquid samples were withdrawn under constant helium-gas

pressure (about 0.3 MPa) after the density measurements were completed. During

sample withdrawal, the solenoid current was monitored to detect any variations in density as a different part of the liquid sample surrounded the magnetic buoy. Due

to the extremely low vapor pressures, the compositions of these liquid mixtures are not subject to change by preferential vaporization during sampling. Each liquid

sample was analyzed chromatographically using the prepared gas mixture for cali- bration. For these liquid mixtures, no change in solenoid current could be detected

during sample withdrawal, and the composition of the liquid was found to be consistent with that of the prepared mixture within the precision of the gas analysis,

i.e. within a few hundredths of 1 mole per cent. Liquid samples of methane + ethane and methane + propane were also withdrawn and analyzed subsequent to the density measurements and recirculation of

the vapor. However, it was extremely difficult to obtain samples of consistent composition due to preferential vaporization. At the higher temperatures (^135K)

samples with compositions consistent with the prepared mixtures could be obtained

by using the recirculation-pump volume as pressure ballast during withdrawal. At

lower temperatures it was necessary to pressurize the cell v/ith helium gas to obtain

samples with compositions equivalent to those of the prepared mixtures. In general,

however, analyses of liquid samples of the methane + hydrocarbon mixtures were mainly useful to determine that there were no gross discrepancies (greater than a few tenths of 1 mole per cent) in composition and that the liquid mixtures were not

inadvertently contaminated. No attempt was made to recirculate the vapor or to sample and analyze the liquid mixtures containing nitrogen.

3. Results and discussion

EXPERIMENTAL RESULTS

The experimental orthobaric liquid-jnixture amount-of-substance densities are given

in table 3 as a function of temperature. The excess volumes V^, also given in table 3, were computed from the expression:

V^-Y.x,{V, + li,V,(p,-pJ], (2)

i where V„ is the molar volume, p is the saturation pressure, x is mole fraction, and j5

D-7
880 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

TABLE 3. Orthobaric liquid amount-of-substance densities p of binary mixtures of low molar-mass

alkanes and nitrogen. T, temperature (1PTS-6S); ^caic, P calculated from equation (4); p, pressure; V^, excess volume

Mixture

T

K

P 10^ /^expt Pcalc P

mol dm~^ /'calo MPa cm^ mol~ *

0.04752No + O.95248CH4 105.00 26.8476 -0.006 0.138 -0.144

110.00 26.4052 0.010 0.199 —0.258 115.00 25.9374 -0.002 0.263 —0.442 120.00 25.4522 —0.006 0.350 —0.889

125.00 24.9496 0.005 0.460

130.00 24.4210 0.007 0.583

135.00 23.8600 —0.017 0.730

140.00 23.2809 0.009 0.920 O.30349N2 + 0.69651CH4 100.00 26.8735 -0.010 0.345 -0.584

105.00 26.3393 0.023 0.466 —0.885

110.00 25.7686 —0.005 0.618 — 1.353 115.00 25.1790 —0.017 0.801 —2.253

1 20.00 24.5737 0.010 1.011 —4.510

0.4y24^N2 + O.SU/jtSCHi 95.00 27.0s01 0.006 0.330 —0.541

100.00 26.4588 0.003 0.465 —o.ni

105.00 25.8106 -0.012 0.637 -1.154

110.00 25.1387 -0.016 0.844 -1.803

115.00 24.4431 0.006 1 .097 —3.056 120.00 23.7096 0.017 1.398 —6.110 125.00 22.9315 0.010 1.731 130.00 22.1005 -0.015 2.110 O.O5933N2 -h 0.94067C2Hg 105.00 21.4718 0.385 -0.423

110.00 21.2912 0.463 -0.590

115.00 21.0845 0.547 -0.804

120.00 20.8998 0.638 -1.385

0.02014N2 + 0.97986C3H8 1 10.00 16.2131. 0.357 —0.208

115.00 16.0931 0.471 —0.289

0.03794N2 + 0.96206C3H8 105.00 16.4638 0.495 — 0.310

110.00 16.3410 0.671 —0.392 0.06740N2 + 0.93260C3H8 100.00 16.8055 0.631 —0.427

105.00 16.7084 0.880 —0.628

0.35457CH,i + 0.64543C2H6 105.00 23.1032 0.002 0.0256 -0.382

110.00 22.8777 0.009 0.0392 -0.442

115.00 22.6478 0.007 0.0580 -0.505

120.00 22.4035 -0.050 0.0826 -0.554

125.00 22.1872 0.030 0.115 -0.673

130.00 21.9441 0.002 0.155 -0.798

O.49325CH4 + O.5O675C2H6 105.00 23.9619 0.031 0.0325 -0.525

110.00 23.6937 -0.004 , 0.0503 -0.569

115.00 23.4328 0.003 0.0749 -0.639

120.00 23.1559 -0.047 0.108 -0.697

125.00 22.8933 -0.024 0.150 -0.801

130.00 22.6290 0.007 0.205 -0.927

135.00 22.3581 0.024 0.272 -1.068

140.00 22.0765 0.009 0.355 -1.223

D-8
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 881

TABLE 3

conliniied

Mixture

T

K

P mol din~^

1 0" ^^^^^ Pca.\o MPa

J/E cm^ mol ~

O.6SOO6CH4 + 0.31994C2He 105.00 25.1027 0.002 0.0416 -0.524

110.00 24.7802 -0.004 0.0645 -0.562

115.00 0.003 0.0963 -0.621

120.00 24.1402 -0.001 0.138 -0.698

125.00 23.8212 0.002 0.193 -0.802

130.00 23.5007 —0.001 0.262 —0.933 O.29538CH4 + 0.70462C3Ha 105.00 18.5132 0.0270 -0.469

110.00 18.3624 0.0409 -0.524

0.49637CH4 + O.50363C3H8 105.00 20.4909 0.005 0.0384 —0.727

1 10.00 20.3046 —0.002 0.0591 —0.814

115.00 20.1180 —0.006 0.0874 -0.915

120.00 19.9311 -0.007 0.125 -1.033

125.00 19.7471 0.014 0.173 -1.179

130.00 19.5546 -0.004 0.232 -1.329

O.7492OCH4 + 0.25080CaH8 105.00 23.4768 0.C05 0.0478 — 0.700

1 10.00 23.2064 —0.009 0.0738 —0.783

1 15.00 22.9364 —0.004 0.110 —0.887 120.00 22.6665 0.017 0.158 -1.014

125.00 22.3818 -0.010 0.222 -1.141

130.00 22.1019 0.002 0.303 -1.310

O.85796CH4 + O.I4204C3H8 105.00 24.9622 -0.007 0.0516 -0.553

110.00 24.6331 0.009 0.0801 -0.617

115.00 24.2941 0.006 0.120 -0.684

120.00 23.9491 0.002 0.173 -0.764

125.00 23.5941 -0.021 0.242 -0.855

1 30.00 23.2461 0.012 0.330 —0.992 0.48687CHi + O.51313/-C4H10 110.00 17.3575 0.0629 -0.803

115.00 17.2076 0.0938 -0.884

1 20.00 17.0639 0.1361 -1.002

125.00 16.9156 0.1852 -1.125

0.58828CH4 + O.4II72/J-C4H10 120.00 18.6495 0.1636 — 1.312 125.00 18.4772 0.2281 — 1.466 125.00 18.4853 0.2281 — 1.489 130.00 18.3058 0.3183 -1.646

0.91674CH4 + 0.08326/?-C4Hio 105.00 25.1536 0.009 —0.599

110.00 24.7960 —0.021 —0.638

115.00 24.4512 0.010 —0.719

120.00 24.0910 —0.011 —0.797

125.00 23.7370 0.006 -0.916

130.00 23.3789 0.018 -1.063

135.00 23.0110 0.003 -1.234

140.00 22.6391 -0.015 -1.451

O.5OIO5C2H,3 + O.49895C3H8 105.00 18.3618 0.021 -0.040

110.00 18.2169 0.001 -0.036

115.00 18.0726 -0.012 -0.034

120.00 17.9282 -0.020 -0.033

125.00 17.7880 0.000 -0.047

D-9
882 M. J. HIZA, \V. M. HAYNES, AND W. R. PARRISH

TABLE 3-—continued

Mixture

i P 2Q9. ^expt ~ /'calo P

J/E K mol dm~^ Pcaio MPa cm^mol'

0.501 05C2H6 + O.49895C3H8 130.00 17.6412 -0.011 -0.041

17.49S8 0.009 —0.051

140.00 17.3526 0.013 -0.051

0.67287C2Hg + 0.3271 3C3Ha 125.00 18.6192 —0.044

-0.053

18.3059 -0.052

140.00 18.1509 -0.065

O.68939C2H6 -h 0.31061/-C4Hio 1 15.00 17.3716 -f 0.01

120.00 17.2344 +o!oi5

0.72436CoH6 + O.27564/-C4H10 ins on 171 t .J077Q 1 1 y +0.013

1 1 0.00 17 8401 +0.008

1 7 471'i -0.010

1 in nn 1 7 7S7S -0.013

0.65343C2Ha + O.34657H-C4H10 115.00 17.2184 -0.055

120.00 17.0824 -0.045

0.671 nCoHc + 0.32883«-C4Hio 1 10.00 17.5047 0.003 -0.045

1 1 s nn 1171 .J"KlOft / VJU —0.000 -0.050

1 7s nn 17 1 n'? 1 n nnQ -0.060

130.00 —0.020 -0.042

135.00 16.8285 -0.006 -0.045

140.00 16.6947 0.014 -0.054

O.4903OC3H8 + 0.50970/-C4H,o 105.00 14.3080 -0.002 +0.086

110.00 14.2136 -0.007 +0.078

1 1 s nn 14 I7IQ 0.01

+0.056

1 "^n nn 14 n"'S7 n nni +0.057

125.00 13.9300 -0.002 +0.054

130.00 13.8342 -0.002 +0.052

O.50326C3H8 + 0.49674(-C4Hio i^s nn 1 ? Q71 8 +0.047

130.00 13.8737 +0.054

O.58692C3H8 + 0.41308«-C4Hio 1 in nn i 4,UO J? —0.034

135.00 14.1748 +0.021 140.00 14.0786 +0.006

O.6O65OC3H8 + 0.39350/!-C4Hio 14 1 147 +0.010

Ids fWI 14 nT?"? + 0.015

1 sn no +0.009

O.6O949C3H8 + 0.39051«-C4Hio 115.00 14.6487 -0.017

120.00 14.5521 -0.036

O.47039/-C4H10 + 0.52961/;-C4Hio 125.00 12.6943 +0.016

130.00 12.6133 +0.013

135.00 12.5271 +0.04S

140.00 12.4447 • +0.053

D-10
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 883

is the isothermal compressibility. Subscripts m and i refer to the mixture and to the

pure components, respectively. The pure-component molar volumes were calculated

from the fit of the experimental results/^" Only those for nitrogen, methane, and

ethane were adjusted to the mixture pressure where appropriate. Isothermal compressibilities for nitrogen and methane were taken from Rowlinson^^'^^ and those for ethane were taken from Miller^^^' assuming linear temperature dependence. Excess volumes for a few representative methane -I- ethane points were also computed

using isothermal compressibilities derived from the recent methane data of

Goodwin.^^"^^ The excess volumes using Goodwin's vakies of /? were less than 0.1 per cent different from the excess volumes computed using those of Rowlinson.

