Reference

NBS

Publications

NBSIR 82-1664

NAT'L INST. OF STAND & TECH

AlllDt. 037314

i ncmvIAL CONDUCTIVITY OF A

POLYURETHANE FOAM FROM 95 K to

340 K

L. L. Sparks

National Bureau of Standards

U.S. Department of Commerce

Boulder, Colorado 80303

March 1982

f

-QC

100

, U56

82-1664

1982

NBSIR 82-1664

NATIONAL BURBAL

Of iTANDABLS

LIBRARY MAY 17 1982

THERMAL CONDUCTIVITY OF A

POLYURETHANE FOAM FROM 95 K to

340 K

L. L. Sparks

Thermophysical Properties Division

National Engineering Laboratory

National Bureau of Standards

U,S. Department of Commerce

Boulder, Colorado 80303

March 1982

Prepared for Gas Research Institute 8600 West Bryn Mawr Avenue

Chicago, Illinois 60631

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler Director
>La liui tA&h
Thermal Conductivity of a Polyurethane Foam From 95 K to 340 K*

L. L. Sparks

Thermophysical Properties Division

National Bureau of Standards

Boulder, CO 80303

Values of thermal conductivity for a 32 kg/m^, CClgF blown polyurethane foam are presented in the temperature range from 95 to 340 K. These data were obtained using a guarded-hot-pl ate apparatus (ASTM C 177). The apparent conductivity is discussed in terms

of contributions from radiation and solid and gas conduction. Heat transfer via gas convection is not significant when the cell diameters are less than approximate! y 3 mm; cell

dimensions of the thermal conductivity specimen are on the order of 0.5 mm.

Key words: convection; foam; gas conduction; guarded-hot-plate; insulation; low

temperature; radiation; solid conduction; thermal conductivity.

1. INTRODUCTION

Safe and economical storage, transportation , and use of cryogenic fluids depend to a large extent

on materials used in construction of associated equipment. Thermal insulation and insulation systems

are critical parts of essentially all equipment which must be used at low temperatures. Generally,

the particular application dictates the generic type of thermal insulation or, at least, reduces the

number of candidates. Some of the widely used types of insulation and concomitant thermal conductivity ranges are shown in figure 1. As seen in this figure, the evacuated insulations are the most

thermally efficient. Most large-scale needs, however, preclude vacuum insulation on the grounds of cost and durability. The three classes of unevacuated insulation are reasonably competitive in thermal effectiveness at low temperatures; all are used, for instance, in large liquefied natural gas (LNG) and liquefied petroleum gas (LPG) storage tanks and tanker ships. The high strength-to-wei ght

ratio of expanded plastics (foams), ~8 kPa/kg/rrr^ compared to ~50 for aluminum alloys and ~25 for

stainless steels, allows these insulations to be self supporting and to lend structural support to the

system. Foam insulations are found in most recent LNG/LPG-oriented construction.

The particular material to be discussed below is a closed cell, rigid polyurethane (PU) foam of

nominal density 32 kg/m^ (2 lb/ft^). A foam is a composite consisting of a skeleton of solid materials and voids filled with various gases. The term "closed cell" is used to describe materials in which the voids form discrete chambers. A foam may be considered rigid when it is used below the

glass transition temperature, Tg. This transition is of the second order and is characterized by a change in the specific heat of the resin. The transition occurs between 400 and 485 K for most PU resins. Polyurethane is a thermosetting material as opposed to a thermoplastic material (polystyrene

*This work was supported by the Gas Research Institute, 8600 West Bryn Mawr Avenue, Chicago, IL 60631.

1
is a thermoplastic material, and thus softens when heated). Thermosetting materials do not soften

significantly at elevated temperatures , but rather decompose directly.

