NISTIR 88-3861

Room-Temperature Thermal

Resistance Measurements of

New and Existing Materials

for Shipboard Air Duct

Systems

Robert R. Zarr and Thomas A. Somers

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards)

National Engineering Laboratory

Center for Building Technology

Gaithersburg, Maryland 20899

October 1988

Prepared for: Department of the Navy

David Taylor Naval Ship Research and Development Center

Bethesda, Maryland 20084

75 Y««n Sttmuiatirg America * ProQt»m

1913- >949

NISTIR 88-3861

Room-Temperature Thermal

Resistance Measurements of

New and Existing Materials

for Shipboard Air Duct

Systems

Robert R. Zarr and Thomas A. Somers

U.S. DEPARTMENT OF COMMERCE

National Institute of Standards and Technology

(Formerly National Bureau of Standards)

National Engineering Laboratory

Center for Building Technology

Gaithersburg, Maryland 20899

October 1988

National Bureau of Standards became the

National Institute of Standards and Technology

on August 23, 1988, when the Omnibus Trade and

Competitiveness Act was signed. NIST retains

all NBS functions. Its new programs will encourage

improved use of technology by U.S. industry.

Prepared for: Department of the Navy

David Taylor Naval Ship Research and Development Center

Bethesda, Maryland 20084

U.S. DEPARTMENT OF COMMERCE

C. William Verity, Secretary

NATIONAL INSTITUTE OF STANDARDS

AND TECHNOLOGY

Ernest Ambler, Director

Room-Temperature Thermal Resistance Measurements

of New and Existing Materials

for Shipboard Air Duct Systems

Robert R. Zarr and Thomas A. Somers

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Gaithersburg, Maryland 20899

Thermal resistance measurements of conventional and composite material

insulation for shipboard air duct systems are described. Conventional

shipboard air ducts are constructed of metal walls insulated externally

with fibrous-glass board. Composite materials are being considered as

replacements for these duct walls. Thermal measurements were conducted

using the National Bureau of Standards 1 -metre Guarded Hot Plate at a mean

temperature of 23.9°C (75°F). Measurements of the fibrous - glass board

specimens were within 3% of certified values of NBS SRM 1450a, fibrousglass board. Measurements of two aramid- fiber honeycomb specimens were

approximately one-half the thermal resistance of the fibrous-glass board

specimens.

Key words: aramid fiber; composite materials; fibrous-glass insulation;

guarded hoot plate; polyimide foam; thermal resistance

l
.

.

'

,
1 INTRODUCTION

Composite materials are being considered as replacement materials for

shipboard air duct systems. Currently, shipboard ducts utilize a heavy

metal wall construction insulated externally with fibrous-glass board

insulation. Thermal resistance measurements of these materials, both

existing and new, are necessary to determine the thermal performance of

the duct wall. The thermal resistance of two specimens from existing

shipboard ducts and three specimens of composite materials were measured

using the National Bureau of Standards (NBS) 1 -metre Guarded Hot Plate

(GHP) . This report details results of thermal measurements for the first

set of five insulation specimens provided by the U.S. Navy.

