A 11 ID

5

EFFECTIVE THERMAL CONDUCTIVITY OF A GLASS

FIBERBLANKET STANDARD REFERENCE MATERIAL

David R. Smith

Jerome G. Hust

Lambert J. Van Poolen

Thermophysical Properties Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

HQC

100

.1156

SI-JAW

1981

February 1981

NBSIR 81-1640

r <r *

national buhjcad

Or 8TANBAJU)*

UllAIT

MAY 1 3 1»'

EFFECTIVE THERMAL CONDUCTIVITY OF A GLASS

FIBERBLANKET STANDARD REFERENCE MATERIAL

David R. Smith

Jerome G. Hust

Lambert J. Van Poolen

Thermophysical Properties Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

February 1981

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldridge, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
Ttt > * UJ

• 5K S .£ Y«f
CONTENTS

Introduction

Page

1

Apparatus and Specimen Characterization 1

Results .............................. 3

References (Annotated Bibliography) ................ 12

iii

Effective Thermal Conductivity

of a Glass Fiberblanket Standard Reference Material

David R. Smith, Jerome G. Hust, and Lambert J. Van Poolen

This paper* describes the results of thermal conductivity

measurements at temperatures from 84 K to 360 K on a glass fiberblanket insulation which is intended to be a Standard Reference

Material (SRM) . The measurements were performed in an atmosphere

of dry nitrogen at a pressure near 84 kPa (630 mm Hg) . The

results are analyzed and compared to literature data for similar

material. An annotated bibliography of literature sources is

included

.

Key words: Glass fiberblanket; insulation; low temperature;

standard reference material; thermal conductivity.

Introduction

As part of the National Bureau of Standards - Department of Energy Program

to establish insulation Standard Reference Materials (SRM’s), work is continuing on various candidate materials. The results on SRM 1450 (glass fiberboard)

were reported earlier [l]. Results of measurements are reported here for a

\ specimen of a glass fiberblanket insulation for specimen temperatures covering

the range from 84 K to 360 K, in an atmosphere of dry nitrogen gas at 84 kPa

(630 mm Hg) , local atmospheric pressure.

Apparatus and Specimen Characterization

A commercial guarded-hot-plate thermal conductivity instrument was extensively modified [2] to permit efficient use of cryogenic or refrigerated coolants, to obtain greater stability of controlled temperatures, and to achieve

*This work was done for the Department of Energy, Oak Ridge Operation, Oak

Ridge, TN 37830, under Interagency Agreement DoE No. DE-AI05-780R05965

.

1
lower imprecision and uncertainty of measurements. This apparatus was designed

to measure heat transfer through a pair of specimens surrounding the horizontal

hot plate in the typical double-sided guarded hot plate configuration (ASTM STM

C-177)

.

The pair of specimens studied were disks of nominal 10 cm (4 in) diameter

and 2.6 cm (1.0 in) thickness. They were cut from larger slabs measuring

approximately 58 cm square as received from the National Bureau of Standards,

Office of Standard Reference Materials stock. The pair was chosen on the basis

of near equality of area densities (0.0381 g/cm^ and 0.0383 g/cm^). The

thickness, Ax, of each specimen was determined during the conductivity

measurement by three stainless steel spacer tubes positioned at three

equidistant points around the perimeter of the guard material. The guard

material was similar to that of the specimens with an inside diameter of 10 cm

(4 in) and an outside diameter of 20 cm (8 in). The measured thickness was

2.59 cm and the resulting volume density was 14.75 kg/m^. This thickness was

corrected for thermal expansion of the spacers (less than 0.3 percent).

All hot plate/cold plate surfaces facing the specimens were black anodized

aluminum. The cold surfaces were electrically heated, temperature-controlled

plates, cooled by resistive thermal contacts with fluid-cooled copper plates;

thus the cold surfaces of the specimens could be brought to a temperature near

that of the coolant, or raised in temperature, as desired. The main heater

(metered section) was a disk 10.16 cm in diameter separated by a 1.6 mm gap

from the annular guard of 5.1 cm width. A concentric, cylindrical outer guard

surrounded the stack of auxiliary heaters, specimens, and main heater. It

established a temperature gradient approximating that of the stack about 2 cm

away from the stack edge surfaces.