A property of primary importance in thermal insulations is, of course, thermal conductivity (as

applied to cellular composites, the term apparent thermal conductivity is more correct since radiative

and convective components are included along with the true conductive modes of heat transfer). Heat

is transferred through foams via four mechanisms: ( 1 ) gas conduction, Qg , ( 2 ) solid conduction, Q s , (3) radiation, Q r , and (4) convection, Qc

. The total heat flow, Qj, via the four parallel modes is normally assumed to be additive

Q

+

's q + T

( 1 )

The dominant mode of heat transfer in an insulating foam is gas conduction until the temperature

becomes low enough to liquefy the cellular gas. Solid conduction through the resin structure is small

but not negligible (the solid conduction is a function of foam density). Radiation is similarly a small, but not negligible, component. Convective heat transfer is negligible for snal 1 -cel 1 foams

(cell diameter 3 to 4 mm) ( Skochdopol e , 1961); however, this component becomes critically important

for cracked foams and slab installations where vertical cracks allow natural convection.

The effect of aging and gas permeability on the thermal conductivity must be considered when

foams are used in facilities with long lifetimes. As mentioned above, the total heat transfer through

a foam is very dependent upon the cellular gas content. The gas content is, in turn, dependent on age, permeabil ity , and how the foam is shielded from the atmosphere. The rates of diffusion of gases

into and out of PU foams are indicated in table 1. As seen in this table, PIJ would tend to lose a heavy fluorocarbon gas, such as CCI 3 F, very slowly but would absorb air approximatel y 15 times as rapidly. If unprotected, air will diffuse into PU foam until the partial pressure of air is equal

inside and out; this, combined with the slower loss of heavier fluorocarbon fill gases will result in

a net positive pressure. Eventually the equilibrium gas content will be air at ambient pressure.

Table 1. Permeability of gases through PU films (Scott and Roff, 1971)

n u • i

- 4. i n-15 cm3 gas • mm Permeability, 10 -——

s • cm3 . Pa

Ga s Polyester Polyether

CClgF 2.2

N

2 20.3 36.8

°

2 80.3 112 to 360

c °2 30.0 1050 to 3000

Ai r 32.3

2
2. APPARATUS

T he apparatus used to make the thermal conductivity (k) measurements is shown schematically in figures 2 and 3. The path of the cooling fluid is shown in figure 2 and the details of the specimen

configuration are shown in figure 3. This type of system is commonly known as a guarded-hot-plate and

is described in the American Society for Testing and Materials Standard C 177 (ASTM, 1978). This

method allows an absolute determination of k and is considered to be the most accurate method available for insulations. The particular apparatus used to make the k measurements reported here is described in detail by Smith, Hust, and Van Poolen (1981); a very brief description is included below.

"he basic operation of this type of apparatus involves supplying a measured amount of power, Q,

from the main heater plate to the two specimens and measuring the resulting steady-state temperature

difference. The thermal conductivity is then given by

k AX _Q

2A ‘ aT ( 2 )

where aX is the sample thickness, A the area of the metered section of the main heater plate, and aT

is the steady-state mean temperature difference across the specimens. The absolute temperatures and temperature differences are measured with type K thermocouples.

The accuracy of the k results is dependent on the accuracy of measurement of the parameters shown

in eq (2) and on establishment of unidirectional (vertical in this case) heat flow in the metered area

of the specimens. The inner-guard heater plate is controlled at the temperature of the main heater in order to minimize radial heat flow in the metered area. Somers and Cyphers (1951) and ASTM C 177 indicate that when the diameter-to-thickness ratio of a specimen is greater than 4, the errors in k due to edge losses should be less than 1%. The metered diameter of the foam specimens was 10.2 cm and

the thickness was 2.54 cm.

The most critical and difficult parameters to determine are the specimen temperature differences

(aT); aT averaged 10 K for the PU foam specimens. The correctness of aT measurements depends on

pi ate-to-specimen thermal contact, on unidirectional heat flow, and on thermocouple calibration and

referencing sources of error. The diverse materials which can be tested in this type of system cause

a wide range of pi ate-to-specimen contact situations. Tye and Spinney (1976) found that embedding the

thermocouple wires in the specimen, as opposed to the measuring plates, resulted in higher calculated

conductivities. This effect is due to better specimen-to-thermocouple contact which results in smaller

measured aT and larger k (eq (2)). They also found that the effect of thermocouple placement was dependent on the conductivity of the specimens. As the conductivity of the specimen increases, the

relative effect of an air gap in the specimen-to-pl ate interface becomes larger.