Rowlinson's values were used here only because excess volumes for methane and

nitrogen systems reported in the literature are based on his values. Tlius, a direct comparison of excess volumes can be made without assessing the contribution of

different compressibility values. The ethane compressibility values of Miller were

chosen for the same reason. Vapor pressures for nitrogen, methane, and ethane were

taken from Strobridge,^^^^ Goodwin,^ ^''^^ and Goodwin, Rodcr, and Straty,^^*^

respectively.

Effective molar volumes for /z-butane below its triple-point temperature (134.8 K)

were obtained from equation (2) by assuming that the small negative excess volume

of ethane + /z-butane was constant and equal to the average value of the excess volumes above the triple-point temperature of n-butanc. These subcooled liquid

molar volumes were fitted as a linear function of temperature to obtain the equation:

FOi-CJ = 65.63936 4- 0.0992 160(77K). (3)

The molar volumes calculated from this expression at 135 and 140 K agree with the experimental values^^^ v/ithin 0.01 per cent. At 105 K, the molar volume of n-butane

calculated from the equation given in reference 3 fitted to the experimental liquid

densities is 0.056 per cent larger than the value given by equation (3). Equation (3) was used to compute the excess volumes given in table 3 for all of the «-butane

mixtures below 135 K. For /-butane, the liquid-phase equation given in reference 3 was used to obtain subcooled liquid molar volumes below the triple-point temperature

(113.6 K). In examining the excess volumes for propane + o-butane and /-butane + /z-butane

using 7z-butane molar volumes from equation (3), an interesting anomaly was noted.

The excess volumes for these systems, as shown in figure 2, appear to have a dis- continuity at about the triple-point temperature of /j-butane. Molar voluines of

«-butane determined from these systems in the same manner as those determined

from ethane -t- «-butane are in good agreement with each other. However, the

molar volumes calculated from a linear fit of the vakies from propane + //-butane

and /-butane + //-butane are 0. 14 and 0.09 per cent lower than those from equation (3) at 1 10 and 130 K, respectively, and the extrapolated volumes are about 0.075 per cent lower than the experimental liquid molar volumes at 135 and 140 K.

Though the differences noted are not very large, the imprecision of the density

measurements for these heavy hydrocarbons and their mixtures is small enough (see

D-11
884 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

the ethane + Ai-butane and propane + /-butane mixtures in table 3) to suggest that

this behavior is real and would be worth investigating in more detail. This behavior

might also be important in the development of precise methods to predict densities of mixtures containing n-butane.

The pressures listed in table 3 are considered only approximate mixture vapor

pressures, and not all of these were directly measured in the present experiment.

Pressures are given only for mixtures where sufficient measurements were made to allow either interpolation in temperature or composition for a given system or comparison with existing phase equilibria. For nitrogen + methane, several random

pressure measurements were made which were consistent with those interpolated

from previous phase-equilibrium measurements in our laboratory.^^^' As a result,

all of the pressures listed for nitrogen + methane were obtained from graphical

0.10

0.05 o

E

-0.05

i - C4HJ0 + n-C^H I 4' MO

0.04 per cent in V

0.04 per cent

in V„

oI

CjHg + n - C4H10

110 120 130 140 150 160 r/K

FIGURE 2. Excess volumes of propane + n-butane and /-butane -|- n-butane from the present

study. O, O.58692C3H3 4- 0.41308«-C4Hio; 0, O.6O65OC3HS -1- 0.39350«-CiHio; o, 0.60949 C3H8 + 0.39051fi-CiHio; , O.47039/-C4H10 + 0.52961«-C4Hio.

interpolations of the phase-equilibrium measurements. Pressures for nitrogen +

ethane and nitrogen -I- propane were difficult to measure with any consistency since

they are very strong functions of composition. Most of these pressures were estimated

by comparison of the present measurements with the phase-equilibrium data of Lu

and his colleagues.'^'*' ^' For methane -t- ethane, the pressure corresponding to the second point from one filling of the equilibrium cell was generally consistent with

phase-equilibrium data,^^^'^°' while the first point was usually high by a few per

cent. Pressures for these mixtures were smoothed to the pressures of the second point

by comparison with the data of Miller and Stavelcy*^'^' and of Miller, Kidnay, and

Hiza.^^^^ For methane + propane, discrepancies in the pressures between points

taken with the same fill were not as apparent, and the values given in table 3 were

not smoothed. Comparisons between the ratios of measured to Raoult's law pressures from the present study with those from the measurements of Stoeckli and Staveley,^^'^

Cutler and Morrison,*^^'^ and Calado, Garcia, and Staveley^^''^ are shown in figure 3. Pressures given for methane -t- /-butane and methane + w-butane, though no phase

D-12
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 885

0O.7492CH4+ O.25OSC3H

1.1

.5. o

1.0 90 100 110 120 130 140 r/K

FIGURE 3. Comparison of ratios of actual to ideal total vapor pressures for methane + propane

at two compositions. O, present study; g, Stoeckli and Staveley;*^^' A, Cutler and Morrison;"^*

, Calado, Garcia, and Staveley.*^^'

equilibrium measurements are available for comparison, would probably exhibit

departures similar to those shown in figure 3.

ANALYSIS OF ERRORS IN LIQUID-MIXTURE DENSITIES

Where density measurements were made at five or more temperatures, amount-ofsubstance densities p at constant composition were fitted as a function of temperature

to the expression previously used in representing orthobaric amount-of-substatice

densities of the pure components •'^

The least-squares coefficients a and h-^, and the values of the critical temperature

and critical amount-of-substance density for each mixture thus treated are given

in table 4. The fourth coefficient 63 was not statistically significant in the fit of any

of these results. Since experimental critical parameters are rarely available for mixtures

at the desired composition, those used here were obtained from the correlation of

Chueh and Prausnitz.^"*^ The standard deviations from the fit of the experimental

densities to equation (4) are also given in table 4 as a percentage of p. The largest

standard deviation obtained was 0.029 per cent in p for (0.35457CIi4' -1- 0.64543C,H6).

The overall uncertainty in the measured densities of the binary mixtures is slightly

larger than for the pure fluids due to the added uncertainty in composition and is dependent on the type of mixture. Estimated uncertainties in the density measure- ments for three representative mixtures—nitrogen -V methane, methane 4- ethane,

and ethane 4- /z-butane—are given in table 5. The estimated errors due to mixture

preparation were determined from the uncertainty in mole fraction of each component in the mixture for total amount of substance of mixture prepared (tables 1 and 2). The errors due to vapor-volume correction were estimated by assuming a volume uncertainty equivalent to that portion of the vapor volume in the equilibrium

cell at the experimental temperature. The sources of the other systematic errors are

3 (4)

D-13
886 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

TABLE 4. Parameters of equation (4) where Ta and Pa are the critical temperature and critical amount-of-substance density of the mixture. The coefficients a, bi, and />2 were obtained from a

least-squares program in which the experimental mass densities to five digits were converted to amount-of-substance densities within the program; a is the standard deviation

Mixture a 61 62 Pc 10^ X

mol Hm ~ ^

ikl\Jl Villi mnl H m "* lllUl Lllll mo) H m ~ ^ mnl Hm ~

0.04752N2 + 0.95248CH4 16.41033 18.47257 -11.57943 188.04 10.258 0.011 0.30349N2 + 0.6965 ICH4 14.92272 20.19078 -10.85599 173.20 10.747 0.023 O.49242N2 + O.50758CH4 14.54530 20.60585 -10.07112 161.48 11.018 0.014 0.35457CHi + O.64543C2H0 13.02060 6.275239 276.40 8.196 0.029 0.49325CH.1 + O.SOSlSC^He 12.99333 7.219530 262.24 8.762 0.028 O.68OO6CH4 + O.31994C2H6 18.86369 -16.08578 19.91557 239.93 9.482 0.003 0.49637CH4 + 0.50363C3H8 9.168092 7.647523 320.33 7.372 0.009 O.7492OCH4 + O.25O8OC3H8 6.367272 24.40468 -11.53932 271.15 9.163 0.013 0.85796CH4 + O.I4204C3HB 8.371599 23.49229 -10.69945 241.28 9.836 0.016 0.9I674CH4 + 0.08326/j-C4Hio 8.975024 12.09284 238.92 11.044 0.015 O.5OIO5C2H6 + O.49895C3HB 9.598348 5.440200 344.42 6.125 0.015

0.6711 7C2H6 + 0.32883«-C4Hio 8.334169 5.886011 359.88 6.082 0.013 O.4903OC3H8 + O.5097O/-C4H10 7.647038 4.065571 392.63 4.472 0.007

TABLE 5. Estimated uncertainties in density measurements

Source of error 0.49242N2 0.49325CH4 0.671 HCzHe

+O.50758CH4 +O.5O675C2HS +0.32883/2-C4H:

Systematic errors llOK 130 K llOK 130 K llOK 130 K

Mass of float 0.002 0.002 0.002 0.002 0.002 0.002 Volume of float at 300 K 0.020 0.020 0.020 0.020 0.020 0.020 Thermal expansion coefficient of barium ferrite 0.022 0.020 0.022 0.020 0.022 0.020

Position of float 0.012 0.013 0.012 0.012 0.009 0.009

Position of main coil. determined from relative measurements 0.020 0.020 0.020 0.020 0.020 0.020 Temperature uncertainty of 0.030 K 0.016 0.023 0.007 0.007 0.005 0.005 Mixture preparation 0.001 0.002 0.001 0.001 0.002 0.002 Vapor volume correction 0.006 0.020 0.001 0.005 0.000 0.000

Total systematic error

" 0.042 0.048 0.039 0.038 0.037 0.036 Three times standard

deviation " 0.042 0.048 0.081 0.084 0.039 0.039

Total uncertainty " 0.08 0.10 0.12 0.12 0.08 0.08

" The total uncertainty was determined from the square root of the sum of the squares of the systematic errors added to three times the standard deviation from the tit to equation (4).

D-14
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 887

the same as those discussed earlier*^'^' for pure-lluid measurements. Tlie total uncertainty was taken as the square root of the sum of the squares of the systematic

errors plus three times the standard deviation for random error. The standard

deviations are those obtained from the fit of the results to equation (4) taken as a percentage of the mixture amount-of-substance density at the specified temperature.