2
Temperature controllers were used to regulate conditions in the inner and

outer guards and to establish steady temperatures in the auxiliary heaters at

the cold sides of the specimens. The offset signal for the inner-guard controller was developed by a 20-pair thermopile of type E thermocouples, with

alternate junctions on opposite sides of the gap separating the main and innerguard heater plates.

Type K thermocouples (32 gauge) for determining temperatures of the specimen faces, positioned at the center and near the gap surrounding the main heater, were varnished to the surfaces of the hot and auxiliary plates over a

length of 15 cm. These thermocouples were also thermally tempered by means of

15 cm of wire wrapped and varnished to copper lugs attached to the periphery of

the hot and auxiliary plates.

Type K thermocouple wire was calibrated using a calibrated platinum resistance thermometer and baths of liquid helium, liquid nitrogen, dry-ice-andalcohol, ice-water, room-temperature water, and boiling water. The departures

from the standard tabular values* of emf vs. temperature were represented by a

3-term polynomial and a corrected calibration curve was formulated for the

particular spools of thermocouple wire used.

The dc power, Q, for the main heater was obtained from a constant current

power supply of better than 0.01 percent stability and accuracy. The power in

the metered heater was found from the product of voltage drop, V, across the

heater and the current, I, through the heater.

Results

Measurements of heat flow and of temperatures of the hot and cold surfaces

were performed at mean temperatures from 95 K to 350 K with temperature

thermocouple Reference Tables based on IPTS-68, NBS Monograph 125, March, 1974.

3
differences of about 25 K (gradient approximately 1 deg/mm). The metered area

was taken to be that contained within the 10.32 cm diameter circle

including the main heater and one-half of the surrounding gap. The area

through which the metered heat energy flows through the two matched specimens

is 2^. This area was corrected for thermal expansion (less than 0.7 percent).

The mean thermal conductivity , ¥, was computed according t0 ^ = ^

=

( t^tJ*

where T

? and T^ are the average hot and cold side temperatures

,

respectively. The resulting data set of values k, Q, T]_, and T2 were then

functionally represented using a thermal conductivity integral (TCI) fitting

technique* to yield the thermal conductivity as a continuous function of

temperature over the range from the lowest value of T^ (84 K) to the highest

value of T2 (360 K) . This resulted in the values of the parameters , Aj

4 . in the equation k = £ A.T . This technique is valid only to the extent

i=l 1 that the mechanisms of heat transfer are conductive in nature (as opposed to

direct radiation or convection). Deviations from this condition can be detected by searching for systematic trends in the deviations of the fitted data as a

function of boundary conditions. This search will be conducted on more extensive data to be published later.

The values of k vs. temperature obtained by means of this technique for

the specimens are given in Table 1 and plotted in Fig. 1 (solid line). The

values of ¥ are also plotted in Fig. 1 (circles) at the mean temperature, T.

*Hust, J. G. and Lankford, A., Comments on the Measurement of Thermal Conductivity and Presentation of the Thermal Conductivity Integral Method, to be

published

.

4
The fact that the mean values of thermal conductivity, k, are consistent with

the solid line for k at T is indicative of the absence of appreciable nonconductive heat transfer mechanisms, i.e., direct radiation and convection.

Deviations between k and k at T can also be caused by non-linear behavior of k

vs. T for just conductive heat transfer, but, in this case k vs. T is nearly

linear. Table 2 gives the coefficients, A^, and the range over which the

fitted curve is valid. The TCI deviations, (TCI0 b s - TCIca ^ c ) x lOO/TCIo^g,

between the data (obs) and the fitted (calc) curve are given in Fig. 2 as a

function of mean temperature. The horizontal bars indicate the temperature

range for each measurement and the range of the TCI. A three term polynomial

fit showed large systematic deviations from the data but the four term

polynomial exhibited mainly random deviations. The remaining small systematic

deviations (approximately +1/2 percent) were essentially unchanged from a four

terra to a seven term polynomial. Further analysis is planned on other data

sets to ascertain if these systematic deviations reflect real behavior or

experimental error. At about 320 K two triplets of points are shown in Fig. 2

which differ appreciably from the mean (+ 3 percent). These data are the

result of running the apparatus in the single-sided mode, i.e., each triplet is

a measure of only one or the other of the two specimens. Further analysis is

required to determine if these deviations are caused by specimen variations or

by differences in the apparatus configuration.