Thermocouple placement used in obtaining the data reported below consisted of cementing the wires

into machined grooves in the measuring plates (plates adjacent to the specimens shown in figure 3) so that the top of the wires were flush with the plate surfaces. The plate emissivity was 0.82.

3
The accuracy of measurements made with this system on fiberglass and fiberboard reference materials is discussed by Smith, Hust, and Van Poolen (1981). In a qualitative sense the plate-to-specimen

contact should be similar for low density foams and the fiberous materials tested by Smith. Rased on the percentage errors given by Smith for each parameter in eq (2) and the magnitude of these parameters for the PU foam experiments, uncertainties in the PU foam data are estimated to be D.2 mW/m*K

random and 0.4 mW/m*K systematic near room temperature; near 80 K the random and systematic components

are 0.1 mW/m-K.

3. MATERIAL

The material tested in this study is a nominal 32 kg/m^ (2 lb/ft^) polyurethane foam (PU) designated as GM30. Our supply of this material was obtained from the NBS Office of Standard Reference

Materials (OSRM), Washington, DC. The OSRM distributed this and other expanded plastics for the Products Research Committee (1980). These materials were commercially produced and designated by OSRM as General Materials. Our bulk supply of GM30 was in the form of a 0.1 x 1.2 x 1.8 m slab. The thermal

conductivity tests were conducted on specimens taken from the circular area indicated in figure 4. The chemical formula for the PU resin in GM30 is CiQ. 47 Hn. 99 O 2 . 38 N, the molecular weight is 189.71,

and the composition by weight is {%) C, 66.2; H, 6.3; 0, 20.2; and N, 7.4 (Products Research Committee, 1980). The orientation of the elongated cell axis for the material used in the physical properties tests was determined optically from statistical evaluation of microphotographs. The ratios of

cell height to cell width for the principal orthogonal planes of the test specimens were: x/y = 1.33 ± 0.24, z/x = 1.02 ± 0.18, z/y = 1.40 ± 0.26. The ± values represent estimates of one standard deviation. The cell orientation relative to the orthogonal axes of the bulk slab are shown

in figure 5. The average intercepted cell cross sectional areas in the principal orthogonal planes were found using the method described by Schael (1967) and are shown in table 2.

Table 2. Average intercepted cell area for two specimens of PU, 32 kg/m^ foam

Specimen XY plane XZ plane YZ plane

GM30-2 1.27xl0~

3 cm'Vcell 1 . 21 xl 0’ 3 cm

3 /cell 1.25x10

3 cm'Vcell

GM30-3 1 . 02 xl 0 -3

1.32xl0"

3 l.llxlO

-3

The cellular surface to volume ratios for the specimens listed in table 2 are 67.7 and 69.6 cm 1

for specimens GM30-2 and GM30-3 respecti vely.

The composition of the gas in the foam cells, table 3, was determined by mass spectrometry at the

beginning of the thermal conductivity tests.

4
Table 3. Gas content of GM30, PU foam as determined using mass spectrometry

Gas Mole %

CC1 3

F 71.2

No 6.1

°2 21.8

A 0.5

COo 0.3

CO 0.1

4. EXPERIMENTAL RESULTS

Thermal conductivity as a function of temperature, for GM30 PU foam, is shown in table 4 and figure 6. These data were determined over a period of 18 days in the guarded-hot-plate system described

earlier. The numbers given in table 4 represent averages of 3 or more determinations of k(T); the

determinations were separated by a minimum of 15 minutes. Each determination is plotted in figure 6,

but the resolution is such that, in every case, the set appears as a single point.

Table 4. Average thermal conductivity as a function of

average temperature for a 32 kg/m^ PU foam

T

(K)

k (mW/m* K)

1—^

k (mW/m»K)

95.10 11.4 256.76 22.6

106.89 13.0 258.17 22.8

120.39 14.6 264.67 21.6

132.04 15.8 270.65 20.4

153.89 18.2 274.67 20.1

169.54 19.9 275.74 19.9

175.29 20.7 280.78 20.0

185.78 21.7 284.90 20.5

202.20 23.1 290.79 21.2

214.63 23.8 297.00 21.6

216.82 23.8 297.95 21.8

220.54 23.9 301.97 22.2

239.67 23.8 318.03 24.5

239.91 23.8 332.38 26.2

248.97 23.6 332.94 26.0

340.22 27.8

The sequence of k determinations was not in order of increasing or decreasing temperatures, e.g.,

one determination might be made at an average specimen temperature (T) of 120 K while the next determination might be made at T = 280 K.

