NBSIR 81-1639

A111DS 8,12177

EFFECTIVE THERMAL CONDUCTIVITY OF A GLASS

FIBERBOARD STANDARD REFERENCE MATERIAL

David R. Smith

Jerome G. Hust

Thermophysical Properties Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

-QC

100

. U56

81-1639

1981

February 1981

NBSIR 81-1639

40 *

EFFECTIVE THERMAL CONDUCTIVITY OF A GLASS

FIBERBOARD STANDARD REFERENCE MATERIAL

David R. Smith

Jerome G. Hust

Thermophysical Properties Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

February 1981

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

MATIOMAL BUSBAU

OF 8TAMDA&DS

LIBRARY

MAY 1 3 1981

OlCC . -

' Us

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

CONTENTS

Page

Introduction 1

Apparatus and Specimen Characterization 1

Results . 3

Discussion . . . . 5

References (Annotated Bibliography) . 12

iii

Effective Thermal Conductivity

of a Glass Fiberboard Standard Reference Material

David R. Smith and Jerome G. Hust

This paper* describes the results of thermal conductivity

measurements on NBS SRM 1450 glass fiberboard insulation (1970

lot) at temperatures from 87 K to 340 K. 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

NBS certification data and to literature data for similar material.

An annotated bibliography of literature sources is included.

Key words: Glass fiberboard; insulation; low-temperature ; standard

reference material; thermal conductivity.

Introduction

Previous work on effective thermal conductivity of several lots of glass

fiberboard Standard Reference Material (designated as SRM 1450) has been

reported [l] for specimens in air at local atmospheric pressure and at mean

temperatures of 255 K to 330 K. Results of measurements are reported here for

the 1970 lot of SRM 1450 fiberboard for specimen temperatures covering the

range from 87 K to 340 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 20 cm (8 in) diameter

and 2.6 cm (1.0 in) thickness. They were cut from larger slabs measuring 28 by

30 cm, 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 (0.322 g/cm^ and 0.317 g/cm^). The thickness, Ax, of

each specimen was determined during the conductivity measurement by three

quartz spacer tubes positioned at three equidistant points around the

perimeter; small notches were cut in the edge of each specimen to receive the

spacers. The thickness during measurement was 2.59 cm and the resulting volume

density was 123 kg/m^. No correction for thermal contraction of the quartz

spacers was necessary (less than 0.01 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 100 K to 325 K. with temperature

thermocouple Reference Tables based on IPTS-6S, MBS Monograph 125, March, 1974.

3
differences of about 25 K (gradient approximately 1 deg/mm). Larger gradient

runs (up to AT = 100 K) were taken at some temperatures to search for the

presence of non-conductive heat transfer mechanisms. 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 2Am

» This

area was corrected for thermal expansion (less than 0.7 percent).

The mean thermal conductivity, Tc, was computed according to 3c = ^ TM =

VI Ax

7

-7— 7--——r, where T„ and T.. are the average hoi: and cold side temperatures,

^Am u2 ^ 1 ' '

respectively . The resulting data set of values k, Q, T^» and T 2 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^ (87 K) to the highest

value of T2 (340 K) . This resulted in the values of the parameters, ,

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

that the mechanisms of heat transfer are conductive in nature (as opposed to

direct radiation or convection). Deviations from this condition can he

detected by searching for systematic trends in the deviations of the fitted

data as a function of boundary conditions. The principle variable examined for

such deviations was AT = T2 “T^. It was noted that no trend exists in the

deviations, within experimental scatter, for temperature differences ranging

from 25 K to 100 K.

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

published in Cryogenics.

4
The values of k vs. temperature obtained by means of this technique for

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

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

The fact that the mean values of thermal conductivity, Tc, 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 Tc 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, , and the range over which the

fitted curve is valid. The TCI deviations, (TCI0 bs - TCIca ^ c ) x 100/TCIo bs ,

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 tern polynomial

fit showed systematic deviations from the data at low temperature but the four

terra polynomial exhibits only random deviations.