Other investigators [3-14] have reported similar trends in the dependence

of k on temperature for glass fiber insulations over a wide range of densities

including our value. The characteristic differences of these insulations,

5
such as binder or lubricant content, fiber size or atmospheric pressure

actually present at each laboratory, are not known in great enough detail to

permit definitive statements about the agreement or disagreement between

results. Comparisons of literature data [5,7,10,12,14] to our equation are

illustrated in Fig. 3. The uncertainty of the present results is estimated to

be + 1 percent. Research on this material is being continued to determine the

effects of specimen density and fill gas species and pressure on the effective

thermal conductivity. Other parameters such as thickness, plate emittance, and

heat flow direction will also be examined to further elucidate the nature of

the heat transfer mechanisms present.

6
84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

110

120

130

140

150

Table 1

conductivity of glass fiberblanket versus temperature

on the fitted results of the present investigation.

k

(mW/m K)

8.90

9.01

9.12

9.24

9.35

9.46

9.57

9.68

9.80

9.91

10.00

10.14

10.25

10.36

10.48

10.59

10.70

11.85

13.00

14.18

15.37

16.59

k

T (K) (mW/m K)

160 17.83

170 19.10

180 20.40

190 21.74

200 23.12

210 24.56

220 26.04

230 27.59

240 29.20

250 30.89

260 32.67

270 34.53

280 36.49

290 38.57

300 40.76

310 43.08

320 45.54

330 48.15

340 50.92

350 53.87

360 57.00

7
Table 2

Coefficients of the Least-Squares Fit: k

Aj_ = 0.986120 x 10_1

A2 = 0.121313 x 10~ 3

A3 = -0.562714 x 10“ 6

A4 = 0.190726 x 10-8

Range: 84K < T < 360K

4

£

i=l

8
CO

CO | (U 5 U S-i O *H 3

jr o -u

co CO « l-l

*.ui/mw ‘ aii

A

iio na nod ivi/vaaHi

0

Figure

1

Thermal

conductivity

data

for

glass

f

iberblanket

.

Solid

line

results

of

least

squares

fit

of

thermal

conductvity

integrals

cles

are

mean

k

values

plotted

at

the

mean

experimental

tempe
©

I

I 0 H (U rt -u I O CO c 0) 0 CO 0

o cu

*

ui

K

3

H

<

&

ty

a

yj

H

% ‘NO! 1V S A 3 Q

10

Figure

2

Deviation

of

observed

thermal

conductivity

integrals

(TCI)

fr<

culated

values

of

TCI

for

glass

f

iberblaaket

.

Circles

show

m

perature

and

horizontal

bars

indicate

temperature

span

of

the
*.UI/MUI ‘AllAllOnaNOO 1VIA8U3HJL

n

Figure

3

Comparison

of

literature

data

on

glass

fiberblanket

specimens

ranging

in

density

from

11

kg/m^

to

40

kg/m^

to

our

present

results.
References (ANNOTATED BIBLIOGRAPHY )

The references for this document and other papers of interest have been

presented in the form of an annotated bibliography as an aid to the reader.

An extensive search has been made of the published literature relating to

the effective thermal conductivity of fibrous glass insulation, in the range of

densities characteristic of glass f iberblanket . Of special interest to the

authors are studies relating to the dependence of k on temperature, density,

gas pressure and species of fill gas. The format, given below, for this

bibliography is designed to present the conclusions of each paper in a concise manner. Not all papers fit the format in its entirety but the format includes

all the relevant types of information found in the majority of papers studied.

It is found that authors' abstracts are not sufficiently detailed in

describing specific types of specimen characterization, experimental or theoretical studies and conclusions; therefore abstracts have not been listed in

this work.

The units shown in the annotated bibliography are those given in the

original article. SI units have been added in parentheses for convenience.

12
FORMAT FOR ANNOTATED BIBLIOGRAPHY

AUTHOR, TITLE, CITATION

REFERENCE

ANNOTATION

PURPOSE

SPECIMEN

a) Thickness; b) Density; c) Fill Gas Species/Pressure; d) Fiber Diameter; e) Bonding Agent; f) Other Characterization

APPARATUS

a) Type; b) Heater Dimensions: Overall/test; c) Plate Orientation or Radial Axis; d) Thermometry; e) Calibration; f) Remarks

THEORY

a) Physical/Mathematical Models Including Assumptions; b) Calculational

Techniques; c) Results

DATA

a) Temperature Range/Gradient; b) Content of Tables, Figures, and Equations; c) Uncertainty/Imprecision; d) Disputable Corrections to Measurements by Authors; e) Errata (by Author or Reviewer)

ANALYSIS

a) Comparisons; b) Heat Transfer Mode Separations; c) Conclusions

13
[1] Smith, D. R. and Hust, J. G. , Measurement of Effective Thermal Conductivity

of a Glass Fiberboard Standard Reference Material, to be published in

Cryogenics; sponsor report No. 773.30-80-2.