2 NBS 1 -METRE GUARDED HOT PLATE

The NBS 1-m Guarded Hot Plate consists of three temperature-controlled

plates of anodized aluminum, each 1.016 m (40 in.) in diameter. The

temperature-controlled plates are housed within a large, six-sided

rectangular environmental chamber, 1.4 by 1.4 by 1.6 m high (4.6 x 4.6 x

5.3 ft). Two sets of double-doors, both front and back, allow access to

the apparatus plates. Air is conditioned and circulated within the

chamber by a small heat exchanger consisting of a chilled-water coil,

electric-resistance heater and blower. The apparatus is illustrated in

Figure 1

A schematic diagram illustrating the principle of measurement for the

NBS 1-m Guarded Hot Plate is shown in Figure 2. In a two-sided mode of

operation, two similar homogeneous specimens are brought into intimate

thermal contact with the plates. A steady temperature difference (AT) is

produced across the specimens, until a steady heat flow (Q) is achieved

through the specimens. A differential thermopile across the gap is used

to null the gap temperature difference, minimizing lateral heat flow

(Qgap ) at the gap. The net effect of the specimen edge losses (Qedge ) are

minimized by the large specimen diameter to thickness ratio and by

controlling the ambient air temperature the same as the mean specimen

temperature

The NBS 1-m Guarded Hot Plate is operated in a one-sided mode of

operation when only one test specimen is available. In a one-sided

configuration, a steady temperature difference is maintained across the

specimen using the hot plate and one cold plate. Another insulating

material, known as the backflow specimen, is inserted between the hot

plate and the second cold plate. The second cold plate is maintained at

the same temperature as the hot plate thereby reducing the heat flow (Qb ) through the backflow specimen to about zero. The remainder of the test

proceeds exactly as the two-sided test described above. Further

information on the design and operation of the NBS 1-m GHP is available in

references [2] and [3].

1
3

SPECIMEN DESCRIPTION

A total of five specimens was received from David Taylor Naval Ship

Research And Development Center. Specimen composition and physical

dimensions are listed in Table 1.

Table 1„ Specimen identification and physical dimensions

Thickness Area

Sample Specimen (mm) (in) (mm x mm) (in x in)

01 Galvanized-steel panel insulated

with fibrous-glass board

02 Aluminum panel insulated

with fibrous-glass board

03 Aramid- fiber honeycomb panel with

air in the honeycomb

04 Aramid-fiber honeycomb panel with

polyimide foam in the honeycomb

05 Phenolic-resin panel reinforced

with- glass-filaments

29.,5 1 ..16 610 X 610 24 X 24

32.,0 1 ..26 605 X 600 24 X 24

26..1 1 ..03 614 X 610 24 X 24

26..2 1.,03 611 X 611 24 X 24

6..1 0 ..24 609 X 509 24 X 20

3.j Fibrous-Glass Board Specimens (Samples 01 and 02)

The insulated galvanized-steel and aluminum panels, samples 01 and 02,

were removed from shipboard air ducts. The specimens consisted of a metal

substrate (the duct wall) with a nominal 25 mm thick (1 in.) fibrous -glass

board laminated to the metal substrate. The fibrous-glass board was

finished with a thin sheet (0.08 mm; 0.003 in.) of glass-cloth lagging.

For the thermal measurements, the fibrous-glass boards with lagging

were removed from their respective metal substrate. The specimens were

placed in an oven at 90°C (194°F) for 24 hours prior to measurement.

Measurement of the specimen mass indicated a moisture content of less than

1% (by mass) for both specimens before drying.

3.2 Aramid- Fiber Honeycomb Panels (Samples 03 and 04)

The aramid-fiber honeycomb specimens, samples 03 and 04, were smooth,

rigid panels, both approximately 26 mm (1 in.) thick. The top and bottom

surfaces of both panels were finished with three plies of glass and resin.

The interior of each panel consisted of a honeycomb lattice for structural

support. Individual cells of the honeycomb were hexagonal in geometry and

the walls of the cells were comprised of an aramid-fiber paper. The cells

traversed the entire thickness of each specimen. Details of a panel are

illustrated in Figure 3.

2
The two specimens, while similar in construction, used different

materials to fill the honeycomb cells. Sample 03 had air in the cells,

while sample 04 had polyimide foam foamed in the honeycomb cells during

the manufacture of the panel.

3.3 Phenolic -Res in Panel (Sample 05)

The phenolic-resin panel, sample 05, was a thin (6.1 mm), rigid panel

of phenolic resin reinforced with filament -wound glass fibers. The

filaments of glass-fiber were wound at alternating angles of approximately

±80° in parallel layers within the resin. The specimen surface of the

phenolic-resin panel contained many irregularities, i.e., small pock marks

and ridges of resin. The specimen was also slightly warped. The effect

of these irregularities on the thermal measurements are discussed in

Section 4.