Discussion

Previous NBS work [1] on the lot of insulation SRM's from which our specimens were taken resulted in certification data given by k = A0 + A^d + A2 T^

where A0 = 0.02052, A^ = 1.303 x 10“^ ^

= 4.015 x 10~10, d = density (kg/m^)

and T = absolute temperature (K) . The differences between the certification

data and our results are shown in Fig. 2 (+)

.

The previous work on this SRM 1450 performed at NBS/Washing ton [1] resulted in a different representation of the fitted curve, with only one temperature

dependent term, while we find it necessary, because of our broad temperature

5
range, to use the four terra polynomial in temperature given earlier. Although

a systematic difference exists (the certification values are larger over most

of the range) between our data and the certification data, the agreement is

within 1.5 percent over the whole range of temperature common to both investigations. Our estimated uncertainty of measurement is about 1 percent. The NBS

certification data is uncertain by about 2 percent.

Other investigators [3-16] have reported the same 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, such

as binder or lubricant content, fiber size or atmospheric pressure actually

present at each laboratory, are not known well enough to permit detailed statements about the agreement or disagreement between results. Comparisons of literature data [1,8,10,12-14,16] to our equation are illustrated in Fig. 3.

Research on SRM 1450 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 and plate emittance will also be examined to further elucidate the nature of the heat transfer mechanisms present.

6
Table 1

Thermal conductivity of fiberglass board (SRM 1450) versus temperature

based on the fitted results of the present investigation.

7
Table 2

4

1 Coefficients of the Least-Squares Fit: k = £ A T

i

i=l

A1 = 0.114622

A2 = 0.149249 x 10" 3

A3 = -0.104388 x 10“ 5

A4 = 0.163799 x 10“8

Range: 87K < T < 340K

8
o

TT CO CM a-ui/MUJ ‘AllAllOnaNOO ivmuiHi

9

TEMPERATURE,

K

Figure

1

Thermal

conductivity

data

for

SRM

1450

glass

fiberboard.

Solid

line

shows

results

of

least

squares

fit

of

thermal

conductvity

integrals,

circles

are

mean

k

values

plotted

at

the

mean

experimental

temperatures

.
I ! % ‘SN011V8A30

UU

oc<K

IUa2

yjH

C

X cO 3 s o o CM CO X o X a CO r—

o c 3 m CO CO w

cm a)

a CD rH CO S-i o M M <d CD CJ X M X H u 3 4J

V_'

x

cO c

co • M CD

t-H T3 CD CD 3 M a s M CO a 4-1 60 O CD CD

CD

X 4-1X 4-) M C a> CD CO X X X CD •H CO O

>> cm o G x •H CD — CO T3 J-i > CO c CD X 03 X CM

J-J r—j CM

CD 60 COX

M TJ T3 o cO C in X Et O ^r o V r—H X X

cO co i—

4-1 tO c2 c CO a CO o G M N 60

CD •H •H „C o U CO X o • X co 3

'O

M 3 4-1 o> CJ> TO X 3 > H P-, T3 m Tf cd Mm C

co

O CD • O

X

U 4-1

X o CO 3 £2 4J 0 J-I 5 3

CM

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O rH

M 3 X

ctf <DM

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60

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10
a-ui/MUi ‘AXIAIJLOnaNOO 1VWH3H1

11

Figure

3

Comparison

of

literature

data

on

glass

fiberboard

specimens

ranging

in

density

from

60

kg/m^

to

184

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 fiberglass boards. 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
[l] Siu, M. C. I., Fibrous Glass Board as a Standard Reference Material for

Thermal Resistance Measurement Systems, in Thermal Insulation Performance,

ASTM STP 718, D. L. McElroy and R. P. Tye , eds., American Society for Testing

and Materials, 1980, pp . 343-360.

PURPOSE

Measurements on over 300 pairs of specimens and statistical analysis of

data. Discussion on use of this material as an SRM.