PURPOSE

To determine effective thermal conductivities of glass fiberboard

materials over a temperature range from cryogenic levels to just above

ambient and to develop this material as a standard reference.

APPARATUS

a) guarded hot plate; b) 8 inches (20 cm)/4 inches (10 cm) dia.; c)

horizontal; d) type K (Cr-Al) thermocouples; e) calibration measurements

agreed to within 1.5%; f) apparatus operated over the range approx. 80 to

350 K.

SPECIMEN

a) 2.59 cm (1 in); b) 123 kg/m^; c) N 2 /atmospheric

THEORY

a) k vs T (four term polynomial); b) thermal conductivity integral

technique used to fit and calculate k vs T; c) representation of data + 0.4% over temperature range.

DATA

a) 87-340 K/l-4 K/mm; b) Table 1 and Figure 1 - k vs T, Figure 2 - deviations from fit of thermal conductivity integrals, Figure 3 - k vs T

comparisons with literature data; c) + 1% overall

ANALYSIS

a) comparison to literature data

[2] Smith, D. R., Hust, J. G., and Van Poolen, L. J., A Guarded-Hot-Plate

Apparatus for Measuring Effective Thermal Conductivity of Insulations Between

80 K and 350 K ( to be published as an NBSIR)

.

PURPOSE

To describe in detail the modifications made to a commercial guarded hot

plate apparatus for use as a certification device.

APPARATUS

a) guarded hot plate; b) 8 inches (20 cm)/4 inches (10 cm) dia.; c)

horizontal; d) type K (Cr-Al) thermocouples; e) calibration measurements

agreed to within 1.5%; f) apparatus operated over the range approx. 80 to

350 K

14
[3] Allcut, E. A., An Analysis of Heat Transfer Through Thermal Insulating

Materials, General Discussion on Heat Transfer , Sep. 1951, IME/ASME pp. 232-

235, 486-487 (Inst. Mech. Eng., London, 1951)

PURPOSE

Study influence of radiation and convection on heat transfer in fibrous

insulation.

SPECIMEN

b) 1.25 to 3.5 lb/cu ft (20 to 56 kg/m ); c) air/0.4 to 80 in Hg (1.3

to 270 kPa)

APPARATUS

a) guarded hot plate; b) 8 inches (20 cm); f) enclosed in

pressure-vacuum tank

DATA

a)

b)

34 to 96°F/34 to 62°F difference (1 to 36°C/19 to 34°C difference)

Table 12

3,4,5

6

Figure 123

4

5 6,8

k vs density for glass wool batts

k vs p for air cell

k vs p vs T vs density for glass wool batts

% of total heat transmitted by convection

k vs density for various materials including mineral wool

k vs cell size for Styrofoam

k vs p for various materials

k vs p vs density for glass wool

(p/k) vs p for glass wool

convection vs p, and density for glass wool.

ANALYSIS

b) radiation effect is negligible in glass wool blankets exceeding 2 lb/cu

ft (32 kg/m'*) density; c) In cellular or granulated materials, k varies

almost directly with cell size.

15
[ 4 ] Allcut, E. A., Properties of Heat Insulating Materials, The Engineering

Journal, 514-520 (Nov. 1941)

PURPOSE

A discussion of the character of heat insulating material, the

difficulties in determining their relative value experimentally, the

effect of air spaces and surface resistance and the possibility of saving

fuel by taking advantage of solar radiation and heat stored in the

structure of the building itself. An appendix describes a microscopic

examination of a number of insulating materials.

SPECIMEN

a) 0.2 to 1.5 in (5 to 38 mm); b) 1.6 to 5 lb/cu ft (26 to 80 kg/m );

c) air/atmospheric; e) 5.5 ym

APPARATUS

a) guarded Hot Plate; b) 8 in (20 cm) square; c) vertical

DATA

a) 90°F/35 to 200°F/in (32°C/8 to 44°C/cm)

b) Table 1: k vs thickness (density) for three blanket materials (one

glass wool).