For the estimate of random errors for pure-fluid measurements given in reference 2, the standard deviation of a single density measurement v/as computed relative to the

density and temperature of methane at 105 K for which repetitive measurements

had been obtained. This method of assessing random error could not be used here. Since the standard deviation for methane obtained from equation (4)^^^ was in good

agreement with that computed from repetitive measurements, standard deviations for

the binary mixtures obtained with equation (4) are considered a reasonable basis for

estimating the random error.

It is probable that the overall uncertainties in the densities for some of the mixtures

investigated in this study arc larger than those shown in table 5. Uncertainties in the

results for nitrogen + ethane and nitrogen + propane could exceed the maximum

total uncertainty shown in table 5 by a few hundredths of a per cent. Because of the dew-point limitations on the pressure of the gas mixtures prepared and the high

liquid-mixture vapor pressures, it was diillcult to maintain adequate driving force

during the fill to provide continuous condensation and mixing. Of these two system.s, results for nitrogen -1- propane are considered the least reliable. Also, during the course of this study, difficulties were encountered in attempting to obtain consistent

results for methane + /-butane where .t(CH4) > 0.9. This difficulty could have been

due to a problem in the filling procedure or to a dew-point related problem in the prepared gas mixture. Though this problem was not encountered in measurements

of the (O.9I674CH4 -r 0.0S326;7-C4Hio) densities, it is quite possible that the overall uncertainties in these results are also larger by a few hundredths of a per cent than

the maximum given in tabic 5. Fitting the results for mixtures to equation (4) does not allow a test of their consistency as a function of composition. Where densities are available for a given binary

system at several temperatures and at three or more compositions, preferably at mole

fractions of approximately 0.3, 0.5, and 0.7, excess volumes can be examined for

consistency using a temperature-dependent Redlich-Kister expansion. In this study,

compositions for methane -I- ethane and methane -I- propane v/ere selected to allow

this treatment. As shown in table 2, each of these systems also includes one mixture

obtained from a laboratory with many years of experience in preparing gravimetric

standards. Excess volumes for these systems were fitted to a Redlich-Kister expansion

of the form :

V^lcm^ mor^ - XiX2[{ao + ^Ji(r/K)-fa2(r/K)2}

+ {bo + b.iTlK) + b,{riKr} (2xi - 1) + {Co + Ci(T/K) + c^iT/Knix, - 1), (5)

where Xj is the mole fraction of methane. The least-squares coefficients <7,-, bi, and c,-, and the standard deviation, in per cent of the average mixture molar volume, for

each system are given in table 6. The C; coefficients were not statistically significant

D-15
888 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

TABLE 6. Parameters of equation (5) for methane + ethane and for methane + propane; Xi is the methane mole fraction and a the standard deviation

methane + ethane methane + propane

-14.22184 -11.96725

fll 0.2649993 0.236748

fla -0.001419196 -0.001429237

bo -18.87392 16.59465

6i 0.3108472 -0.3212125

*2 -0.001349755 0.001398221

Co -52.93613

Ci. 0.9887147

Co. -0.004667488

10V< F-i> 0.030 0.040

for methane + ethane. The excess volumes calculated from equation (5) are compared in figure 4 with the experimental values at 110 K from the present study.

The standard deviation for methane + ethane obtained with equation (5) is in very good agreement with that obtained with equation (4) for the methane + ethane

mixture in table 5. However, the standard deviation for methane + propane obtained

with equation (5) is more than a factor of two higher than that obtained with equation

(4) for any of the individual mixtures in the set. The higher value from equation (5)

is considered to be more indicative of the random error in the results for methane +

propane.

The standard deviation given in table 6 for methane + propane was the highest

value obtained in the analysis. With a total systematic error of about +0.04 per cent added to three times this standard deviation ( + 0.12 per cent), the overall uncertainty

for methane + propane would be approximately +0.16 per cent. With the possible

exceptions noted above {i.e. nitrogen + ethane, nitrogen + propane, and methane +

/i-butane), this is believed to be a suitable estimate of the maximum overall uncertainty

in the densities of binary liquid mixtures obtained in this study.

I \ I I 0 0.2 0.4 0.6 0.8 1 x{CH^)

FIGURE 4. Excess volumes for methane + ethane and methane + propane from the present study at 110 K. O, experimental; , calculated from fit to equation (5).

D-16
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 889

COMPARISONS OF EXCESS VOLUMES

Equation (5) has also been used to compare the present results for methane + ethane

and methane + propane with those of other investigators at 108.15 K, a temperature

approximately common to all of their measurements. The excess volumes were taken

directly from the literature where reported, or otherwise were calculated from the

pure-fluid molar volumes in their data set. Though some of the results were O.I to

0.3 K below 108.15 K, the differences in temperature do not affect the comparisons

of excess voIum.es appreciably. From equation (5), a change in temperature of 0.1 K

results in a change in excess volume of 0.001 cm'' mol~' for methane + ethane and

about 0.002 cm"' moP* for methane + propane.

In figure 5, excess volumes for methane + ethane calculated from equation (5) at 108.15 K are compared with those from the experimental data of Shana'a and

Canficld/"> Rodosevich and Miller/"^ Pan, Mady, and Miller,^"^ Klosek and

McKinlcy,*^^^' and Jensen and Kurata.^^^^ The data from references 26 and 27 are

at about 108 K and those from reference 28 are at about 107.9 K. The excess volumes

from Shana'a and Canfield and from Miller and his colleagues are in excellent agree- ment with the curve calculated from the present results. V/ith the exception of one

point each from Shana'a and Canfield and from jVliller and his colleagues, the

differences are equivalent to much less than 0.1 per cent in the mixture molar volume.

In contrast, the excess volumes from Klosek and McKinley and from Jensen and

Kurata are much less consistent with the present results. The differences from the

calculated curve are equivalent to 0.15 to 0.3 per cent in the mixture molar volume.

In figure 6, excess volumes for methane + propane calculated from equation (5)

D-17
890 M. J. HIZA, W. M. HAYNES. AND W. R. PARRISH

I 1 1 I I 1 0 0.2 0.4 0.6 0.8 1 A(CH,)

FIGURE 6. Comparison of excess volumes for methane + propane at 108.15 K. , Calculated from fit of present results to equation (5); , Shana'a and Canfieid;'^^' A, Rodosevich and Miller;'^®' A, Pan, Mady, and Miller;'"' O, Jensen and Kurata.'"'

at 108.15 K are compared with those from the experimental data of Shana'a and

Canfield/^^' Rodosevich and Miller/^^' Pan, Mady, and Miller,^^^' and Jensen and

Kurata/^^^ For this system the excess volumes from Shana'a and Canfield and from

Miller and his colleagues are also in excellent agreement with the curve from the present results with a maximum difference of about 0.06 per cent in the mixture

molar volume. The excess volume from Jensen and Kurata again is not consistent

with the present results. The difference is about 0.5 per cent in the average mixture

molar volume, in the opposite direction from that found for methane + ethane.

Though there are only a few methane + //-butane points reported in the literature, a comparison can be made at 108.15 K in the methane-rich region between the excess volume interpolated from the present results for the (0.91674CH4 -I- 0.08326rt-C4Hio)

mixture and excess volumes from the experimental data reported by Shana'a and

Canfield^^^^ and by Miller.^^^^ This comparison is given in figure 7. The excess volume

from Shana'a and Canfield was computed using their pure methane data and the

_nfll !

' ' 0.90 0.95 , 1

FIGURE 7. Comparison of excess volumes of methane + n-butane at 108.15 K. O, Interpolated

from the present study; , Shana'a and Canfield;'^^' A, Rodosevich and Miller.'^'^'

D-18
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 891

molar volume of /z-butanc obtained from equation (3). The excess volumes of Miller

are those reported in his paper. The «-butane molar volumes used by Miller are within 0.02 per cent of the values given by equation (3). The difference between the excess volume interpolated from the present results and the curve drawn through the

excess volumes of Shana'a and Canfield and of Miller is about 0.14 per cent of the mixture molar volume. Since the data from Shana'a and Canfield and from Miller

appear to be in as good agreement for methane + n-butane as for methane + ethane

and methane + propane, it is possible that at least part of the 0.14 per cent difference

is due to an unaccounted error in our results for the mixture, as suggested earlier in

this paper. Unfortunately, data are not available for comparison v/ith the present

results for (0.58828CH4 + 0.41172;2-C4Hio), the accuracy of which we have no

reason to question. Measurements for this mixture could not be made at the lower

temperatures since the /^-butane content is the solid solubility limit at about 116 K.^"'*'^

The only data for methane + /-butane in this temperature range are those of

Rodosevich and Miller^^^^ for two mixtures with mole fractions 0.9152 and 0.9462

of CH4. The excess volumes they report for these mixtures at 108 K arc about half- way between their results for methane + propane and for methane + /z-butane at the same metlianc mole fraction. The excess volumes for the mixture of methane +

/-butane with .r ^ 0.5 from the present study are equivalent to those obtained for methane + propane at llOK and the same composition. Excess volumes from the present study are shown in figure 8 for mixtures with x ^ 0.5 of methane + ethane,

-f propane, and + /-butane. Excess volumes are also included for (O.58828CH4 +

0.41 172/2-C4H10) for comparison. It is clear that more extensive measurements of

high precision are needed to describe accurately the composition dependence of the

excess volumes for both methane + butane systems.

The small excess volumes given in table 3 for binary mixtures containing the higher molar-mass alkanes—ethane, propane, /-butane, and /j-butane—show that at

D-19
892 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

cryogenic temperatures the molar volumes for binary mixtures of these components

are closely approximated by the assumption of ideal mixing. The only other investi- gators who report data for binary mixtures of these alkanes at cryogenic temperatures

are Shana'a and Canfield/^^^ They report densities for several mixtures of ethane 4- propane and for one mixture of ethane + «-butane.

For ethane + propane, the excess volume reported by Shana'a and Canfield at 108.15 K for the mixture (O.SSSZCjHg + O.4148C3H8) is compared in figure 9 with

those determined from the present results at two similar compositions. If the excess volumes for ethane + propane exhibit an asymmetry similar to those for methane +

ethane (figure 5), the excess volumes for the two ethane -I- propane mixtures from

the present study should be nearly the same, with the excess volume at the higher

mole fraction of C2H6 slightly larger. Shana'a and Canfield report a maximum

J 0.1 per cent in _0 5U I I I I 1 1 1 105 110 115 120 125 130 135 T/K

FIGURE 9. Comparison of excess volumes for ethane + propane. O, o. Present study at xiCzUe) = 0.50105 and 0.67287, respectively; , Shana'a and Canficld<-=' at .x(C2H6) = 0.5852.

excess volume for this system of —0.485 cm' moP ^ for a mixture containing

(O.7036C2H6 + O.2964C3H8). The difference in excess volumes from the two sets of

measurements is surprisingly large, equivalent to approximately 0.8 per cent in the mixture molar volume. Since the pure-fluid molar volumes for ethane and propane

from Shana'a and Canfield are only higher than those determined with the present

apparatus^'^ by approximately 0.06 and 0.12 per cent, respectively, it is logical to suspect composition error or incomplete mixing as the source of this disagreement.