The specimen environment throughout the 18 day testing period was dry nitrogen gas. The gas sur- rounding the specimen was maintained at a slight positive pressure of 260 to 660 Pa (2 to 5 mm Hg)

relative to atmospheric pressure.

5
5. DISCUSSION

As mentioned earlier, heat is conducted through a foamed material via solid and gaseous conduction, by radiation, and by convection. The cell size of the PU foam tested here is too small to allow

natural convection to contribute to the total heat flow ( Skochdopol e , 1961).

The published thermal conductivity data for nominal 32 kg/m^ PU foams at low temperatures are shown in figure 7. A strict quantative analysis of the contribution of each of the three modes of

heat transfer is not possible for the literature data because insufficient information is available.

It is possible, however, to establish in general terms that gas conduction is the principal mode and

that the NBS data reflect the expected conductivity based on the known gas content.

Radiant heat flow through foam insulators is due to transmission and absorption and reradiation.

Resins used for making foams are partially transparent in the 2 to 30 ym range of wavelengths

(Skochdopole, 1961). Sections associated with thermal insulations are normally optically thick

(thickness >> photon mean free path), however, so that direct transmission will be small. The effective Q r is expected to be proportional to t 3 and for nominal 32 kg/m^ PU foams at ambient temperature is equivalent to k r ~ 4 mW/(m-K).

Solid conduction takes place through the cell walls and membranes of the foam. Since PU resins

are made up of disordered ( noncrystall i ne) materials, there is little lattice conduction at low tem- peratures and the conductivity is nearly a linearly decreasing function of temperature. The heat con- ducted by the solid phase can be estimated by

V k

s ss

(3)

where V

s is the relative volume of resin in the foam and k ss is the thermal conductivity of the non- expanded polymer. Using this and k (ambient temp.) = 133 mW/(m-K) (Nadeau, Waszeciak, and Sayigh,

1967), k

s = 4 mW/(m»K), since the resin only occupies approximatel y 3% of the volume of a 32 kg/m3

(2 lb/ff3) foam. This contribution must be further , reduced by a steric factor (Hammond, 1968), i.e.,

the portion of the solid that is perpendicul ar to the direction of heat flow cannot contribute directly to the conduction. This factor depends on the orientation of the cells relative to the direction

of heat flow and is on the order of 0.66 to 1 .

The remaining mode for heat transfer is conduction in the gas occupying the foam cells. As will

be shown below, this is the largest component. Figure 8 indicates the conductivity of the gases typically found in an insulating foam; a combination of CCI 3 F, O2 , and N? was present in the foam tested

here (table 3). When a mixture of gases is present, kg can be estimated by using

n

k = k . . = Vx.k.

g mixture i i i = l

(4)

6
where thermal conductivities of the individual species are given by k-j , X-j represents the correspondi ng mole fraction, and n is the number of species present. A computation of kg at ambient temperature using the gas composition given in table 3, yields kg = 12.9 mW/(m-K).

It is not rigorously correct to add the conductivities due to the three modes of heat transport

(the heat transfer modes are not independent of one another). Results obtained using this approach

have, however, been found to approximate k of rigid polyurethane foams (e.g., Ball, Hurd, and Walker,

1970, and Levy, 1966).

k T= k +

g

k +

r

( 5 )

If one uses eq (5) and the values of k

g

, k s , and k r obtained above, kj = 20.9 mW/(m-K) at 290 K. The

experimental value from figure 6 is 21.1 mW/(m*K). This close agreement tends to verify the composition of gases in the NBS specimen as determined via mass spectrometer.

