NATIONAL BUREAU OF STANDARDS REPORT

/o, O c

7865

THERMAL CONDUCTIVITY OF TWO FIBERGLASS-REINFORCED

PLASTIC-IMPREGNATED SPECIMEN PANELS

by

Henry E, Robinson and Thomas W. Watson

to the

U#S, Naval Ordnance Laboratory

White Oak

Silver Spring, Maryland

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress,

March 3, 1901, as amended by Congress in Public Law 619, 1950. Those include the development and maintenance of the national standards of measurement and the provision of means

and methods for making measurements consistent with these standards; the determination of

physical constants and properties of materials; the development of methods and instruments

for testing materials, devices, and structures; advisory services to government agencies on

scientific and technical problems; invention and development of devices to serve special needs

of the Government; and the development of standard practices, codes, and specifications. The

work includes basic and applied research, development, engineering, instrumentation, testing,

evaluation, calibration services, and various consultation and information services. Research

projects are also performed for other government agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau’s unique competence is required.

The scope of activities is suggested by the listing of divisions and sections on the inside of

the back cover.

Publications

The results of the Bureau’s research are published either in the Bureau’s own series of

publications or in the journals of professional and scientific societies. The Bureau publishes

three periodicals available from the Government Printing Office: The Journal of Research,

published in four separate sections, presents complete scientific and technical papers; the Technical News Bulletin presents summary and preliminary reports on work in progress; and the

Central Radio Propagation Laboratory Ionospheric Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also

five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks,

Miscellaneous Publications, and Technical Notes.

A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular 460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25),

and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957

($1.50), and Miscellaneous Publication 240, July 1957 to June 1960 (includes Titles of Papers

Published in Outside Journals 1950 to 1959) ($2.25); available from the Superintendent of

Documents, Government Printihg Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1006-30-10642 April 24, 1963 7865

THERMAL CONDUCTIVITY OF TWO FIBERGLASS -REINFORCED

PLASTIC-IMPREGNATED SPECIMEN PANELS

by

H« E# Robinson and T* W* Watson

Heat Transfer Section

Building Research Division

to the

U.S. Naval Ordnance Laboratory

White Oak

Silver Spring, Maryland

IMPORTANT NOTICE NATIONAL BUREAU OF STA

for use within the Government. E and review. For this reason, the whole or in part, is not authoriz Bureau of Standards, Washingtor

the Report has been specifically p

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

; accounting documents intended

ubjected to additional evaluation

listing of this Report, either in Office of the Director, National he Government agency for which

lies for its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL DUREAU OF STANDARDS

THERMAL CONDUCTIVITY OF TWO FIBERGLASS -REINFORCED

PLASTIC-IMPREGNATED SPECIMEN PANELS

by

H. E. Robinson and T. W. Watson

1. INTRODUCTION

A series of comparative tests was initiated by Naval Ordnance

Laboratory to investigate the effect of different testing apparatus and

procedures on the values of thermal conductivity determined for specimens of plastic-impregnated fiber-glass reinforced panels* The test re- sults reported herein were made on two specimens (DER-332 and E-787)

specially prepared by Aerojet General Corporation for testing at Southern

Research Institute, National Bureau of Standards, and Aerojet General

Corporation, in that order. The measurements at NBS were authorized by

NOL Project Order No. P.0. 3-0008 (j/0 958/1819/32050).

2. SPECIMENS

Two different panel materials were submitted for measurement, each

in the form of a pair of specimens each approximately 14 by 14 by 0,5

inch in size. At NBS, each specimen was reduced in size to the central

9 by 9 inch square; the principal faces were not worked in any way.

When received, the pairs of specimens were identified by the numbers

DER-332-A and DER-332-B, and E-787-A and E-787-B. These numbers were

continued on the reduced specimens, and are used for reference in this

report.

None of the reduced specimens was flat to 0.002 inch, nor uniform

in thickness. Measurements of thickness (recorded to 4 figures) were

made on each specimen by micrometer at three locations along each side

of the central 7-inch square, and at the center and four corners of the

central 4-inch square. These measurements are tabulated in Table 1.