To assess the effect of composition uncertainty on the excess volume, it was assumed

that the mixture mass density from the present study was exact and that the actual mole fraction of propane was 0.01 larger than the composition of the prepared

mixture with x = 0.5. This results in an error of —0.062 cm'' mol~^ in the excess volume. If the excess volume reported by Shana'a and Canfield were assumed to be

correct, it would be necessary for the actual mole fraction of ethane in the liquid in the present study to be larger by 0.064 than that of the prepared mixture.

D-20
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 893

As discussed in the experimental section of this paper, chromatographic comparisons of the compositions of liquid samples for ethane + propane were in agree- ment with the composition of the prepared mixture within a few hundredths of 1 mole

per cent. The fact that no change in density of the mixture could be detected during

sample withdrawal is considered evidence that the liquid mixture was homogeneous.

The fact that the two mixtures studied were prepared independently in two separate

laboratories is also confirmation that there was no significant error in the mixture

preparation.

Recent enthalpy of mixing measurements in binary mixtures of methane, ethane,

and propane reported by Miller and Staveley'''''^ should also be referred to in regard

to the ethane + propane results discussed above. These investigators report that the

enthalpy of mixing at 112 K is about 129 JmoP^ for methane + propane with

X = 0.5, about 69 Jrnol"^ for methane + ethane with x ~ 0.5, and probably less than 5 Jmol"^ for ethane + propane throughout the composition range. A comparison of ratios of the enthalpies of mixing with ratios of the excess volumes for these systems also tends to support the more ideal excess volumes obtained in the present

investigation.

Shana'a and Canfield include a discussion on the invalidity of the principle of

congruence based on a comparison of their excess volumes for ethane -\- propane

and methane + ethane with those for methane + propane as a function of the

equivalent carbon number. When the excess volumes from the present study are

used, methane + ethane shows the same departure as expected, but ethane + propane

is in excellent agreement with m.ethane + propane. For a detailed discussion of the

method, the reader is referred to Shana'a and Canfield's paper.

In figure 10, the excess volume computed from the molar volume of the (0.8833C2Hg

+ O.II67/2-C4H10) mixture reported by Shana'a and Canfield is compared v/ith the

excess volumes of this system computed from our results. The excess volume of

Shana'a and Canfield was computed using their density for pure ethane and the molar

0 I

1 1 1 1 1 1 '

-V- -0.1 -

FIGURE 10. Comparison of excess volumes for ethane -f- 7!-butane. O, o. Present study at A'CCaHs) = 0.67117 and 0.65343, respectively; , Shana'a and Canfield'^"^' at aCCzHb) = 0.8833.

61

D-21
894 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

volume of «-butane from equation (3). For this system the difference in excess volumes

is equivalent to about 0.25 per cent in the mixture molar volume. Since the molar

volumes for n-butane in the subcooled liquid region given by equation (3) were

obtained from the results for this system the lack of temperature dependence is an

artificial constraint. For this system, if the actual mole fraction of n-butane in the

liquid mixture at 1 10 K was 0.01 larger than the composition of the mixtures prepared

for this study, an error of —0.119 cm' mol"^ in the excess volume would result.

-1

-2

-3

w 111 1 1 1 1 I I

K

-

1 1

\ll5 K

1 1 1 0.1 0.2 0.3 0.4 0.5

FIGURE 11. Comparison of excess volumes for nitrogen + methane. O, Present study; , Rodosevich and Miller;^^''' A, Liu and Miller;'^" V, Massengill and Miller.'^^>

Of the data available for liquid mixtures of nitrogen + methane, the excess volumes reported by Rodosevich and Miller,^^^^ Liu and Miller,^''*' and Massengill

and Miller^'^^ were selected for comparison with excess volumes from the present

results. These comparisons are shown in figure 11. The excess volumes of Massengill

and Miller are from the data of Liu and Miller adjusted with additional nitrogen

measurements. All of the excess volumes of Miller and his colleagues appear to be

in agreement with excess volumes from the present results within 0.1 per cent of the

mixture molar volumes. The height of the symbols is equivalent to about 0.1 per cent of the mixture molar volumes.

The fact that the nitrogen + methane excess volumes are in good agreement does

not mean that the mixture molar volumes are in agreement. It is worth noting that the data reported by Liu and Miller and by Massengill and Miller were obtained with

D-22
LIQUID DENSITIES FOR BINARY MIXTURES OF LNG COMPONENTS 895

a calibration based on the molar volumes of saturated liquid argon reported by

Terry et alP'^^ while all of the other data of Miller and his colleagues^^^'^^'^ ''^ referred

to here were obtained with a calibration based on Jiiolar volumes of saturated liquid

methane taken from Goodwin and Prydz/^*^ From the discussion given earlicr/'^^ the nitrogen -!- methane molar voUimes of Rodoscvich and Miller should be higher

but consistent v.'ith the present results within about 0.1 per cent, while those of Liu

and Miller and of Massengill and Miller should be higher than the present results by about 0.4 per cent.

4. Simimary

The measurements of the present study provide a set of orthobaric liquid densities for binary mixtures of the major components of LNG which arc generally consistent

with those for the pure components within the precision of the measurements. The

maximum random error in tlie densities of the binary mixtures is believed to be about

+ 0.12 per cent, roughly twice that for the pure fluid densities. The known systematic

errors in the densities for both the pure fluids and the binary mixtures were estimated

to be from 0.03 to 0.05 per cent. As noted, the uncertainties in the densities for

methane + //-butane with .x(CH4) > 0.9, and for nitrogen + ethane and nitrogen +

propane, could exceed these estimates.

The largest excess volume found was —6.11 cm^ moP^ for nitrogen + methane

with X = 0.5 at 120 K. This is equivalent to 13 per cent of the ideal mixture molar

volume. In contrast, the present results show that molar volumes of mixtures of the

alkanes, excluding methane, are closely approximated by ideal mixing in the

temperature range studied. The most significant disagreement between the present

results and published data is the 0.8 per cent difference in density for ethane +

propane from that of Shana'a and Canfield.

Based on the excess volumes of the alkane mixtures, excluding methane, from the

present study, it was shown also that elfective molar volumes of subcooled n-butane

in a binary liquid mixture may difier by a small but significant amount dependent on the other components present. It is suggested that this behavior v/ould be worth

investigating in more detail for /z-butane and other fluids such as n-pentane. There is also a definite need for additional measurements on the binary mixtures containing

both //-butane and /-butane with methane.

In subsequent papers, the results of measurements of orthobaric liquid densities of multicomponent mixtures and the ability of theoretical models to predict the measured densities will be reported.

The authors acknowledge the contributions of M. J. Brown, R. C. Miller, and R. D.

McCarty to the correlation of the results.

REFERENCES

1. Robinson, R. L., Jr.; Hiza, M. J. In Advances in Cryogenic Engineering, Vol. 20. Timmerhaus,

K. D.: editor. Plenum Press: New York. 1975. p. 218.

2. Haynes, W. M.; Hiza, M. J.; Frederick, N. V. Rev. Sci. lustrum. 1976, 47, 1237.

3. Haynes, W. M.; Hiza, M. J. J. Chein. Thermodynamics 1977, 9, 179.

D-23
896 M. J. HIZA, W. M. HAYNES, AND W. R. PARRISH

4. Yu, P.; Elshayal, I. M.; Lu, B. C.-Y. Can. J. Chein. Eng. 1969, 47, 495.

5. Poon, D. P. L.; Lu, B. C.-Y- In Advances in Cryogenic Engineering, Vol. 19. Timmerhaus, K. D.:

editor. Plenum Press: New York. 1974, p. 292.

6. Hiza, M. J. ; Kidnay, A. J. ; Miller, R. C. Equilibrium Properties ofFluid Mixtures, A Bibliography

of Data on Fluids of Cryogenic Interest. NSRDS Bibliographic Scries. IFI Plenum: New York.

1975.

7. Hayncs, VV. M. Rev. Sci. Insirum. 1977, 48, 39.

8. Tuliy, P. C. ; Emerson, D. Personal communications. November 1974, August 1976.

9. Duncan, A. G., Hiza, M. J. In Advances in Cryogenic Engineering Vol. 15. Timmerhaus, K. D.:

editor. Plenum Press: New York. 1970. p. 42.

10. Hiza, M. J.; Duncan, A. G. Rev. Sci. Instrum. 1969, 40, 513.

11. Goodwin, R. D.; Roder, H. M.; Straty, G. C. Nat. Bur. Stand. U.S., Tech. Note 684, 1976.

12. Rowlinson, J. S. Liquids and Liquid Mixtures. 2nd Ed. Butterworths: London. 1969.

13. Miller, R. C. Chcm. Eng. 1974, 81, 134.

14. Goodwin, R. D. Nat. Bur. Siand. U.S., Tech. Note 653, 1974.

15. Strobridge, T. R. Nat. Bur. Stand. U.S., Tech. Note 129, 1962.

16. Parrish, \V. R.; Hiza, M. J. In Advances in Cryogenic Engineering Vol. 19. Timmerhaus, K. D.:

editor. Plenum Press: New York. 1974, p. 300.

17. Kidnay, A. J.; Miller, R. C; Parrish, W. R.; Hiza, M. J. Cryogenics 1975, 15, 531.

18. Miller, R. C; Staveley, L. A. K. In Advances in Cryogenic Engingeering, Vol. 21. Timmerhaus, K. D. and Weitzel, D. H.: editors. Plenum Press: New York. 1976, p. 493.

19. Miller, R. C; Kidnay, A. J.; Hiza, M. J. /. Ciieni. Thermodynamics 1917, 9, 167. 20. Wichtcrle, I.; Kobayashi, R. /. Chem. Eng. Data 1972, 17, 9. 21. Stocckli, H. P.; Staveley, L. A. K. Helv. Chim. Acta 1970, 53, 1961.

22. Cutler, A. J. B.; Morrison, J. A. Trans. Faraday Soc. 1965, 61, 429.

23. Calado, J. C. G.; Garcia, G.; Staveley, L. A. K. /. Chem. Soc, Faraday Trans. I, 1974, 70, 1445.

24. Chueh, P. L.; Prausnitz, J. M. AIChEJ. 1967, 13, 1107.

25. Shana'a, M. Y.; Canfield, F. B. Trans. Faraday Soc. 1968, 64, 2281.

26. Rodoscvich, J. B.; Miller, R. C. AIChEJ. 1973, 19, 729.

27. Pan, W. P.; Mady, M. H.; Miller, R. C. AIChEJ. 1975, 21, 283.

28. Klosek, J.; McKioley, C. In Proceedings of the First International Conference on LNG.

White, J. W. and Neumann, A. E. S.: editors. Institute of Gas Teclmology, Chicago, Illinois. 1968. Paper No. 22. 29. Jensen, R. H.; Kurata, F. /. Petrol. Technol. 1969, 21, 683.