4 THERMAL RESISTANCE MEASUREMENTS

For tests reported here, the NBS 1-m GHP was operated in a one-sided

mode of operation with heat flow (Q) in the vertical direction (up)

Tests were performed in accordance with procedures described in ASTM test

method C-177 and practice C-1044 [4,5]. The backflow specimen was a 101.6

mm thick (4 in.) sample of expanded polystyrene, molded beads. Thermal

measurements were conducted at a mean specimen temperature (Tm ) of 23.9°C

(75°F). Tests were conducted under atmospheric conditions with air as the

ambient fill-gas in the environmental chamber. The relative humidity (rh)

of the laboratory ambient was controlled at 38% ±2% rh.

As mentioned, the fibrous-glass specimens were conditioned in a hot-air

oven at 90°C (194°F) and uncontrolled humidity for 24 hours prior to

thermal measurement. Mass measurements prior to thermal measurement

indicated a moisture content of less than 1% (by mass) for the specimens.

The composite-material specimens were conditioned at 21°C (70°F)38%

rh for a minimum of 6 days prior to thermal measurements . Measurements of

the specimen mass made before and after thermal testing indicated no

significant change (less than 0.05%) in the mass of these specimens during

thermal measurements

The thermal resistance measurement of the phenolic-resin panel posed

several difficulties, not only due to surface irregularities, but also

because the thickness (see Table 1) was less than can be tested directly

with the NBS 1-m GHP (19.1 mm; 0.75 in.). The resistance was instead

determined by the "difference principle" described previously by NBS [6].

In this method, the phenolic-resin panel was sandwiched between two

specimens of five-year old, extruded polystyrene and the thermal

resistance for the stacked assembly measured. The two stacked specimens

of polystyrene were then measured alone. The difference between the two

3
measurements provided the thermal resistance of the phenolic-resin panel,

but also included the effect of contact resistance between the composite

board and polystyrene.

The thermal resistance (R-value) , thickness (L) , bulk density (p)

,

plate temperatures (TH and Tc ) , mean temperature (Tm ), and the change in

mass (AM) for the five specimens are summarized in Table 2. The

uncertainties of the resistance measurement for the fibrous-glass board

and aramid- fiber honeycomb panels were estimated to be ±0.5% [3] and

±1.0%, respectively. The uncertainty in the value of thermal resistance

of the phenolic-resin panel was estimated within ±5% due to the contact

resistance

.

5 DISCUSSION

5.1 Fibrous-Glass Board Specimens (Samples 01 and 02)

The thermal resistance of the fibrous-glass board specimens was

compared with the certified values of NBS Fibrous-Glass Board, SRM 1450a

[7]. From the NBS SRM 1450a certificate, the following equation was used;

L L

R = — = —

A(p,T) ( ao al P ^ a2

3

)

( 1 )

where

,

R =

L = A(p,T) =

p =

T =

m

thermal resistance, (m2 *K/W)

thickness, (m)

apparent thermal conductivity, (W/m*K)

bulk density, (kg/m3 ), and

mean specimen temperature, (K)

.

The values of the coefficients used were;

a0 = 1.930 -x 10“ 2 (W/m*K)

a : = 1.534 x 10” 5 (W»m2 /K*kg)

a2 = 4.256 x 10” 10 (W/m-K4

)

.

For sample 01, the calculated thermal resistance was 0.8065 m

2 *K/W

(4.580 f

t

2 • °F*h/Btu) , or within 2.8% of the measurement reported in Table

2. For sample 02, the calculated resistance was 0.7994 m

2 *K/W (4.539

ft2 •F »h/Btu) , or within 0.7% of the measurement reported in Table 2.

4
5.2 Aramid-Fiber Honeycomb Panels (Samples 03 and 04)

The thermal resistance of the aramid-fiber honeycomb panels was about

one-half the thermal resistance of an equivalent 25 mm thick specimen of

fibrous-glass board. The resistance measured for the panel having air in

the honeycomb cells was 0.355 m

2 »K/W (2.02 ft2 • °F*h/Btu) . The resistance

measured for the panel having polyimide foam in the honeycomb cells was

0.467 m

2 »K/W (2.65 f2 • °F»h/Btu) , an increase of 31% over the panel with

only air in the honeycomb. A detailed analysis of the heat transfer

through the panels is outside the scope of this report, however, a brief

explanation for the difference in R-values is presented.