SPECIMEN

a) 1 inch (25 mm) thick; b) 120 to 160 kg/m“3; c ) air/atraospheric

APPARATUS

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

DATA

a) 255 to 330 K/10 K/cra; d) approximately 0.3% imprecision and 1%

uncertainty.

[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%; f) apparatus operated over the range

approx. 80 to 350°K

14
[3 ] Agrawal, K. N. , Verraa, V. V., An Apparatus for the Study of Heat and Mass

Transfer Properties of Insulating Materials at Low Mean Temperatures, Indian J.

Technology 7(1) , 4-8 (Jan 1969).

PURPOSE

Reports design of an apparatus for studying thermal properties and watervapor transmission characteristics of insulating materials. A standard

sample (NBS) of fiberglass was used to test accuracy of instrument.

SPECIMEN

b) 69 kg/m^ and 84 kg/m^; c) air/atmospheric; h) moisture

absorption

.

APPARATUS

a) Refrigerated room/heat-flow meter; b) 60 cm sq . ; c) vertical;

d) copper-constantan TC; e) heat-flow meter calibrated with hot-plate

apparatus

.

DATA

a) 10°C; b) Table 1: Density, moisture absorption and thermal conductivity of 7 insulations.

For Glass wool (69 kg/m^): k = 0.251 mW/cm.deg at Tm=10°C

Fiberglass (84 kg/m^): k = 0.216 mW/cm.deg at Tm=12°C

15
[4 ] 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 Ib/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

Table 12 3,4,5

6

Figure 12

3

4

5 6,8

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

k vs density for glass wool batts

k vs p for air cell

k vs p vs 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.

16
[5 ] 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

4

6

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.

17
[6] 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-

^ 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.

pLo

k __ = k ————, Lo=inter-fiber distance=TTD/4(l-£)

eff gas gas pLo+ET*

k

eq

k

eff

fib

rad

- 32(1~E)2

= 4aLT

3

/(8

_1

+Lo(2/£o-l)/d) = 4 oL 0 BT

3 m m

DATA

a) 0 to 56°C; b) Figure 2:

6 : 7:

8:

9:

10 : 11 :

12 :

13, 14:

15:

16:

Open-pore two-phase model.

Radiation coefficient, 3, vs porosity, £. kfib vs porosity

8 vs £ for different temperatures.

Structural parameter, a, vs porosity, £. £

g vs £

Radiational conductivity vs specimen

thickness

k vs Tmean for d = 16.4 kg/m^, low ( 10“^ mm Hg)

pressure

k vs pressure. Tm

= 30°C, d = 16.4 and

78.6 kg/m^

k vs Tm

at atmospheric pressure.

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 kgff; d) Conduction in

gas contributes largest part of ke ff in range 15-80 kg/rn^. 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.

18
[7] 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/m3

; c) air, CO2 , R-12; d) 12 x 10~6 ra ; e) none

APPARATUS

a) guarded hot plate; c) horizontal; d) copper-constantan TC's

DATA

a) -15 to +15°C/26 to 66 K/cm

b) Figures 2,3,4:

air: = k2 = k3 =

kl = k2 =

k2 =

CO2

*

R-12:

(33.8

(26.8

(26.3

(23.6

(18.3

( 12.0

vs T, several densities + 0.208t)xl0-3 kCal/m.h. °C, + 0. 145t)xl0-3 + 0. 120t)xl0-3 + 0. 185t)xl0-3 + 0.080t)xl0-3

+ 0. 100t)xl0-3

d^ = 33 kg/m3

d2 - 88 kg/m3

d^ = 120 kg/m3

ANALYSIS

a) At 0°C

k (CO ) k (CO ) k?( R i?)

t-—

7

~ = 0.70, r

- 7 -r = 0.69, --

y

- :- - -v k^(air) k

2 (air) k

2 (air)

0.45

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

at Tm

= 66 °C

.