30. Kuebler, G. P.; McKinley, C. In Advances in Cryogenic Engineering Vol. 21. Timmerhaus, K. D.;

Weitzel, D. H.: editors. Plenum Press: New York. 1976, p. 509.

31. Liu, Y.-P.; Miller, R. C.J. Chcm. Thermodynamics 1972, 4, 85.

32. Massengill, D. R.; Miller, R. C. /. Chem. Thermodynamics 1973, 5, 207.

33. Terry, M. J.; Lynch, J. F.; Bunclark, M.; Mansell, K. R.; Staveley, L. A. K./. Chem. Thermodynamics 1969, 1, 413.

34. Goodwin, R. D.; Prydz, R. /. Res. Nat. Bur. Stand. U.S. 1972, 76A, 81.

D-24
i '<ia>' w u it w ^

R-1102

Heating value can be well defined in

LNG transfer

VV. R. Parrish, J. M. Arvidson and J. F. LaBrecque,

National Bureau of Standards, Boulder, Colo. LNG SAMPLES may be obtained and anal>-zed from

flowing streams with a precision of ±0.20% in the computed heating value. This value is derived from laborator>' and field tests and is based on three standard deviations, including ±0.06% random error for gas analysis. The

accuracy of the measurement depends only on the accuracy of the gas analysis; all tests show that a properly

designed and operated sampling system produces no detectable systematic ofTsets in the computed heating values. Since LNG is bought and sold on a heating value basis, accurate and precise LNG composition measurement is a

necessity. At current prices, a composition uncertainty

corresponding to a one percent error in the computed

heating value means an inequity of nearly $65,000 for one 125,000 m° shipment.

Sampling LNG presents special problems because the component normal boiling points are so different

methane, the major component, has a boiling point of — 161°C; while n-butane, the minor component, has a boihng point of —0.4° C. Accurate LNG composition measurement requires a sys- tem containing

• A sampling probe which transfers a representative sample into the sampling system • A sample conditioner which completely vaporizes the sample • A gas analyzer which accurately and precisely analyzes the sample.

Finally, all operating variables must be carefully selected

to insure that all system components perform properly. Sampling systems fall into two broad categories—continuous and batch. Trego^ describes a continuous LNG

sampling system which is in operation at the LNG Terminal in Barcelona, Spain. He states that deviation between

hquid samples taken upstream of a vaporizer and gas samples taken downstream of the vaporizer agree to within the error of the gas analysis (~ 0.5 to 0.9%).

Cook' describes a batch sampling system; he reports^ that the device gives good results for sampling LNG

containing 95 mol % or more methane. However, the

precision and accuracy have never been established quantitatively.

This paper describes a system for continuously sampling flowing LNG streams with a total uncertainty of ± 0.20% in the computed heating value. The system can

be used in any LNG line where the pressure is at least 5 psi (32 kPa) above ambient conditions. The system

design, dimensions and recommended ranges of operating

variables aie derived from a systematic study employing

both laborator)' and field tests. The laboratory work

permitted rapid data accumulation under well controlled operating conditions using LNG-like mixtures of known

composition. These tests considered 3 probes, 2 vaporizer

designs and 10 operating variables. Sufl5cient data were

taken to statistically establish the effect of each variable on the sampling precision and accuracy. Using the lab- oratory test results, a full scale sampling system was designed, built and tested aboard an LNG tanker and in the NBS flow facility.* Details and results of this work

are presented elsewhere.'

SYSTEM DESCRIPTION

Fig. 1 shows a schematic of the full scale sampling

system. All field tests were made with the sampling sys- tem having the dimensions given in Table 1. At this time it is not clear which of the dimensions are critical to the sampling system precision. The sample is taken from the LNG line (in our tests a 3 in. (76 mm) pipe and flows through a side tap probe,

past a stainless steel bellows block valve (Tl) and through

a 60 micron filter. A nitrogen purge line is attached to the system to inert the sampling system prior to startup and to back purge the filter if necessary. The LNG then

flows through a stainless steel bellows needle valve (T2),

which controls the sampling rate, and into the steam

heated vaporizer. The vaporizer contains a coiled sec- tion of thin-walled stainless steel tubing and an im- pingement chamber. The impingement chamber causes a

TABLE 1 —Dimensions of LNG sampling system

(See Fig. 1 for system schematic)

Component

Line between test section &

valve. Tl

Line between valve, Tl, and filter (contained a short radius 90-degree bend)

Line between filter and valve, T2

Line between valve, T2, and union

at vaporizer Vaporizer

Vaporizer steam casing (with flat welded ends) Impingement chamber (with flat welded ends) Accumulator

Length,

inches (mm)

4.5 (114)

11 (279) 2 ( 51)

13.5 (343) 36 (914)

10 (254)

1.5 ( 38) 16 (406)

Outer

Diameter,

inches (mm)

0.540 ( 13.7 ) ('/. in. Sch

80 pipe)

0.25

0.25

0.25

0.13

6.4 ) 6.4 )

6.4 ) 3.18)

6 (152 )

1,5 ( 38 ) 5.125 (130.2 )

In nor Diameter.

Inches (mm)

0.302 ( 7.67)

0.180 ( 4.57) 0.180 ( 4.57)

0.180 ( 4.57) O.IOI ( 2.56)

5.5 (140 )

1.376 ( 34.95) 4.805 (122 )

114 E-1 April 1978 Hydrocarbon Processing

Vol 57, NO. 4
sudden change in the flow direction and speed to en- hance vaporization of any entrained droplets. All of

the cold lines, the steam lines and the vaporizer are in- sulated with fiberglass pipe insulation which is sealed with duct tape. After leaving the vaporizer, the sample

goes to an accumulator. The accumulator acts as a time- averaging, or mixing, device to eliminate inhomogeneities caused by fractionation during vaporization. The homogeneous gas sample leaves the accumulator, passes through

a manifold containing sample cylinders, a rotameter and

a back pressure regulator before going to the vent system. The sampling rate is set by adjusting the needle valve (T2) and the back pressure regulator. The back pressure regulator is extremely useful because it maintains a constant pressure in the sample cylinders.

TEST RESULTS

Fig. 2 shows the computed heating values for one

series of tests made aboard the LNG tanker El Paso

Consolidated. In these tests liquid samples were taken upstream of the shipboard steam vaporizer. Analyses of these samples were compared with those of gas samples

taken from the completely vaporized stream. A laboratory gas chromatograph was used to determine the sample composition. The average heating value of the gas samples was 0.04% higher than that of the liquid samples.

Also, the estimated standard deviation for both sets of samples was 0.04%. This precision is comparable to the estimated standard deviation of 0.05% in the heating value for gas analysis alone. A statistical analysis of computed liquid densities gave an estimated standard deviation of 0.02% for both the liquid and gas samples. This

test shows that, within the precision of the gas analysis, samples taken from the liquid stream are indistinguishable from the samples taken from the totally vaporized

gas stream. Table 2 lists the variables evaluated in the laboratory

and field sampling tests and groups them according to their efTect on sampling precision and accuracy. Each

variable's effect on sampling precision was measured by

repeated sampling under controlled conditions. The ac- curacy was determined in the laboratory tests by sampling

mixtures of known composition. The only verification of accuracy in the field tests was made by comparing the

liquid sample compositions with samples taken from the

totally vaporized LNG stream. The test results indicated

that for uninsulated liquid lines the heat leak causes backflashing of nitrogen (and probably methane) which enriches the samples in the heavy (Ca*) components. However, insulating the line with a J/j to 1 inch (12 to 25 mm) thick layer of fiberglass sealed with duct tape is adequate to eliminate the heat leak problem. No other

variable tested afTected sampling accuracy. Therefore, by

using insulated lines, the accuracy of the composition measurement depends only on the accuracy of the gas

analysis. Five variables were found to adversely afTect sampling precision. Both laboratory and field tests showed

that below a certain sampling rate, the sampling precision diminishes; this minimum sampling rate varied between various sampling systems. A mechanism for the sampling rate's importance is unknown. For the sampling

system described here, the sampling rate should be greater than 20 standard liters per minute of gas. Laboratory results clearly indicated that a small di- ameter tube vaporizer was better than a vaporizer with a large cross sectional area and that rapid sample vaporization gave the best results. However, there is no advantage

in having the vaporizer outlet temperature above 100° F

Fig. 1—LNG sampling system.

Hydrocarbon Processing April 1978 E-2

115
LNG SAMPLING

1167.0 -

° 1166.5

c 1166.0-

2 1165.5

1165. (Jl 43.40

4 6 8 10 12 Time, h Rg. 2—Computed real gas healing values of shipboard data.

TABLE 2—Variables evaluated for their effect on LNG sampling precision and accuracy

Variable effecting both sampling precision and accuracy:

Heat \tik to liquid sample line

Variables afletting sampling preciswn but not accuracir: Sampling rate Vaporiier design Time averaging the vaporized sample

Sampling rate transients Probe

Variables not affecting sampling precision and accuracy; Temperature and pressure at the sampling point Pressure differentral between the sampling point pressure and the equilibrium LNG pressure Flow rate past the sampling point Pressure drop tn the liquid sample Irne between the sampling point and vaporizer Composition of the liquid being sampled

About the outhors W. R. Pajwish conducts basic and applied experimental and theoretical re- search involving cryogenic systems for

the National Bureau of Standards. He

is a PhD. graduate in chemical engi- neering from the University of California, Berkeley. Dr. Parrish also has done

post-doctoral work at University of Wisconsm, Madison. He is a member of AICKE.

3. M. Arvtdson holds the B. S. degree in mechanical engineering from the Unu

versity of Colorado. He is experienced

in research in LNG metrology, mechanical properties of solids at low tempera/- turee and pressure measurement studies at low temperatures. He is currently engaged in basic and applied experi- mental research in cryogenic systems. Mr. Arvidson is a member of Sigma Xi

and the Instrument Society of America.

(38° C). Both steam and electrically heated vaporizers

produce comparable results. An impingement chamber

is unnecessary when using an electrically heated vaporizer. This is because the electrically heated unit vaporizes

the sample under constant heat flux conditions. The

steam vaporizer transfers heat with a constant wall temperature. This is less effective due to the film boiling. The need to time-average the vaporized sample in an

accumulator arises from fractionation during vaporization. The minimum residence time necessary to obtain

precise results depended upon the sampling system;

residence times of 45 to 120 seconds gave good results. Field tests indicated that taking samples within 30

minutes of a major change in sampling rate diminishes sampling precision. Howe\'er, minor fluctuations and slow

drifts in sampling rates did not affect the results. The side tap probe was found to be more reliable than an upstream facing pitot tube. For unknown reasons, the pitot tube occasionally gave erratic results. The conclusions that certain variables did not affect sampling precision must be considered valid only over

the ranges tested; however, this range usually included

the typical operating ranges encountered during custody

transfer. There is no reason to expect the temperature and pres- sure to affect sampling precision provided the conditions

are far from the critical point of the LNG.