As. the tabulation averages show, the average specimen pair thickness over the central 4-inch square was a few mils less than the average

pair thickness at the 7-inch-square trace, at room temperature, for both

pairs. The average departure of the specimen face contours from two

flat planes on both sides indicated by this difference can only be increased by the out-of-flatness, or warp, of the specimens, which may
- 2-

TABLE 1

SPECIMEN THICKNESS DATA

DER-332-A DER-332-B E-787-A E-787-B

(Edges) 0.4828 in* 0.4824 in. 0.4592 In. 0.4826 in,

.4833 .5057 .4638 .4827

.4982 .5061 .4643 .4827

.5020 • 5073 .4636 .4828

.5016 .5079 .4696 .4858

.5072 .5099 .4868 .4927

.5093 .5103 .4998 .4963

.4980 .5090 .4970 .4953

.4922 .5137 .4893 .4956

.4932 .5155 .4813 .4917

.4868 .5142 .4621 .4860

.4833 .5080 .4582 .4834

Avg. 7-in. (.4948) (.5075) (.4746) (.4881)

Avg. for pair at 7-in. (.5012) (.4814)

(Center) .4864 .5077 .4684 .4850

.4934 .5071 .4744 .4902

.4828 .5090 e 464Q .4832

.4856 .5074 .4626 .4808

.4896 .5100 .4725 .4853

Avg.over 4-in. sq e (.4876) (.5082) (.4684) (.4849)

Avg. for pair over 4-in. sq.(.4979) (.4767)

Difference of pair averages .0033 .0047

change when a temperature difference exists face-to-face but could not be

significantly reduced by the pressure exerted on the faces by the apparatus

during tests * At room temperature, the specimens had different apparent

amounts of warp:

DER-332-A:

DER-332-B:

E-787-A:

E-787-B

slightly out-of-flat, more than thickness difference,,

slightly out-of-flat, more than thickness difference,

saddle-shaped warp, out-of-flat >1/16 in. in two directions,

cylindrical warp, out-of-flat 1/16 in. in one direction.
-3-

3. METHOD AND PROCEDURE OF TEST

The thermal conductivity measurements were made in an 8-inch guarded

hot plate apparatus (conforming to ASTM C177) having a 4-inch- square

central metering section* The tests were conducted in a cabinet in air

maintained at within one degree F of the specimen mean temperature; the

exposed edges of the specimens were covered by about 1/2 inch of good

blanket insulation.

Because of the expected low thermal resistance of the principal

specimens, the tests were made using a composite-specimen technique

which avoided need for thermocouples applied to the specimen faces. A

resilient pad was interposed between each face of the specimen and the

adjacent metal hot or cold plate of the apparatus, so that there was on

each side of the hot plate a composite specimen consisting of pad, specimen, pad* The total temperature drop through the composite specimen was

measured by means of permanent thermocouples installed in grooves in the

metal faces of the cold and hot plates, and the test yielded as its result the average thermal resistance of the two composite specimens over

the central 4-inch- square area. By subtracting from the average composite resistance the average thermal resistance of the two pads at the

same mean temperature and total thickness, as determined in a separate

test or tests using the same permanent plate thermocouples, the average

net thermal resistance and conductivity of the principal specimens was

calculated.

Two different kinds of resilient pad were used. The first was 1/8-

inch thick commercial gum rubber (30 to 45 Durometer floating stock,

Fed. Spec. MIL R-880A). In the form of an 8 by 8 by 1/8 inch sheet this

rubber is practically incompressible under the pressure imposed by the

plates of the apparatus (not more than 50 lb/ft2

), but it is resilient

enough to conform to slight irregularities of contacting surfaces.