As temperature decreases, the contribution of radiation decreases as T^ and the contribution of

solid conduction decreases as T. The contribution due to gas conduction, however, is a complex function of temperature and composition. Figure 9 illustrates the conductivity of three gas mixtures as a function of temperature. The shape of the 33, 40, and 47 mole percent CCI 3

F data are similar to that seen in figure 7 for the total, apparent conductivity of nominal 32 kg/m^ PU foams. The variability in the PU data of different experimenters, shown in figure 7, may be attributed to different

gas content at the time of measurement (smaller differences no doubt also occur due to experimental

errors'!. These differences cannot be quantitatively analyzed since specific gas contents are not known for specimens used by other experimenters.

The heat transfer observed in a practical application of PU foam insulation is approximated by

the summation of the integrals of the modes of conduction. The integral approach is necessary since

kj is a non-linear function of temperature and is dependent on the temperature distribution through

the thickness of the foam. As mentioned above, Q r and Q s are small and can be approximated by simple

functions of T. To the first order, the heat flow due to these modes is Ak s AT and k rAT, where A is a constant containing the steric factor and the volume percent resin. These relationships do not account for the fact that solid conduction will be increased slightly when the cell gas condenses or that the gas does absorb radiant energy and this absorption changes with temperature. The gas conduction component, on the other hand, must be divided into temperature zones due to the phase changes

involved. While both CCI 3

F (or other fill gas) remains in the vapor phase a mixture of air and fill

g as must be considered so that k

9

f

T HI

= I k . . dT where T J mixture

T

1

represents the temperature where the fill

gas has essentially all condensed leaving only air in the cells. This temperature is seen to be at approximately 220 K in figure 9. The variation in experimental data shown in figure 7 is also seen to

decrease at about this temperature. This would be expected since the conductivity below this temperature is primarily due to air. At temperatures below Tj , but higher than the air condensing

7
r

Tl temperature (T 0 ), k = J k . dT. When T < T„ , the foam is in a cryopunped state so that

L. Q T air L. t

2 ky = k

s + k r and, since k r

is small, ky ~ k

s

.

This temperature-zone behavior of the gas conduction can be qualitatively illustrated by considering an aged CCI 3

F blown PU foam with one face at 19 K (-425°F) and the other at 300 K (80°F).

Beginning at the 300 K face, gas conduction will be due to the mixture of air and CCI 3 F. The conductivities of several possible mixtures are shown in figure 10. If the mixture is assumed to be 50 mole

percent air and 50 mole percent CCI 3 F, the conductivity will decrease along this constant composition

line until the temperature is reached where CCI 3

F begins to condense. The actual temperature at which

this occurs depends on the partial pressure of the CCI 3

F in the cells. This corresponds to the 278 K inflection in the thermal conductivity of the NBS PU specimen (figs. 5 and 7) and the kg inflection

shown between 275 and 295 K in figure 9. As the temperature is lowered, the mole fraction of CCI 3

F gas

will decrease until essentially only gaseous air is present. This decreasing CCI 3F gas content causes

the observed conductivity to have a negative slope in the range 230 < T 280 K. The second regime of

gas conduction is encountered as the distance to the cold wall is decreased. The gas conduction here

is entirely due to air and decreases smoothly until the components of air begin to condense. The

third regime begins at this temperature. The cellular-gas pressure continues to decrease as the cold

wall is approached and air condenses. The gas conductivity decreases, as would be expected from the

conductivity of air shown in figure 8 . At ~50 K, the pressure in the cells will be approximately 133

Pa (1 mm Hg) and the mean free path of the gas molecules will approximate the cell diameter. Under

these conditions, kg will be a function of pressure. Pressure within the cells and the concomitant

gas conduction continue to decrease as the cold wall is approached. Solid conduction and radiation

remain as the principal modes of heat transfer in the very low (cryopumped) temperature section of the

foam.

6 . CONCLUSIONS

The effective or apparent thermal conductivity of a rigid, fluorocarbon blown foam is strongly

dependent upon the composition of gas in the foam cells. For temperatures encountered in LNG/LPG

installations a complex, double inflected conductivity exists. The observed insulation quality, or conductivity, will reflect the changing gas characteristics as the temperature changes in the body of

the foam. It appears that the effective conductivity can be modeled well enough to allow users and

producers of PU foam to base designs on density and measured gas content.