As described previously, the honeycomb cells traversed the thickness of

the panel providing the means for thermal bridging through the panel and

reducing its thermal performance. Heat transport through an airspace

takes place by radiation, and by convection and conduction combined [8].

Thermal measurements indicated replacing the air in the honeycomb with

polyimide foam provided a moderate increase (31%) in the thermal

resistance of the honeycomb panel. This implies that a significant

portion of the over-all heat transport through the panel having air in the

honeycomb was by radiation and air convection in the cells. Replacing the

air in the cells with foam reduced the radiative and convective heat

transport, resulting in the higher R-value for the panel with foam in the

honeycomb

5.3 Phenolic -Res in Panel (Sample 05)

The thermal resistance of the phenolic-resin panel was determined by

the difference of the two measurements in Table 2. The resistance was

0.058 m

2 »K/W (0.33 ft2 • °F«h/Btu) for a 6.1 mm thick (0.24 in.) panel.

Difficulties with the specimen surface and thickness compounded the effort

for an accurate (1%) determination of the thermal resistance. An

uncertainty of ±5% was estimated for the uncertainty in the resistance

measurement of the stacked assembly due to the contact resistance.

However, this value is provided as a guide only. Further work is needed

to quantify the effect of thermal contact resistance on the specimen

measurement

6 CONCLUSIONS

Thermal resistance measurements of five specimens used in shipboard air

duct systems of the U.S. Navy were conducted using the NBS 1-m Guarded Hot

Plate. Measurements were conducted at a mean specimen temperature of

23.9°C (75°F) at atmospheric conditions. Specimens of fibrous -glass board

were conditioned at 90°C (194°F) prior to measurement. The fibrous - glass

boards were found to be the most efficient thermally, having a thermal

resistance of 0.79 m

2 *K/W (4.5 ft2 • °F*h/Btu) at a thickness of 25.4 mm

(1.00 in.). Resistance measurements were in good agreement (3%) with

5
certified values of NBS SRM 1450a, fibrous-glass board.

The thermal resistance of two aramid- fiber honeycomb panels was about

one-half the thermal resistance of an equivalent 25 mm thick specimen of

fibrous-glass board. The resistance of the panel having air in the cells

of the honeycomb was 0.355 m

2 «K/W (2.02 f

t

2 • °F«h/Btu) at a thickness of

26.1 mm (1.03 in.). The resistance of a second panel having polyimide

foam in the cells was 0.467 m

2 -K/W (2.65 ft2 « °F«h/Btu) , an increase of 31%

over the panel having air in the honeycomb. These measurements suggest

radiative and convective heat transport occurred in the panel having air

in the honeycomb cells. Replacing the air with foam in the cells reduced

the radiative and convective heat transport in the panel, thereby

increasing its R-value . Further work is suggested to analyze the heat

transfer through these honeycomb panels.

The fifth specimen' was a phenolic-resin panel reinforced with glass

filaments. Considerable difficulty in the measurement of thermal

resistance was experienced due to the surface condition and specimen

thickness. The resistance of the phenolic-resin panel was determined by

difference to be 0.058 m

2 «K/W (0.33 ft2 • °F«h/Btu) for the 6.1 mm thick

(0.24 in.) board. This value contains considerable uncertainty due to

contact resistance during the measurement and is discussed in the report.

7 REFERENCES

1. Hahn, M.H.

,

Robinson, H.E. and Flynn, D.R.

,

"Robinson Line-Heat-Source

Guarded Hot Plate Apparatus," Heat Transmission Measurements in Thermal

Insulations. ASTM STP 544 . American Society for Testing and Materials,

1974, pp. 167-192.

2. Powell, F.J. and Rennex, B.G., "The NBS Line-Heat-Source Guarded Hot

Plate For Thick Materials," Proceedings of the ASHRAE/DOE Conference on

the Thermal Performance of the Exterior Envelopes of Buildings - II . Las Vegas, Nevada, USA, December 1982.

3. Rennex, B.G, "Error Analysis for the NBS 1016 mm Guarded Hot Plate,"

NBSIR 83-2674 . National Bureau of Standards, Gaithersburg, Maryland,

USA, February 1983.