Table 2: Heat loss in insulated pipes.

Figure 1,2

3

46

8

9

11

14

Structure of different fiber boards.

Air leakage in rock wool

Air leakage in fiberboard, different densities,

k vs air pressure for various materials

k vs thickness

k vs density

k vs thickness

fiber-diameter distribution curve.

16
[5] Bankvall, C. , Heat Transfer in Fibrous Materials, J. of Testing and

Evaluation, JTEVA, 1(3), 235-243 (May 1973).

PURPOSE

Mechanisms of heat transfer are calculated theoretically, then verified

experimentally by measurements on glass fiber insulation in a specially

constructed guarded hot plate apparatus. The author claims the theories

give a complete and consistent explanation of the influence of the mechanisms of heat transfer on the effective thermal conductivity of fibrous

material

.

SPECIMEN

a) 0.5 to 5 cm; b) 15 to 80 kg/m^; c) air/10-

3 to 760 mm Hg (0.1 to 100

kPa); d) 5 ym; f) porosity, radiation coefficient.

APPARATUS

a) guarded hot plate, one-sided, rotatable; b) 35 cm diam; c) horizontal

THEORY

a) Fibers in layers at right angles to flow of heat; walls, fibers are "gray", non-transparent bodies; b) Two-phase open-pore model.

pL 0 k -- -, L0 =inter-fiber distance=TTD/4( 1-e)

eff gas

lc _ __ • Lo 1 gas pLo+ET

k

eq

.

fib

= 32(l-£) 2

sol

/w(3+-

k

eff rad

4GLT3 /(0' m

_1

+Lo(2/£

DATA

a) 0 to 56 °C; b) Figure 2:

4(l-e) )

6

78

9

10

11

,3m

Open-pore two-phase model.

Radiation coefficient, 0, vs porosity, £.

kfib vs porosity

8 vs £ for different temperatures.

Structural parameter, a, vs porosity, £.

£

g vs £

.

Radiational conductivity vs specimen

thickness.

12: k vs Tmean for d = 16.4 kg/m3, low (10“3 mm Hg)

pressure

.

13, 14: k vs pressure at Tm

= 30°C, d = 16.4 and

78.6 kg/m3

15: k vs Tm

at atmospheric pressure.

16: Mechanisms of heat transfer in glass fiber.

ANALYSIS

c) All mechanisms involved in transfer by gas must be considered, to be

correct in estimating contribution by gas to ke ff; d) Conduction in

gas contributes largest part of ke ff in range 15-80 kg/m3. Radiation

is of greatest importance at low density and leads to large k at low

density. Conduction of solids is an important contribution at high

density. Increasing temperature leads to larger k, especially at low

density where radiation is important.

17
[6] Bartoli, R. and Laine , P., Thermal Conductivity Measurements of Fiberglass

Panels at Different Temperatures in Various Atmospheres, Supplement to Bull,

of Int’l Institute of Refrig. (Paris) Annexe 1956-2, pp. 233-240 (1956).

PURPOSE

Measurements of thermal conductivity of fiberglass panels in various

gases, at different temperatures.

SPECIMEN

a) 5 cm; b) 33,88,120 kg/ia3

; c) air, C0£ , R-12; d) 12 x 10“^ m; e) none

APPARATUS

a) guarded hot plate; c) horizontal; d) copper-cons tantan thermocouples

DATA

a) -15 to +15°C/26 to 66 K/cm

b) Figures 2,3,4: k vs T, several densities

air: k^ = k2 = k 3 = kl = ko =

CO'

(33.8 + 0.208t)xlQ-3

(26.8 + 0. l45t)xl0-3

(26.3 + 0. 120t)xl0-3

(23.6 + 0. 185t)xl0-3

(18.3 + 0.080t)xl0-3

kCal/m .h . °C,

R-12: k2 = (12.0 + 0.100t)xl0-3

d| = 33 kg/m3

d

2 = 88 kg/m3 d

2 = 120 kg/m3

ANALYSIS

a) At 0°C

k (C0 9

) k (CO ) k

x (air) Uo/U » k2 (air) 0.69,

k

? (R-12)

k9 (air)

in good agreement with Verschoor and Greebler, (0.71, 0.71, 0.47, resp.)