At some low value the difference between the pressure

of the sampled liquid and the saturation pressure of the LNG (i.e., subcooling) in combination with heat leak

will adversely affect sampling precision; however, this effect was not found at a pressure differential of 3.9 psi (25 kPa) (this corresponds to ~ 0.5 K subcooling).

LNG flow rates corresponding to Reynolds numbers

ranging between 1,500 and 50,000 did not affect sampling

precision; it is unlikely that there would be any adverse

effect on precision at higher Re)Tiolds numbers. The fact that a large pressure drop in the liquid

sample line is unnecessar)' eliminates the need for a liquid flow control valve. This conclusion is known to be valid only when using tube vaporizers. However, the needle

valve is useful in setting sampling rates. Finally, there is no problem in sampling LNG mixtures which contain up to 0.15 percent Ce*. The heavy

components would cause problems if they raised the sample dewpoint temperature to near ambient temperature. Additional work is underway to develop an improved

vaporizer design which, hopefully, will eliminate the need for an accumulator. .\lso, additional tests are being

made to determine the criterion for the minimum acceptable sampling rate. The goal is to pro\nde general design and operating criteria for LNG sampling systems.

J. F. LaBrecque is a consultant to scientists arid engineers on the use of statistics in the design and analysis of ex- periments at the National Bureau of Standards, Boulder, Colo. Dr. LaBrecque

is a graduate of the University of Massachusetts (B.S.) and the State University of New York at Buffalo (Ph.D.). He is a member of the American Statistical Association.

ACKNOWLEDGMENT

Work on sampliDR was supported by EI Paso Marine Co., Columbia LNG

Corp., Consolidatcti System LNG Co. and Southern Energy Co. Current

stTiojes on vaporizer desien are supported by the Pipeline Research Committee of the American Gas Association, Iqc.

i LITERATURE CITED

* Trego, J., "System samples LNG accurately," Hydrocarbon Processing,

p. 83. April 1976.

' Cook. H. L. , "Method and apparatus for sampling refrigerated volatile liquids," U. S. Patent No. 3,487,692, January 1970.

* Cook, H. L., Transco Co., Houston, private communication, May 1977.

* Mann, D. B. "Cryogenic flowmetering research at NBS," Cryogenic, Vol.

I'l. p. 179, 1971. Pamsh, W. R. Arvidson, J. M., and LaBrecque, J. F., "Development and

evaluation of an LNG Sampling Meaftirement System, ' ' NBSIK (to be

published).

116 E-3

April 1978 Hydrocarbon Processing

TEST OF DENSniETERS FOR USE IN THE CUSTODY TMNSFER OF LNG

J. D. Siegwarth, J. F. LaBrecque ar.i B. A. Younglove

tJational Bureau of Standards Boulder, Colorado SC;32

INTRODUCTION

The amount of liquefied natural gas (LNG) changing ownership, i.e., custody transfer, may be determined from the total volume of the liquid transferred and the density of the liquid. The density can be calculated from the temperature

and composition or measured directly with a densimeter. Direct density measurements have the advantages that composition measurements are avoided

and the density can be monitored continuously.

Some commercial densimeters have been adapted for

low temperature use. Before these densimeters are

used in custody transfer measurements, it is necessary to establish whether their performance is adequate. Furthermore, methods must be developed

to check accuracy and maintain performance in field

use.

In order to assess the performance of densimeters for LNG custody transfer use, a density

reference system (DRS) has been constructed at the Cryogenics Division facilities of the National

Bureau of Standards.' Four commercial densimeters

have been tested^ to determine accuracy, precision

and short-term reliability. The four densimeters

include two vibrating-element types, one dielectric or capacitance type, and one Archimedes or displacement type. This program, sponsored at flBS by the American Gas Association, Inc., was con- ducted over a period of four years and considers densimeters that were corimercially available at

the start of the work.

THE DENSITY REFERENCE SYSTEM DESCRIPTION

The density reference system, shown schematically in Figure 1, consists of a vacuum-insulated,

liquid-gas sample container of sufficient size and with sufficient access so that a number of com- mercial densimeters and a calibration densimeter

can be installed at the same time. The cali- bration densimeter, built at NSS Boulder, is an Archimedes-type densimeter using a pure silicon

single crystal for the displacement body. The

density of silicon is relatively low and the density of pure single crystals of silicon is accurately known. ^ The silicon crystal is sus- pended on a wire from the pan arm of an electronic

balance and is imjnersed in the fluid in question.

In order to weigh the 127 g silicon crystal on the

0 to 20 g range (which can be read to 1 mg) a counter-balance is placed on the opposite arm. To eliminate the need to determine the mass of this counter weight, the silicon is weighed in the ' fluid, then disconnected. Then a reference mass, chosen so that it weighs on scale, is weighed. The equation for the fluid density contains only

the mass of the silicon crystal, the density corrected for thermal contraction, the mass of the

*This work was carried out at the National Bureau

of standards under the sponsorship of the American

Gas Association, Inc.

385

reference weight, the electronic balance readings when the silicon crystal was weighed in the fluid,

the balance reading with only the reference weight,

and a snail correction for the buoyancy effects on the reference mass from the gas in the balance

space.

All four of the densimeters tested and the reference densimeter were installed and evaluated

at the sa-ie time. Making the density tests simul- taneOLsly necessitated a large sample container.

Not orly does this method save time but it allows

a cross-check between the densimeters. If one densireter should give an erroneous density reading, the instrument at fault can be readily deter- mined when the remainder show agreement.

The sample container, containing the test densireters and the room-temperature electronic

balance space, is connected in common through the tube containing the crystal suspension wire. Both containers are gas tight so the vapor pressure of

the Sc-iple can be varied between 0 and 7 bars allowing a range of densities to be obtained with

one fljid sample.

Tne sample holder and shield are cooled by

flowing cold nitrogen gas or liquid through a coiled tube attached to the outside of the sample

holder. These coils are used to cool the sample,

and resistance heaters are used to heat it when

changing temperatures between measurements . Each

measurerient is made with the sample and container

as nea'ly as possible at isothermal conditions. During the period of time data are being recorded,

the he:t capacity of the sample fluid is used to keep t'.e temperature nearly constant. The heat leak to the sample has been minimized by sur- roundirg the sample container with a thermal shield. The shield temperature is maintained near

that of the sample by controlling the flow of the nitrogen gas through the shield cooling coil. To obtain uniform temperature and density rapidly in the 14-liter vessel, a 5-cm diameter turbine pump

is usei to mix the sample. Liquid is circulated

from t^.e bottom to the top of the sample holder through 3. 5-cm diameter tubes. The circulation

rate is variable and is reduced during actual density measurements so that the densimeters are

not disturbed. Temperature is measured near the bottom and at the top of the sample holder. The temperature differences, AT, from top to bottom of

the sa-ple holder were typically less than 0.1 K.

DENSITY REFERENCE SYSTEM ACCURACY

The random error associated with density measurements made using the DRS was obtained from least squares fits of the measured densities to a power series in temperature (T). A different fit

was used for each of the various compositions.

The estimated standard deviation for measurements

made on the DRS is 0.065 kg/m'. This is a stan- dard de.ietion of less than 0.016S at the normal F-1
CRYOGENIC FLUIDS DENSITY REFERENCE SYSTEM

J [^l Reference Weighf

Vopor Pressure Thermometers

Figure 1

Automatic Balance

, tjr Vent

Silicon Crystal

Sample

Sample Holder

-^Test Densimeters

Radiation Shield

boiling point of methane (422.63 kg/m^). The systematic error due to uncertainties in mass and temperature nieasureaents is estimated to be 0.028", while the uncertainty of a single density measure- ment by the DRS densimeter is estimated to be 0.076%. This is the sum of the systematic error

and three times the estimated standard deviation.

Pure methane density measurements by the DRS densimeter agree with the densities calculated by Goodwin^ to better than 0.03% over the temperature

range from 110 to 125 K. The agreement betv;een the methane densities determined by the ORS den- simeter and those determined by Haynes-Hiza^ is shov/n in Figure 2. The densities are compared

through temperature measurements. The density difference in percent is stiov;n as a function of

the order of data acquisition. There is no evi- dence of a f i 1 1 ing- to-f i 11 ing shift in the density

meesureiTients , even though the DRS was brought to room temperature after each filling. The bias between the mean densities measured by the DRS densimeter and the Haynes-Hi za densities are less thao O.Oln. The DRS is discussed in greater

detail in Reference 1.

DESCRIPTION OF THE DENSIMETERS TESTED

Both vibrating-elcment densimeters determine

fluid density by measuring a resonant frequency of

a mechanically-vibrating element immersed in the fluid in question. Frequency is related to den- sity as fol lows

A + B/f' (1)

where f is the resonant frequency and A and B are constants. Since neither of these instruments had

d suitable calibration for lov/-temperature low- density liquids, the resonant frequency rather

than the density indication, was recorded using a frequency counter. The densimeters v/ere cali- brated using the density data fron: the DRS

densimeter and the corresponding frequencies to determine the constants A and B of Eq. (1). This equation was then used to study the precision,

filling-to-filling offset and composition depen- dencies .

The capacitance densimeter actually measures

the dielectric constant of the fluid in question.

The dielectric constant is combined with a tem- perature measurement to give a density value. The calibration supplied with the instrument was used

in the analysis of the density data.

The displacement densimeter determines den- sity by measuring the buoyant force on a hollow

float. The position of the float is sensed and

the position is maintained by the interaction of

the current in a coil on the float with the field

of a permanent magnet. This current, and the temperature which is used to compensate for tem- perature dependence in the magnet, are combined to give a density. This instrument was factory

calibrated. The factory calibration was used in the analysis of the density data.

DENSIMETER PERFORM/vNCE

Results of the density comparison measurements are shown in Figures 3 through 10. Five of

the six fillings were pure methane and the sixth

was an LNG-like mixture containing about 88-1/2"

CH,, 6-1/2% CjHe, 3% C-^Hg and 2Z nC^H^^. Nitrogen was eventually added to two of the methane

fillings and to the mixture filling as shown in table I.

The data presented in Figures 3 through 10 for the various densimeters is the percent dif- ference between the density indicated by the densimeter under test and that measured by the DRS densimeter. The temperature range of the measurements was 108 to 130 K. In Figures 3, 5, 7 and 9

386
.06

UJ

.04-

.02

-.02

69^

i SQ

-.04

20 30 40 50 60

POINT NUMBER

Figure 2. Haynes-Hiza densities compared to DRS densimeter for methane.

this density difference is shown for the methane

fillings only and as a function of the order in which the data were acquired. The different

symbols are for the different fillings.

Figures 4, 6, 8 and 10 show the density

differences as a function of the density measured

by the DRS densimeter. The different symbols are

for the different compositions shown in table I.

Table I.

1 . Methane

2 Methane

Methane + 1% nitrogen

3. Methane

^ Methane

Methane + 2% nitrogen

5. Mixture

Mixture + 2% nitrogen

6. Methane

Graph Symbol

The results of the densimeter tests are re- ported in more detail in Reference 2.