However, as mentioned in the Discussion later, the rubber pads were not

able to wholly compensate for the variable thickness and warp of the

submitted specimens. For this reason, the tests were repeated using

pads of an open-cell foam material (similar to Scott Paper Company

"Skeletal Structural Industrial Polyurethane Foam") of about 50 pores

per lineal inch and 1/4 inch in uncompressed thickness. As used, the

1/2-inch thickness of the foam pads of each composite specimen was compressed to about 0.07 inch. The average combined thickness of the two

pads in the 4-inch-square metering area was determined by subtracting

from the measured average distance apart of the flat hot and cold plates

the average thickness of the principal specimens in the 4-inch-square

central area as recorded in Table 1. This procedure compensates for

warp of the specimens, and as much as feasible for the variable thickness

of the specimens.
-4-

The thermal resistance of the foam pads, at various thicknesses and

mean temperatures, was determined by a series of tests of the same pads

alone, results of which are presented graphically in Figure 1. The re- sistances corresponding to thicknesses of the pads in the composite

tests were obtained from the appropriate curve, with a slight correction

for actual pad mean temperature (dR/dT = -0.0006 per deg F) 0

4. RESULTS AND DISCUSSION

The results of the measurements are summarized in Table 2. Because

differences are involved, the data are given to four places.

The conductivities obtained for both submitted specimens using the

rubber pads are definitely much lower than those obtained using the foam

pads. The latter results are considered nearly correct.

Apart from the consideration that the conductivities obtained using

rubber pads are of magnitude lower than would be anticipated for materials of this density and composition, there is internal evidence that

these results are erroneously low. Table 2 shows that in the test at

66„8°F of the DER-332 specimens there was apparently a total thickness

difference of 0.0043 inch not accounted for by the principal specimen

and the two rubber pads. It is doubted that resilience of the pads

would have accommodated to reduce the total gap to much less than 0.004

inch* An air gap of this thickness has a thermal resistance of 0.004/

0.187, or 0.021 deg F per (Btu/hr ft2

). Reducing the net principal

specimen resistance given in Table 2 for DER-332 at 66.8°F (0.1728) by

0.021 yields a specimen thermal conductivity of 3 <*27 Btu/hr ft 2 (deg F/in.)

which compares with the value 3®23 obtained with foam pads at 67.1°F.

The values of conductivity of the submitted specimens deduced from the

results of the tests with the rubber pads, by making a correction for

the resistance of the putative air gap as above, are indicated in Table

2 by the values in square brackets. The fair agreement of these corrected values with the corresponding values obtained with the foam pads

suggests that the foam pads compensated reasonably well for the nonuniform thickness and warp of the specimens, and that the results obtained with the foam pads are approximately correct.

Since the foam material had not been used here before for this purpose, the tests on Pyrex 7740 summarized in Table 2 were made for our own

information. The good agreement of the results with the rubber and the

foam pads on these flat and smooth Pyrex specimens, which had approximately the same low thermal resistance as the submitted specimens, indicates the acceptability of the foam material for this use, and also the

general merit of the composite-specimen technique.
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i:. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering) in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside ofthe

front cover. WASHINGTON, 0. C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurement*

Dielectrics. High Voltage.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.

Mass and Scale. Volumetry and Densimetry.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic'Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Stande?d Refer- ence Materials. Applied Analytical Research. Crystal Chemistry.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls.

Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standardsand Research. Dental Research.

Metallurgy. Engineering Metallurgy. Microscopy and Diffraction. Metal Reactions. Metal Physics. Electrolysis

and Metal Deposition.

Inorganic Solids. Engineering Ceramics. Class. Solid State Chemistry. Crystal Growth. Physical Properties.

Crystallography.

Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials.

Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Building Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics, Operations Research.

Data Processing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Far Ultraviolet Physics. Solid State Physics. Electron

Physics. Atomic Physics. Plasma Spectroscopy.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation.

Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Elementary Processes. Mass Spectrometry. Photochemistry and Radiation Chemistry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering Laboratory. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical Services.

CENTRAL RADIO PROPAGATION LABORATORY

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical

Soundings Research. t

. Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Fre-

, quency Utilization. Modulation Research. Antenna Research. Radiodetermination.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. High Latitude Ionosphere

Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

RADIO STANDARDS LABORATORY

Radio Physics. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency and Time-Interval

Standards. Radio Plasma. Millimetei^Wave Research.

Circuit Standards. High Frequency Electrical Standards. High Frequency Calibration Services. High Frequency

Impedance Standards. Microwave Calibration Services. Microwave Circuit Standards. Low Frequency Calibration

Services.

USCOMM-NBS-DC