at Tm

= 66°C.

and k'!g(air)

k lc (air)

k2c (air)

k3 c ( a ir)

(20.8 + 0.060t)xl0”3

(13.0 + 0.148t)xl0“3

(5.55 + 0.084t)xl0“3

(4.75 + 0.058t)xl0-3

kCal/m»h»°C

kCal/m*h»°C

kCal/m • h *°C

kCal/m*h*°C

k

2g k 3g

18
[7] Brendeng, E. and Frivik, P. E., New Development in Design of Equipment for

Measuring Thermal Conductivity and Heat Flow, Heat Transmission Measurements in

Thermal Insulations, ASTM-STP 544, pp. 147-166 (1974).

PURPOSE

This paper describes some of the recent developments in test equipment

design and operation.

SPECIMEN

a) 10 cm; b) 11,88 kg/m^; c) air/atmospheric; f) temperature

distribution; influences of convection, emissivity of plates.

APPARATUS

a) guarded hot plate; b) 0.4 m sq.; c) horizontal; d) PRT and thermocouples; e) measured reference material calibrated at National Physical

Laboratory (England)

DATA

a) -5 to 80°C

b) Figure 8: k vs Tm » glass wool and glass fiberboard, 11 and 88 kg/m^

9B: ke ff vs AT, glass wool

19
[8] Christiansen, R. M. and Hollingsworth, M. , Jr., The Performance of Glass

Fiber Insulation Under High Vacuum, Advances in Cryogenic Engineering , 4,

141-153 (Plenum, New York, 1960).

PURPOSE

Evaluate technique of partial removal of fill gas from fibrous insulation

to improve thermal performance. Study effective thermal conductivity vs pressure, density and fiber diameter.

SPECIMEN

a) 0.2-1. 8 in. (5 to 45 mm); b) 0.5-15 Ib/cu ft. (8 to 240 kg/m^); c)

air/2 10~4 mm Hg to 1 atm (0.03 to 100 kPa); d) 22,45,135, 480 microinches (0.55, 1.1, 3.4, 12 ym); e) heat felting or phenolic resin

APPARATUS

a) heat meter in bell jar; b) 12 in (30 cm) sq; c) vertical; d)

differential thermocouple; e) samples of known conductivity

DATA

a) 75°F/35 to 200°F/in (24°C/8 to 44°C/cm);

b) For a density of 4 lb/ft^ (64 kg/m ):

k(resid . gas + sol.) = 0.0037, k(rad) = 0.0065 at Tm

= 75°F (24°C)

k(resid. gas + sol.) = 0.0018, k(rad) = 0.0016 at Tm

= -180°F

(-118°C)

ANALYSIS

a) Figure 4: k vs pressure (vs fiber diam. vs density)

6: k vs fiber diam. (vs density, pressure)

7: Importance of insulation in blocking radiation

9: component separations

c) For 0.1 mm <_ p 100 mm Hg (0.01 to 13 kPa) , finer fiber and higher

density give lower k At low density and high p, optimum fiber diam. is

10“6 in (130 ym) . At low p, higher density not harmful.

Mean free path and average fiber spacing control k.

Optimum density 8 Ib/cu ft (130 kg/m ) at vacuum, 4 Ib/cu ft (60

kg/m^) at atmospheric pressure.

Existence of optimum fiber diameter, predicted by Larkin, confirmed,

because at very low p, k(res) is due to radiation and solid conduction.

When fiber insulation is present at moderately low pressure (0.1 mm, 10

Pa) k is as low as in high vacuum. Fiber insulation necessary to block

radiation between surfaces.

50

20
[9] Fournier, D. and Klarsfeld, S., Some recent Experimental Data on Glass

Fiber Insulating Materials and Their Use for a Reliable Design of Insulation at

Low Temperatures, Heat Transmission Measurements in Thermal Insulations, ASTM

STP 544, American Society for Testing and Materials, 223-242 (1974).

PURPOSE

To give theoretical criteria for onset of natural convection in open-pore

thermal insulators; measure k; measure permeability to flow of air; guide

wall design in minimization of heat transfer.