Vibrating Cylinder Densimeter

In Figure 3 the percent density differences

for pure methane, shown as a function of the order

of the data acquisition, show a run-to-run shift of

about 0.1%. The calibration of the densimeter

was derived from these data. In Figure 4, the percent density differences for all the data are

shown as a function of density. The density dif- ferences decrease slightly as the density in- creases for both the LHG densities and methane

densities. The slope can be removed either by

adding a temperature-dependent term or a 1/f- dependent term to Eq. (1). This instrument has Sufficient precision to measure densities to within ^_ 0.1* with a proper calibration.

Vibrating Plate Densimeter .

In Figure 5, the percent density differences

for methane as a function of the data acquisition

show filling-to-filling shifts of the order of

+ 0.1%. The calibration of the densimeter was derived from these data.

The manufacturer's calibration was aone at room temperature in heavy fluids and showed a 1.62

bias with measurements at cryogenic temperatures

for these measurements. In Figure 6, the percent

density differences as a function of the density

are shown for all the data. Addition of nitrogen

to the methane fillings produced a detectable

offset in the densimeter reading. This densimeter

has sufficient precision to measure density of

these fluids to within + O.U with the proper

calibration.

Capacitance Densimeter

In Figure 7, the percent density differences

for methane as a function of the order of data acquisition for the capacitance densimeter sbow filling-to-filling offsets of about + 0.1%. The calibration supplied by the manufacturer vias used

for the data analysis and the disagreement between

this densimeter and the DRS densimeter is 1% for methane.

The percent density differences as a function

of the density are shown in Figure 8. The shift

of the density reading with composition ranges

from -2.4S for the LNG containing 2% Nj filling to IS for the pure methane fillings. These shifts

are in reasonable agreement with the shifts cal- culated by Giarratano and Collier.' The density

dependence of the density differences can presumably

be removed by adjusting the calibration equation. These results indicate that the composi tion must

be known to obtain the full precision of this densimeter.

3B7
Displacem ent Densimeter

In figure 9, the percent density differences

for methane as a function of the order of data acquisition are shown for the displacement den- simeter. For the analyses, the factory calibra- tion vjas used. Data for the first, third and fourth methane fillings show no apparent shift in calibration. The calibration was adjusted for the fifth filling. The downward shift of the cali- bration in the second filling was accompanied by noise in the density readings. The DRS densimeter readings were also more noisy, though they showed

no apparent calibration shift. The reason for the additional noise and calibration shift for the displacement densimeter is unknown. The factory

calibration gave a density usually about 0.05/J lower than the DRS densimeter reading.

The density differences as a function of density are shown in Figure 10 for all the data. The data below -0.08% are the data for the second

CH,, filling and the data for the subsequent addi- tion of Nj. Even then, all the data are within

the manufacturer's specified accuracy of +_ Q.2%.

4. Henins, I. and Bearden, J. A., "Silicon

Crystal Determination of the Absolute Scale of X-Ray Wavelengths," Phys. Rev. 135, A890

(1964).

5. Goodwin, R. D., "The Thermophysical Properties of Methane, from 90 to 500 K at Pressures to 700 Bar," NBS Tech. Note 653 (Apr. 1974).

6. Haynes, W. M. and Hiza, H. J., "Measurements

of Orthobaric Liquid Densities of Methane,

Ethane, Propoane, Isobutane and Normal Butane,

J. Chem. Thermodynamics 9, 179 (1977).

7. Giarratano, P. J. and Collier, R. S., "Evalu- ation of Capacitance Densitometry by Exami- nation of the Relationships between Density, Dielectric Constant, Pressure and Temperature for LNG Mixtures," I and EC Process, Design and Development 1_6, 330 (July 1977).

CONCLUSIONS

All the densimeters tested arc sufficiently

precise to use in LNG density measurements; al- though a composition input is required to get the best results from a capacitance densimeter. This work has not established the stability and relia- bility of these instruments over a long period of use in the field, but that could best be estab- lished by periodic review of densimeter perfor- mance in field use.

The most serious problem found is the lack of suitable calibration for low-temperature use. Only one densimeter was accurate to within the manufacturer's specified uncertainty and that instrument apparently could be used to a higher

degree of accuracy with a better calibration.

The factory calibration and stability checks of these instruments might best be done by com- parison measurements to a transfer standard or portable standard. Development of such standards

will be the next phase in the continuation of this work.

REFERENCES

1. Siegwarth, J. D., Younglove, B. A. and LaBrecque, J. F., "Cryogenic Fluids Density Reference System: Provisional Accuracy

Statement," NBS Tech. Note 698, (Oct. 1977).

2. Siegwarth, J. D., Younglove, B. A. and LaBrecque, J. F., "An Evaluation of Commercial Densimeters for Use in LNG," NBS Tech. Note

697 (Oct. 1977).

3. Bowman, H. A., Schoonover, R. M. and Jones,

M. v., "Procedure for High Precision Density Determinations by Hydrostatic Weighing," J. Res., NBS C, 71_C, 178 (1967).

388

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390 F-6
J. A. Brennan

National Bureau of Standards

Bou]der, Colo. WORK on inipro\1ng LNG flow meas- urement is being done under the sponsorship of the Pipeline Research Committee of the American Gas Association. This includes development of a method of testing flowmeters for use

in large-diameter LNG pip>elines and

on densitometers for use in conjunction with volumetric flowmeters to give mass-flow information. Answers to two basic questions are being sought. One is whether water

calibrations can be used to predict flowmeter performance in LNG service. The second is whether flowmeter performance in LNG measurement

can be determined in facilities where LNG is totally vaporized and comparisons then made between the liquid and gas-flow measurements.

Affirmative answers to both questions would be indicated by computing

an LNG meter factor based on a water

calibration and then demonstrating

good agreement between LNG flow measurements and the vaporized gas- flow measurements. Based on the data obtained thus far.

Based on paper, "LNG Flow Measurement,"

presented at the ASME Energy Technology

Conference, Houston, Sept. 18-23, 1977.

it appears possible to answer the two

basic questions affirmatively, provided

uncertainties of about it2Cc are toler- able. As more data are obtained on

both liquid and gas-phase measurements, it may be possible to reduce

the uncertainty. LNG flow measure- ment has the potential of being a much easier measurement to make

than measurements with orifice flow- meters in the gas phase. This is possible since: L One liquid flowmeter has about

three times the flow range of an ori- fice flowmeter.

2. Gas measurements are quite

sensitive to pressure and temperature which can fluctuate broadly

18.9%/MPa (145 psi), and 0.18%/°C.

respectively.

3. Liquid measurements are sensitive to temperature, but the temperature remains almost constant (0.35%/°C.).

4. Liquid measurements are in- sensitive to pressure fluctuations

0.29%/MPa (145 psi). Of course, good densitometers could

eliminate the last three problems. There appears to be progress in these

areas. The main problem remains in the proving of large LNG flowmeters. The work being done is a good start, but a much broader base is needed to

Fig. 1 LNG peak-shaving facility

Vortex- shedding flowmeter

6x8

Pressure,

Pressure | TemperotiJie ^

Sx6

Voporiier

To p'Ccfine

Colorimeter GrovHomeler

TejTiperature

Pressure, AJ>

About

2.76 !<?o (400 psi)

Figs. 2 and 3 Temperature change vs. time

Liquid temperature Gus temperoture

-157

I-25I)

FT3.2

-158

(-253)

-159

(-255)0 0.4 0.8 1i

Elapsed time, 1 0* set

50

(122)

40

(104)

30

(86)

20

(63)

10

(50)

0

(32)

-10

(14)0

Frg, 3

0.4 0.8 u

Elapsed time, 1 0' sec

168 G-1THE OIL AND GAS JOURNAL —JAN. 30, 1978
Fig. 4 Flow-rate comparison

60' (127)

50

(105)

40

(85)

30

20

10

(21)

(gas vs. liquid)

0.4 0.8 1.2

Elapsed time, 10^ set

Meter comparison

(sonic vs. vortex sliedding)

• 1

Fig. 5

40 eo 120 160

1623) (1.24(,) (l.e.'O) (2,493) Volume flow fc.'e, l./soc (gpf.i)

OG) /

predict meter performance with confi- dence. Problems. Ttiere are tv.'o main

probleni areas associated with flow measurement of LNG. The first one is the lack of accurate calibration facil- ities—especialli' for large-diameter

flovmieters. Presently, only tv/o accurate cryogenic flow facilities are

operating in the U.S. One is at the National Bureau of Standards (NBS). The other is at the Linda Div. of Union

Carbide.

' Both facilities normally use liquid nitrogen as the test fluid, although

other liquids are possible. There is also an LNG flow facility at NBS, but

tills facility is not of the same quality as the nitrogen facility and cannot be used for high-accuracy calibration work. All three facilities are limited

to maxim.um flow rates of 13 or 19

l.Asec (200 or 300 gpm). The second major problem is the lack of information on surrogate fluid calibrations for the flov/meters pres- ently being used in LNG. If it could be shown that accurate correction factors could be applied to meter factors determined from a water calibration

to give the meter factor in LNG, then

the need for large LNG flow facilities would not exist. Unfortunately, there has not been enough v/ork done in this area to establish the validity of such a pro- cedure. Ttiis area is beiiig investigated as pari of the work described in this

article. Test procedure. To circumvent the

lack of LNG flov^meter test facilities, an alternative procedure was established based on NBS's liquid-nitrogen flow facility at Boulder, Colo., and the water facility at Gaithersburg, Md.