7. REFERENCES

ASTM (1978). Standard C 177, Steady-state thermal transmission properties by means of the guarded hot plate, Part 18, Annual Book of Standards , American Society for Testing and Materials,

Phi 1 adel phi a , Pennsylvania.

Ball, G. W. , Hurd, R. , and Walker, M. G. (1970). The thermal conductivity of rigid urethane foams,

J. Cell. Plast. 6 , 66-78.
Glaser, P. E. , Black, I. A., Lindstrom, R. S. , Ruccia, F. E. , and Wechsler, A. E. (1967). Thermal

insulation systems, a survey, NASA Spec. Pub. SP-5D27.

Hannond, M. B. , Jr. (1968). An analytical model for determining the thermal conductivity of closedcell foam insulation, AIAA 3rd Thernophysics Conf. Los Angeles, California, 1968, paper 68-766.

Levy, M. M. (1966). Moisture vapor transmission and its effect on thermal efficiency of foam plastics,

J. Cell. Plast. 2, 37-45.

Nadeau, H. G. , Waszeciak, P. H. , and Sayigh, A. A. R. ( 1967). A method for determination of the cellular gas content of rigid urethane foams and its relationship to thermoconductivity, Cell. Plast.

Proc., Nat. Acad, of Sci., NRC Pub. 1462, 109-122.

Ratten, G. A. and Skochdopole, R. E. (1962). Envi ronmental factors in thermal conductivity of plastic

foams, Mod. Plast. (39, 149-191.

Products Research Committee (1980). Material Bank Compendium of Fire Property Data, J. W. Lyons,

Chairman, National Bureau of Standards, Washington, DC.

Schael , G. W. (1967). Characterization of the structure of cellular plastics, J. Appl . Poly. Sci. 11 , 2131-2142.

Schroeder, C. J. (1973). Insulation commonality assessment (Phase I), Rockwell International Space

Division Report SD72-SA-0157-2.

Scott, J. R. and Roff, W. J. (1971). Handbook of Common Polymers , Batterfield and Co., Ltd., London.

Skochdopole, R. E. (1961). The thermal conductivity of foamed plastics, Chem. Eng. Prog. 5(7, 55-59.

Smith, D. R. , Hust, J. G. , and Van Poolen, L. J. (1981). A guarded-hot-plate apparatus for measuring

effective thermal conductivity of insulations between 80 K and 360 K, Nat. Bur. of Stand. (U.S.),

NBSIR 81-1657.

Somers, E. V. and Cyphers, J. A. (1951). Analysis of errors in measuring thermal conductivity of

insulating materials, Rev. Sci. Instrum. _22, 583-586.

Stephan Chemical Co. (1978). Stepanfoam BX-250A: typical physical properties. Technical Information

Bulletin, Urethane Dept., Northfield, Illinois.

Touloukian, Y. S. , Liley, P. E. , and Saxena, S. C. (1970). Thermal Conductivity: Nonmetallic Liquids

and Gases, Thermophysical Properties of Matter , IFI/Plenum, New York.

Tye, R. P. <(1968). The thermal conductivity of two thermal insulating materials, Dynatech Report 798,

Dynatech Corp., Cambridge, Massachusetts.

Tye, R. P. (1971). Measurements of heat transmission in thermal insulations at cryogenic temperatures

using the guarded hot plate method, Proceedings of the Int. Inst, of Ref., Washington, DC, 1971.

Tye, R. P. and Spinney, S. C. (1976). Thermal conductivity of concrete: measurement problems and

effect of moisture, Bull. Int. Froid, Annexe 1976-2, 119-127.

9
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10
Figure 2. Schematic of the guarded-hot-pl ate thermal conductivity apparatus.

A, vacuum insulated transfer tube; B, bottom cold plate; C, vacuum

insulated transfer tube; D, flex tubing; E, top cold plate; F,

transfer tube; G, shroud cooling tubes; H, throttle valve.