SPECIMEN

a) 24-28 mm; b) 8-135 kg/m^; c) air/atmospheric; d) 2.5, 3, 6, 12 pm;

f) TEL glass fiber, porosity .93-. 997

APPARATUS

a) guarded hot plate; b) 8 in (20 cm)/4 in (10 cm) dia; c) horizontal;

d) thermocouple

THEORY

a) right-angle parallelepipedic. , tight volume insulating cell,

horizontal/vertical orientations; onset of convective motion-filtration

Rayleigh Number > 40, for horizontal cells and Rayleigh Number/Aspect

Ratio > 4 in vertical cells; c)predict natural convection increases in

low temperature ranges

DATA

a) 123-300 K, 20-70 K/in (8 to 28 K/cm);

b) Figure 4: k vs density - fineness ratio as parameter

5-6: permeability vs density - fineness ratio as parameter

7-9: k vs Tmean , density as parameter

Other data relating to permeability and convection

ANALYSIS

a) to measurements in a different apparatus - 3% agreement; b) study

made of natural convection effect; c) for T < 200 K, density has little

influence on k - this is also true of fineness index; TEL glass fiber

material for k at temperatures below 198 K behaves similar to cellular

plastics and perlite; there are minimum acceptable densities for various

thicknesses, temperatures, and fineness ratios to prevent convection

21
[10] Hollingsworth, M. , Jr., An Apparatus for Thermal Conductivity at Cryogenic

Temperatures Using a Heat Flow Meter, ASTM STP 411: Thermal Conductivity

Measurements of Insulating Materials at Cryogenic Temperatures, 43-51, 1967.

PURPOSE

Evaluate a heat-flow-meter apparatus capable of measuring thermal conductivity of flat insulation specimens at cryogenic temperatures

SPECIMEN

a) 0.5 to 1 inch (1.2 to 2.5 cm); b) 0.85-3.2 Ibm/ft^ (14 to 51

kg/nr); c) air, atmospheric

APPARATUS

a) heat meter in bell jar; b) 12 x 12 (30 cm) in sq/6 x 6 in (15 cm) sq;

c) vertical; d) copper-constantan thermocouples

DATA

a) -125 to 120°F (-87 to 49°C); b) Figure 4, k vs Tmean for 4 different

densities

ANALYSIS

a) results compared with guarded hot plate data from 100-300°F (38 - 149°C); c) apparent good agreement with guarded hot plate data but no accuracy information given because no direct comparisons can be made,

i.e., at exactly the same test conditions

22
[11] Lander, R. M., Gas is an Important Factor in the Thermal Conductivity of

Most Insulating Materials, Part II, ASHVE Transactions, 151-168 (1955).

PURPOSE

Describes investigation of the reduction in thermal conductivity of common insulating materials by replacing air with gases of larger molecular

weight or fill gas.

SPECIMEN

a) 1 in (25 mm); b) 0.58, 0.78, 1.94, 3.80 lb/ft 3 (9, 12, 31, 61

kg/m3

); c) Air, C02 , R-12/0.1 ym of Hg to 1 atm (0.01 to 100 kPa)

APPARATUS

a) guarded hot plate; b) 12 in (30 cm) square; c) vertical; d)

thermocouples

DATA

a)

b)

100°F mean

Table 1:

2 : 3:

4:

5:

Figure 7:

9:

11 :

, 50°F/in (38 °C, ll°C/cm)

k vs fill gas; k(air) vs p; % reduction in heat transfer due

to gas substitutions

k vs p for air, C©2 R-12

k vs % mixture of (C02> R-12) with air

k vs T for various gases/densities

Calculated Different Modes of Heat Transfer for three

densities, three gases, vs T.

k vs T for glass wool in air, C02» R-12 for varying insulation densities

Gas transferred heat vs T for various fill gases

Heat transferred by radiation/conduction vs density for

various T's.

ANALYSIS

b) Fiber conduction/gas transferred heat (conduction)/radiation

c) Major mode of heat transfer is by the fill gas,

18 to 31% reduction in k if CO2 replaces air,

28 to 56% reduction in k if R-12 (CF2 CI 2

) replaces air,

Conductivity of glass wool is decreased for increasing density (amount

of decrease independent of fill gas).

For practical insulation, radiation is an important mode of

heat transfer - conduction through fibers is negligible

Convection not important except for large volumes of low density

insulation

.

23
[12] Rowley, F. B., Jordan, R. C. , and Lander, R. M. , Thermal Conductivity of

Insulating Materials at Low Mean Temperatures, Refrigerating Engineering (J. of

ASRE) , Vol. 50, No. 6, 541-4, (Dec., 1945).