and kl g

( air ) k lc (air)

k2c ( air > k3c( air >

( 20.8 + 0.060t)xl0-3

(13.0 + 0.l48t)xl0~3

(5.55 + 0.084t)xl0-3

(4.75 + 0.058t)xl0“3

kCalxm*h *°C

kCalxm*h‘°C

kCalxm*h*°C

kCalxm*h*°C

k

2g ~ k 3g

19
[8 ] 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 TC's;

e) measured reference material calibrated at National Physical Laboratory

(England)

DATA

a) -5 to 80°C

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

9B: ke ff vs AT, glass wool

20
[9] 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

micro-inches (0.55,1.12,3.38,12 ym); e) heat felting or phenolic resin

APPARATUS

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

differential TC; 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^:

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 50 10~^ in (130 ym)

.

At low p, higher density not harmful.

Mean free path and average fiber spacing control k.

Optimum density 8 lb/cu ft (130 kg/m^) at vacuum, 4 lb/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,

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

radiation between surfaces.

21
[lO] Codegone , C. , Ferro, V., and Sacchi, A., Studies on Heat Transfer in

Refrigeration (Proc. of HR, Comm. 2, 1966) Pergamon Press, Ltd., Oxford, 23-37

(1966).

Purpose

Thermal insulating material made up of fiberglass was tested at

temperatures to -190°C in order to study convective effects.

SPECIMEN

a) 15 cm radially; b) 75 kg/m2

; c) dry ^/atmospheric ; d) 6 Dm

APPARATUS

a) cylindrical, calorimetric method, guarded; b) 180 cm long x 20 cm diameter/60 cm long; c) horizontal; d) copper constantan thermocouple

THEORY

a) circular isothermal distribution assumed in finding k equation

DATA

a) 0° to -190°C, one gradient from 0° to -190° over 15 cm radially;

b) Table 2 - k vs T, Figure 9 - k vs T, k = 4.196 x 10-2 + 1.973 x 10~^t +

3.719 x 10"8 t 2 [W/m°C]

ANALYSIS

a) results compared to those in a square plate apparatus; b) effect of

convection studied; c) the values in the cylindrical apparatus are 20-40% higher than those in the square plate apparatus due to convection

enhancement of heat flow.

22
[11] Finck, J. L., Mechanism of Heat Flow in Fibrous Materials, J. of Res. of

N.B.S. 5. 973-984 (1930).

PURPOSE

Made a systematic study of thermal conductivities of fibrous materials

showing effects of packing density, fiber arrangement, moisture,

convection and radiation of conduction.

SPECIMEN

a) 1 in. (2.5 cm); b) 0.16 g/cm ; c) air/atraospheric

APPARATUS

a) flat hot plate; b) 8 in (20 cm) sq.; c) vertical

DATA

a) 32°C/30°C/in (12°C/cm); b) all data reduced to value at t = 32°C by

kt = k32 [ 1 + (t - 32)], = 0.0032, as found by averaging over values for

numerous materials; d) 2 %

Table I: k32 vs density for 21 fibers including asbestos (almost all

vegetable fibers);

II: k02 vs density for 3 fibers at 53% Rel . Hum.

Ill: k32 vs density for fiber mixtures

IV: k32 vs fiber arrangement

V: Selected fibers are chosen to study effects of convection and

radiation

Figure 1: k32 vs density

2 : k32 vs density: dry and moisture-conditioned

ANALYSIS

c) For a given fibrous material and a given density, the conductivity may

vary by several hundred per cent, depending entirely on the arrangement of

the fibers. The maximum conductivity is obtained when the fibers are parallel to and the minimum conductivity is obtained when the fibers are perpendicular to the direction of heat flow.

23
[12] 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 (2.5 cm); b) 0.58, 0.78, 1.94, 3.80 lb/ft3 (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, 50°F/in (38°C, ll°C/cm)

Table 1: k vs fill gas; k(air) vs p; % reduction in heat transfer due

to gas substitutions

2: k vs p for air, CO2

> R-12

3: k vs % mixture of (CO2

, R-12) with air

4: k vs T for various gases/densities

5: Calculated Different Modes of Heat Transfer for three

densities, three gases, vs T.