11
ENVIRONMENTAL CHAMBER

LIQUID COOLED SHROUD

OUTER GUARD

TOP COLD PLATE

OFFSET INSULATION

TOP AUXILIARY HEATER PLATE

O

t-<

D

00

SPECIMEN

O

I-<

_iD

COZ

INNER

GUARD MAIN HEATER PLATE INNER

GUARD

HEATER

PLATE

(METERED SECTION) HEATER

PLATE

O

I-<

_iD

COZ

SPECIMEN

Z

o

D

00

BOTTOM AUXILIARY HEATER PLATE

OFFSET INSULATION

BOTTOM COLD PLATE

TTTA \ \\ \\ \\ \\ \\ \\ \\ \V\W\VV~

BASE

Figure 3. Schematic of guarded-hot-pl ate specimen configuration and

envi ronmental chamber.

12
13

Figure

4.

Bulk

supply

of

32

kg/m

,

PU

foam

designated

GM30.

The

thermal

conductivity

specimens

were

taken

from

the

circul

ar-shaded

area.
14

Figure

5.

Cell

shape

and

orientation

relative

to

the

pri

nci

pal

-orthogonal

axes

of

the

bulk

supply

of

GM30.

The

connected

short

straight

lines

do

not

represent

actual

cell

boundaries

but

are

rather

artifacts

of

the

method.
o *m US<m

UJ&S

ujH

15

Figure

6.

Thermal

conductivity,

mW/(m.K),

versus

temperature,

K,

for

the

32

kg/rn,

PU

foam

studied

at

NBS.

The

cellular

gas

content

at

the

time

of

measurement

was

approximately

71

mole %

CClgF, 6

mole %
(M-ui)/mw ‘AllAllOnQNOO 1VINU3HJ.

16

Figure

7.

Thermal

conductivity,

mW/(m*K),

versus

temperature,

K,

for

five

nominal

32

kg/m5

,

PU

foams:

O,

Stephan

Chemical

Co.

(1978);

X,

Tye

(1968);

a,

Tye

(1971);

,

Schroeder

(1973);

•,

NBS

(this

report).
THERMAL

CONDUCTIVITY,

mW/(m-K)

25

10

100 200 300

TEMPERATURE, K

Figure 8. Thermal conductivity, mW/(m»K), as a function of temperature, K, for

commonly used fill gases (Touloukian, Liley, and Saxena, 1970).

17
(M UI)/MU1 ‘AllAllOnaNOO IVWaHHl

18

Figure

9.

Computed

thermal

conductivity,

mW/(m*K),

as

a

function

of

temperature

, K,

air

and

mixtures

of

air

and

CCI3

F

at

293 K

(Patten

and

Skochdopole,

1962).
19

Figure

10.

Thermal

conductivity,

mW/(m*K),

as

a

function

of

temperature

,

for

mixtures

of

CCI3

F

and

air

(Hammond,

1968).
NBS-1 14A (REV, 2-80

U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO. NBSIR 82-1664 March 1982

4. TITLE AND SUBTITLE

Thermal Conductivity of a Polyurethane Foam From 95 K to 340 K

5. AUTHOR(S)

L. L. Sparks

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)

Gas Research Institute

8600 West Bryn Mawr Avenue

Chicago, IL 60631

10. SUPPLEMENTARY NOTES

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

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

bibliography or literature survey, mention it here)

Values of thermal conductivity for a 32 kg/m^, CCI 3

F blown polyurethane

foam are presented in the temperature range from 95 to 340 K. These data were

obtained using a guarded-hot-pl ate apparatus (ASTM C 177). The apparent conductivity is discussed in terms of contributions from radiation and solid and gas

conduction. Heat transfer via gas convection is not significant when the cell

diameters are less than approximately 3 mm; cell dimensions of the thermal conductivity specimen are on the order of 0.5 mm.

12. KEY WORDS (Six to twelve entries; alphabetical order; capi ta I i ze only proper names; and separate key words by semicolons)

convection; foam; gas conduction; guarded-hot-plate; insulation; low temperature;

radiation; solid conduction; thermal conductivity.

13. AVAILABILITY

25 Unl imited (m For Official Distribution. Do Not Release to NTIS

) Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

[X] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

2?

15. Price $4.00

-M U.S. GOVERNMENT PRINTING OFFICE: 1982—577-847/153 Region No. 8