4. ASTM 1986, "Standard Test Method for Steady-State Heat Flux

Measurements And Thermal Transmission Properties By Means Of The

Guarded-Hot-Plate Apparatus," 1986 Annual Book Of ASTM Standards . Vol 04.06, ASTM C-177-85, Philadelphia: American Society for Testing

and Materials, 1986, pp . 21-36.

6
5. ASTM 1986, "Standard Practice for Using The Guarded-Hot-Plate

Apparatus In The One-Sided Mode To Measure Steady-State Heat Flux

And Thermal Transmission Properties," 1986 Annual Book Of ASTM

Standards, Vol 04.06 ASTM C-1044-85, Philadelphia: American Society

for Testing and Materials, 1986, pp . 685-688.

6. Robinson, H.E. and Flynn, D.R.

"The Current Status Of Thermal

Conductivity Reference Standards At The National Bureau Of Standards,"

NBS Report-8300 . National Bureau of Standards, Washington D.C., March

1964.

7. Siu, M.C.I., Watson, T.W. and Peavy, B.A., "National Bureau of

Standards Certificate, Standard Reference Material 1450a, Thermal

Resistance - Fibrous Glass Board," February 12, 1979.

8. Robinson, H.E., Cosgrove, L.A.

and Powell, F.J., "Thermal

Resistance of Airspaces and Fibrous Insulations Bounded by

Reflective Surfaces," NBS Building Materials and Structures Report

151 . National Bureau of Standards, Washington D.C., November 1957.

8 ACKNOWLEDGEMENTS

The authors express appreciation to the Department of the Navy whose

sponsorship made this study possible. Program coordination was provided

by Mr. George Wilhelmi and Mr. Minor Appleman of the David Taylor Naval

Ship Research And Development Center.

7
Table

2.

Summary

of

Thermal

Resistance

Measurements

for

All

Specimens

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Fig. 1. The NBS 1-metre Guarded Hot Plate.

9
25

to

380mm

,

,

25

10

380mm

COLD PLATE

Fig. 2. Principle of measurement for the NBS 1-metre Guarded Hot Plate

in a two-sided mode of operation.

10
Fig. 3. a) Honeycomb structure of the aramid-fiber honeycomb specimens.

Dimensions of the specimen are nominal.

b) Detail of the honeycomb lattice. The cells of the lattice

are filled with either polyimide foam or air.

c) Detail of the honeycomb cell.

11
NBS-114A (REV. 2-80

! 'J.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

I SHEET (See in struction s)

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

NISTIR 88-3861 October 1988

I 4. TITLE AND SUBTITLE

iI, Room-Temperature Thermal Resistance Measurements of New and Existing Materials for

Shipboard Air Duct Systems

i

5. AUTHOR(S)

Robert R. Zarr and Thomas A. Somers

6. PERFOR ING ORGANIZATION (If joint or other than NBS, see in struction s) NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

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

Department of the Navy

David Taylor Naval Ship Research and Development Center

Bethesda, Maryland 20084

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

bi bl io graphy or literature survey, mention it here)

Thermal’ resistance measurements of conventional and composite material insulation for

shipboard air duct systems are described. Conventional shipboard air ducts are

constructed of metal walls insulated externally with fibrous-glass board. Composite

materials are being considered as replacements for these duct walls. Thermal

measurements were conducted using the National Bureau of Standards 1 -metre Guarded Hot

Plate at a mean temperature of 23.9°C (75°F)

.

Measurements of the fibrous -glass board

specimens were within 3% of certified values of NBS SRM 1450a, fibrous-glass board.

Measurements of two aramid- fiber honeycomb specimens were approximately one -half the

thermal resistance of the fibrous-glass board specimens.

12.

KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names ; and separate key words by semicolon s) aramid fiber; fibrous-glass insulation; composite materials; guarded-hot-plate

apparatus; polyimide foam thermal resistance

13.

availability

_X Uni united -or Official Distribution. Do Not Release to NTIS

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

20402.

~y Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15

15. Price

$ 9.95

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