Starting v/ith small (2 and 4-in.) flowmeters that could be tested on

both facilities, a relationship was

determined for the change in meter

factor from water to liquid nitro- gen. The 4-in. flowmeter was then in- stalled in an LNG peak-shaving facility where its measurements were compared with measurements made on

the vaporized gas usiiig conventional

orifice flowmeters. The flowmeter selected was a vor- tex-shedding type. The selection was

based on an extensive flowmeterevaluation program conducted at NBS,

cosponsored by NBS and the Compressed Gas Association. Other flow- meters could have been selected. But, based on information available at the time on both flov/meter performance

and potential problems associated with

the measurement of LNG, the vortex- shedding flowmeter was selected as

the one offering a good potential for success and a reasonable potential

for scaling to large si.zes. Test installation. Little data were

obtained on LNG with the 'J-in. flow- meter because of the demand schedule on the pea!;-shaving facility. Very little control could be exercised over the

test parameters since the facility had

to operate on demand and at flow rates and time intervals specified by the need for gas at the time. This flowmeter was half the size of the facility piping and could not be left installed during the high-demand portion of the sendout season. The data obtained did not indicate any major difficulties with the pro- cedures, hov/ever, so the 4-in. flow- meter vras replaced with an 8-in. meter. This larger meter v/as the same size as the facility piping. Therefore, it did not restrict the sendout capacity and could be left installed throughout the season. The size increase was a logical step

to test the adequacy of the overall

test procedure, also. It was also an

important step sir.ce no crj'ogenic cali- bration was possible on the larger flowmeter—only a water calibration preceded the LNG testing. Fig. 1 shows the layout of tlie LNG

l>cak-shaving facility where the flow- meter testing was performed. This

facility is ov.'ned by a private company which was testing a sonic flov;- meter in the same LNG line. As part of this program, data from

both flov.'meters wove recorded simul- taneously on magnetic tape. The temperature and pressure of the LNG

were also recorded for calculating

density. During the first year of testing, some unexplaiPiCd shifts occurred from

one test to another.-' No explanation

for these shifts could be found so additional instrumentation was added to the gas-phase measurements to per- mit recording the fiow data on magnetic tape. THE OIL AND GAS JOURNAL —JAN. 30, 1978 173 G-2
Both , liquid and gas measurements

were then returned to NBS for analysis. Before the addition of the recordings on the gas phase, the in- formation was manually read from

facility circular-chart recordings. Flow-rate computations. Liquid flow

rates were computed from these equations:

Ql = f/k

Qgl = QhplJpO

(1)

(2)

where: Ql = liquid flow late, l./sec

f = flowmeter output, pulses/sec k = meter factor computed from

water calibration, pulses/1. Qgl = equivalent gas-flow rate,

mVsec

PL — LNG density, kg/1. PC = vaporized gas density, kg/m'

LNG densities were calculated from

the composition determined by gas

analysis from a sample taken of the vaporized LNG using a computer pro- gram developed by McCarty.* Gas

densities were calculated according to American Gas Association (AGA)

recommended practices.'^ Other than gas density, there are

three critical parameters in these cal- culations: (1) meter factor, (2) gas

composition, and (3) liquid temperature at the flowmeter. Pressure of the liquid at the flowmeter is of sec- ondary importance. The meter factor was to be verified in this work. Composition obviously depends on

obtaining a representative sample and

then analyzing it accurately. The subject of sampling, beyond the scope of

this article, is an important consideration. A check on the composition determination was obtained by calculating the heating value and specific gravity of the gas from the analysis and comparing the result with the measured values from a calorimeter and gravitometer. Both instruments require a rep- resentative sample. But, since the samples were continuous, taken from

a different location, and used a dif- ferent technique, any errors involved were probably different from those associated with the sample taken

for the gas analysis. Since the two

heating-value determinations agreed

within the accuracy of the instrumentation, it was concluded that no large sampling errors were present. Liquid densities are a strong function of temperature—about 0.35 %/K.

(or °C.)—but fortunately temperature

=s quite steady throughout a test. Fig.

2 shows the variation in liquid temperature over a 4-hr test interval. Other tests for longer periods and a

large variation in flow rates had similar temperature traces. Errors from this source can be made small by good installation and

cahbration techniques. To show more

detail in Fig. 2, the start-up and shutdown were cut off at 116° K. (-251° P.). Gas-f!ow rates were calculated ac- cording to Equation 3:^

Qg = F,F.YFp,F,,F,rFgFpvF„F,F,

(h. pf)« (3)

where: Qg = orifice gas-flow rate Fb = basic orifice factor Fr = Reynolds number factor Y = expansion factor Fpb = pressure/base factor

Fib = temperature-base factor

Ftf = flowing temperature factor F- =: specific gravity factor Fpv = supercompressibility factor Fm = manometer factor Fa ~ orifice thermal expansion fac- torFe = gauge-location factor h„ = differential pressure

P( = absolute static pressure

In Equation 3, several parameters

are constant for a particular installation. Pressure and temperature para- meters are not constant, however, and

the calculation is quite sensitive to changes in them.

Fig. 3 shows the gas-temperarare

fluctuation during the same test as

that in Fig. 1. This is a relatively steady temperature profile, too. \Vhen

flow conditions were changing, the gas temperature would fluctuate over even

wider ranges and on short time

intervals. The possibility for errors in calculating results from widely varying

parameters is obviously increased and

The author . . James A. Brennan has been associated with the Cryogenics Division

of the National Bureau

of Standards for about 20 years. He currently

is v/orking on projects investigating instrumentation for use in measuring the heating

value of LNG flowing

in a Dipeline and the use of transfer stand- ards in the custody

transfer of cryogenic liquids. Both projects

Involve measurements of flow, density, temperature, and pressure. Brennan's experience

includes flow of cryogenic liquids into a vacuum, pipeline cool-down problems, and

bearings for low-temperature applications. He

is the author or coauthor of over 20 publications on cryogenic subjects, and holds a BS degree in mechanical engineering (1958) from the University of Colorado.

I ^

James A. Brennan

can be significant since a 1° C. error

results in an 0.18% error in flow rate. Similar problems can exist with gas- pressure fluctuations where errors

of 18.9'^e/MPa (145 psi) result from

errors in pressure measurement.

During start-up, a high-temperature

spike occurred. It has been deleted from Fig. 3 so the remainder of the

test can be seen in more detail. Fig. 4 com.pares flow rates deter- mined with the &-in. vortex-shedding flowmeter in LNG v/ith a 9-in. orifice meter in a 16-in. pipe in vaporized gas. During this flow test, flow rate was

relatively constant throughout the run. The comparison is within the measurement uncertainty of the two flow measurements except during start-up, shutdown, and the rate change just before 12,000 sec elapsed time. Disagreement during changing flow

rates is not considered serious since there effectively is a variable-capacity capacitance in the gas-phase portion of the system. During this test, only one orifice flowmeter was re- quired. Gas temperature and pressure were relatively steady. Therefore, the conditions for good comparisons were

favorable. During later tests, up to three ori- fice runs were required, and wide

fluctuations occurred in gas temperature and pressure. Since the data

analysis on the later tests is not yet complete, no definite statements are

possible. But from a preliminary

analysis, the comparison still looks to be within the experimental uncertainty. At high flow rates, it appears the

liquid measurements were consistently higher than the gas measurements.

Possible explanations for this trend must await final data analysis. The

deviation shown in Fig. 4 was calculated from Equation 4:

Deviation (%) = (Qgl - Qg) X 100/Qg (4)

Fig. 5 shows a comparison of the two liquid flowmeters. The deviation

sho'OTi is that of the sonic flowmeter from the vortex-shedding flowmeter.

It was calculated from the equation,

Deviation (%) = (Qs — Qvs)

X lOO/Qvs (5)

where: Qs = flow rate indicated by sonic flowmeter

Qvs = flow rate indicated by vortex flowmeter

At flow rates above about 50 l./s (790 gpm), deviation between the two

174 THE OIL AND GAS JOURNAL —JAN. 30, 1978 G-3
flowmeters is nearly constant. At

lower flow rates, the sonic flowmeter became erratic. The fact that the sonic flowmeter exhibited a positive deviation means that it indicates an

even larger discrepancy when compared with the gas-flow measurements.

Since the sonic flowmeter was not

originally part of this program, no

history had been documented. So far as is known, no prior cryogenic flow data were obtained, and the meter

factor was calculated by the manufacturer from dimensional and fluid- properties data. As more data are

obtained, these calculations can obvi- ously be refined. Densitometers. An obvious improve- ment to this measurement method

would be addition of a direct-reading densitometer. Several promising in- struments are available. One has been

used in flowing liquid nitrogen with encouraging results.' The densi- tometer was a vibrating-plate type. Recently, that type, along with a

vibrating-cylinder and a capacitance

type, have been tested in nonflowing

liquid methane and LNG-type mixtures. Both vibration types of densi- tometers have demonstrated ability

to indicate densities to v.'ithin about 1/4%.

The cap.^citance densitom.eter also shows promise, provided the range of composition is knovm and does not

fluctuate too much. All three types are suitable for in-line use in flowing streams, although the effect of fluid velocity is not well documented.

Refeiences

1. Close, D. L., "Cryogenic Flowmeters —Today," Cryogenics and Industrial Gases,

Vol. 4, Augiist 1969, pp. 19-23.

2. Dean, J. \V., Brennan, J. A., and Mann,

D. B., "Cryogenic Flow Research Facility of the National Bureau of Standards," Advances in Cryogenic Engineering. Vo'. 14, 1968, pp. 299-305.

3. Brennan, J. A., LaBrecque, J. F., and Kn^ebone, C. H., "Progress Report on Cryogenic Flov/;i\eten"ng at the N.ntional Bureau

of Standards." Instrumentation in the Cryogenic Industry, Vol. 1. Proceedings of the

First Bicanial Symposium on Cryogenic In- strumentation, 31st ISA Conference & Exhibit, Houston, Oct. n-14, 1976.

4. McCarty. R. D., "A Comparison of Mathematical Models for the Prediction of LNG Densities," National Bureau of Standa.-ds Interagency Report 77-867, 1977.

5. Orifice Metering of Natural Gas

Measurement Committee Report No. 3, American Gas .Association, l.'ilS Wilsou

Blvd., Arlington, Va., 1969 Revision, 93 pp.

6. Brennan, J. A.. Stokes. R. W., Kneebone, C. H., and Mann. D. B., "NBS-CGA

Cryogenic Flow Measurement Pi-ogram," ISA Transactions, Vol. 14, No. 3. 1975, pp. 237-247

7. Siegwarlh, J. D., Younglove, 3. A., and

LaBrecque. J. F., "An Evaluation of Cryogenic Densimeters for Use in LNG," National Bureau of Standards Technical Note

697, July 1977. THE OIL AND GAS JOURNAL —JAN. 30, 1978
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 78-894

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE LIQUEFIED NATURAL GAS RESEARCH AT THE NATIONAL BUREAU OF

STANDARDS

5. Publication Date September 1978

6. Performing Organization Code 736

7. AUTHOR(S)

D. E. Diller, Editor

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 7360104

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

See block 16 below.

13. Type of Report & Period Covered Semi-Annual

Jan 1 - June 30, 1978

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant bibliography or literature survey, mention it here.) Thirty-one cost centers, supported by six other-agency sponsors in addition to NBS, provide the basis for liquefied natural gas (LNG) research at NBS. During this

six-month reporting period the level of effort v/as over 20 man-years /year with funding

expenditures of over $500,000. This integrated progress report, to be issued in

January and July, is designed to:

1) provide all sponsoring agencies with a semi-annual report on the activities

of their individual programs;

2) inform all sponsoring agencies on related research being conducted at the

Thermophysical Properties Division;

3) provide a uniform reporting procedure which should maintain and improve

communication while minimizing the time, effort and paperwork at the

cost center level.

The contents of this report will augment the quarterly progress meetings of some

sponsors, but vzill not necessarily replace such meetings. Distribution of this

document is limited and intended primarily for the supporting agencies. Data or other

information must be considered preliminary, subject to change and unpublished, and

therefore not for citation in the open literature .

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper neme; separated by semicolons

)

Cryogenics; liquefied natural gas; measurement; methane; properties; research.

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