Figure 7: k vs T for glass wool in air, CO2 , R-12 for varying

insulation densities

9: Gas transferred heat vs T for various fill gases

11: 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 CO 2 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

24
[13] Tye, R. P., Measurements of Heat Transmission in Thermal Insulations at

Cryogenic Temperatures Using the Guarded Hot Plate Method, Prog, in Refrig.

Sci . & Techn. Proc . XIII Int’l Conf . of Refrig., Wash., DC, pp. 371-378

(1970).

PURPOSE

Has measured heat transmission in a number of different thermal

insulations, using a guarded hot plate. Looked at influence of vacuum on vermiculite

.

SPECIMEN

a) 25 mm; b) 183.5 kg/m^; c) dry N2/7*10~5 to 760 torr (10~5 to 100 kPa)

APPARATUS

a) guarded hot plate; b) 20 cm diam.; c) horizontal;

d) copper-constantan TC's.

DATA

a) 100 to 300 K/15 to 60 K/in (6 to 24 K/cm)

b) Table 1: Details of 11 different specimens

2: k of vermiculite vs pressure

Figure 1: k of cellular plastic insulations

2: k of various insulation

c) + 3%
[14] Wilkes, G. B., Thermal Conductivity, Expansion and Specific Heat of

Insulators at Extremely Low Temperatures, Refrig. Eng. 52(1), 37-42, 68-72

(July 1946).

PURPOSE

The thermal conductivity of several types of low temperature insulation

has been determined for temperatures ranging from 170°F to -300°F. The

conductance of one type of reflective insulation has been investigated for

the horizontal position, heat flowing upward and downward. The results

for the reflective insulation indicate that the conductance with downward

heat flow varies with the mean temperature while with upward flow it

varies with the temperature difference and is independent of the mean temperature except for very small temperature differences. Three

distinctly different methods of determining the conductance were used in

these tests.

SPECIMEN

a) 1,2 in. (2.5,5 cm); b) 11 Ib/cu ft (176 kg/m^); c) dry air/

atmospheric; f) specific heat, thermal expansion, thermal diffusivity

APPARATUS

a) guarded hot plate; b) 7 in/4 in (18 cm/10 cm) test diameter; c)

horizontal; d) copper-constantan TC ; f) heat power determined by gas

evolution

DATA

a) -111, -16, 119°F/76-316°F/in (-79,-27 ,84°C/17-70°C/cm) ; b) calculated

k for values of actual temperature as compared to Tm

« Table 13

4

6

7 13

14

17

18

Figure

12 ,

k vs T for selected insulating materials

Spec, ht . and thermal diffusivity vs Tm Thermal expansion vs T,m mean k vs mean T

k vs T mean spec, ht . vs T

thermal diffusivity vs T, thermal expansion vs Tm

% change in length vs Tm

m

26
[15] 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/m3

); c) R-12, C02 , Ne

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

27,150,350,500,600, micro inches (0.68,4,9,12,15 ym); e) none;

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

at

f ) two

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 C02 , 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. J> 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-raol.wt.

fill gas when diluted (air)

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

ft (40 kg/m3

)

.

27
[16] 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 4- 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

28
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR 80-1639

2. Performing Organ. Report No 3. Publication Date

February 1981

4. TITLE AND SUBTITLE

. Effective Thermal Conductivity of a Glass Fiberboard

Standard Reference Material

5. AUTHOR(S)

Dr. D. R. Smith and J. G. Hust

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

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

Department of Energy

Oak Ridge Operation

Oak Ridge, TN 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 on NBS SRM 1450 glass fiberboard insulation (1970 lot) at temperatures from

87 K to 340 K. 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 NBS certification data and to literature data for similar

material. An annotated bibliography of literature sources is included.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key

Glass fiberboard; insulation; low-temperature; standard reference

thermal conductivi tv.

words by semicolon s)

material

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