PURPOSE

An apparatus was built to measure thermal conductivity of common insulating materials at low temperatures

SPECIMEN

a) 0j75 to 1 inch (1.9 to 2.5 cm); b) 1.65-15.7 lbm/ft^ (26 to 251

kg/nr); b) air, atmospheric

APPARATUS

a) guarded hot plate; b) 12 x 12 in (30 cm) sq/ 8 x 8 in (20 cm) sq; c)

vertical

DATA

a) -60 to 90°F (-51 to 32°C); b) Table 1: for 10 materials of varying

density, k vs Tmean ; Figs. 3-10 k vs Tmean at a given density

ANALYSIS

c) Dropping Tmean , drops k with the higher density materials having

the lower percentage drop

24
[13] Wilson, F. C., Evacuated and Gas-filled Insulation Systems, Refrig. Eng.,

pp. 57-60, 102, (Apr. 1957).

PURPOSE

Study effective thermal conductivity in fibrous glass insulation vs species of fill gas, gas pressure, fiber diameter.

SPECIMEN

b) 1,2,9.7,10.9 lb/cu ft (16,32,155,174 kg/m; c) R-12, C02> Ne at

atmospheric, air at 10 Urn Hg to 1 atm (10~3 to 100 kPa); d)

27,150,350,500,600, micro-inches (0.68,4,9,12,15 pm); e) none; f) two

gas mixtures: H2~C02 and R-12-air.

APPARATUS

a) guarded hot plate; b) specimen in thin bags enclosing fill gas, or apparatus in steel vacuum tank

DATA

a) 75-150°C;

b) Tables I-III: k vs fill gas species at three mean temperatures, four

fiber diameters and four densities:

Figure 12 3,4

5

k vs mol.wt. of fill gas

k vs pressure

k vs volume mixture % of CO2 , H2 and of R-12, air

k vs density for various fiber diameters

ANALYSIS

c) to reduce thermal conductivity by choice of fill gas, use any

mol .wt . 50,

k is greater for coarser fibers,

k is at residual level for p _< 0.01 mm of Hg (1 Pa),

k increases less than linearly from value for high-mol.wt. fill gas when

diluted (air),

Optimum density for 150 micro-inch (4 pm) fiber is 2.5 lb/cu ft (40

kg/m3

).

25
[14] Zabawsky, Z., An Improved Guarded Hot Plate Thermal Conductivity Apparatus

with Automatic Controls, ASTM Symposium on Thermal Conductivity Measurements,

STP No. 217, 3-17 (1957).

PURPOSE

To describe an apparatus constructed according to ASTM Standard C177-45

but with additional changes to allow measurement of k within 1% of values

determined by the National Bureau of Standards.

SPECIMEN

a) 0.5 to 1.5 in (13 to 38 mm); b) 9.6, 15.7, and 68.2 kg/m^

APPARATUS

a) guarded hot plate; c) horizontal; d) thermocouples; f) heater to

guard + 0.004°F (0.002°C), cold plate control + 0.05°F (0.03°C),

reproducibility + 0.5%.

DATA

a) 60~110°F (16 to 43°C); b) Fig. 14 k vs T for three fiberglass

materials

26
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBSIR 80-1640

2. Performing Organ. Report No, 3. Publ ication Date February 1981

4. TITLE AND SUBTITLE

Effective Thermal Conductivity of a Glass Fiberblanket

Standard Reference Material

5. AUTHOR(S)

D. R. Smith, J. G. Hust, and L. J. Van Poolen

6. PERFORMING ORGANIZATION (If joint or other than N BS. see instructions) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Department of Energy

Oak Ridge Operation

Oak Ridge, Tennessee 37830

(Under Interagency Agreement DoE No. DE-AI05-780R05965)

10. SUPPLEMENTARY NOTES

J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl iography or literature survey, mention it here)

This paper describes the results of thermal conductivity measurements at

temperatures from; 84 K to 360 K on a glass fiberblanket insulation which

is intended to be a Standard Reference Material (SRM). The measurements

were performed in an atmosphere of dry nitrogen at a pressure near 84 kPa

(630 mm Hg). The results are analyzed and compared to literature data for

similar material. An annotated bibliography of literature sources is

12. included.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Glass fiberblanket; insulation; low temperature; standard reference material;

thermal conductivity.

13.

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