NA,r,L INST. OF STAND & TECH NBS

PUBLICATIONS A11107 370353

NBSIR 83-2766 60

Environmental Tests of A

450 Cubic Foot Air Transportable

Field Refrigerator

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Washington, DC 20234

June 1 983

Issued September 1983

I

—»QC«

100

. U56

83-2766

1983

c. 2

Prepared for: Army

;k Research and Development Laboratories

:k, MA 01760

NBSIR 83-2766

* •*- % ENVIRONMENTAL TESTS OF A

450 CUBIC FOOT AIR TRANSPORTABLE

FIELD REFRIGERATOR

Gcjoo

no. n

im

William J. Mulroy

David K. Ward

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Washington, DC 20234

June 1 983

Issued September 1983

Prepared for: U.S. Army

Natick Research and Development Laboratories

Natick, MA 01760

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

- Qt c

^746
- « r
TABLE OF CONTENTS

1. INTRODUCTION 1

2. DESCRIPTION OF TEST SPECIMEN 3

3. TEST SET UP AND INSTRUMENTATION 5

4. REFRIGERATOR THERMAL TRANSMITTANCE TEST 7

5. 43. 3°C (110°F) CONDENSER ENTERING AIR TEMPERATURE

CAPACITY TESTS 8

6. 51. 7°

C

(125 °F) AMBIENT AIR TEMPERATURE PULLDOWN

AND CAPACITY TESTS 12

7. EFFECT OF SOLAR RADIATION 15

8. CONCLUSIONS ....... ....... . 18

9. REFERENCES 19

iii
ABSTRACT

The National Bureau of Standards performed environmental tests on a newly

developed 450 cubic foot air transportable field refrigerator for the U.S. Army

Natick Research and Development Laboratories. The refrigerator, in assemblage

with a supplied refrigeration unit, was found to be more than capable of pulling

down to and holding an interior temperature of -17. 8° C (0°F) when surrounded

by an ambient temperature of 50.4°C (123°F) . Additional tests indicated that

the performance of this assemblage would exceed that required to meet any likely

combinations of sensible and radiant (solar) heat gain.

Key words: field refrigerator; frozen food storage; military refrigerators;

refrigerator assemblage testing; refrigerators; walk-in refrigerators
1.

INTRODUCTION

This report covers work done by the National Bureau of Standards (NBS) in

response to a request by the United States Army Natick Research and Development Laboratory under Natick Project Order 83-186, dated April 8, 1983, to

perform environmental testing on a newly developed 450 cubic foot air transportable field refrigerator.

Environmental tests conducted included:

1. Reverse heating leakage without refrigeration unit installed in

refrigerator. This test was a measurement of the refrigerator thermal

transmittance (UA) by the internal heating method. This thermal

transmittance value is used in calculating refrigeration unit

capacity, refrigeration load at various ambient temperatures , and as

a measure of the insulating quality of the refrigerator.

2. Capacity test at -17.8°C (0°F) when ambient temperature was 37.8°C (100°F)

.

This test was performed to determine whether the refrigeration unit

was performing at its rated capacity. The actual rating conditions

for the refrigeration unit were -17.8°C (0°F) average air temperature entering the evaporator and 43.3°C (110°F) average air temperature entering the condenser.

3. Pull down test at a 51.7°C (125°F) ambient condition. For this test

the unit was started and allowed to pull the refrigerator temperature

down to -17.8°C (0°F) in a 51.7°C (125°F) ambient after an extended
thermal stabilization period in this ambient. This is an operational

test that measures the unit's ability to operate with high load on the

compressor as a result of high suction and discharge pressures.

4. Capacity test at -17.8°C (0°F) with a 51.7°C (125°F) ambient. This

test was- used with the rating point test (2) to estimate the unit

performance, by interpolation, at other high ambient temperatures.

5. Determination of the ability of the assemblage to maintain -17.8°C

(0°F) under solar conditions by calculating from the above test data.

These calculations were performed based on the "sol-air" concept as

presented in Chapter 26 of the American Society of Heating, Refrigerating and Air-Conditioning Engineers Handbook of Fundamentals [1]

and the environmental conditions of Military Standard 810c.

2
2. DESCRIPTION OF TEST SPECIMEN

The walk-in refrigerator was shipped directly from its manufacturer, R.S.P.

Industries Inc.,* 329 Herzl Street, Brooklyn, New York 11212, to the National

Bureau of Standards. Nameplate data were, in addition to the manufacturer’s

identity, Model No. AA-450-WPR; Contract No. DAAK60-82-M-4117 ; and Serial

No. 83-3-0757.

It was measured to be 2.36 m (7 ft. 9 in.) wide, 3.66 m (12 ft.) long, 2.29 ra

(7 ft. 6 in.) high to the extremes of the insulated shell exterior, and 2.43 m

(7 ft. 11 1/2 in.) high to the bottom of its integral skid. The doorway was

0.91 m (3 ft.) wide and 1.83 m (6 ft. high). The unit hole was 0.72 m (28 1/2 in.)

square. The wall thickness was 102 mm (4 in.).

The nameplate data of the refrigeration unit were:

Refrigeration Unit, Mechanical Type II

Capacity: 5,000 Btu, 0°F Refrig.

7,500 Btu, 35°F Refrig.

Refrigerant: 12

Charge: 136 oz. NSN : 4110-01-092-3913

Model No.: REMD-G/ll-VI-S

Serial No . : TAG-116

Power Supply: 208 v., 3 phase, 60 cycle

Manufacturer: A.R.E. Mfg. Co., Inc.*

Frederick, Maryland

*This report was prepared as an account of work sponsored by an agency of the

United States Government. Neither the United States Government nor any agency

thereof, nor any of their employees, makes any warranty, express or implied,

or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

Reference herein to any specific commercial product, process or service by

trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favoring by the United States

Government or any agency thereof. The views and opinions of authors expressed

herein do not necessarily state or reflect those of the United States

Government or any agency thereof.

3
As received the unit had 96 hours on its running time meter. During initial

checkout it was observed that the unit had lost pressure and, upon pressurizing

the system, the vibration eliminator in the compressor suction line was found

to be leaking. This defective part was replaced and the unit evacuated and

recharged prior to performance of the test series described in this report.

4
3. TEST SET UP AND INSTRUMENTATION

The refrigerator was placed for testing in the largest of the NBS environmental

chambers of nominal dimensions 14.9 m long x 12.8 m wide x 9.4 m high

(49 ft. long x 42 ft. wide x 31 ft. high). This chamber had an earthen floor

which was covered with 19 mm (3/4 inch) plywood to a distance of approximately

0.6 m (2 ft.) beyond the refrigerator outside dimensions. The refrigerator was

supported on concrete blocks to provide a 0.3 meter (1 ft.) air space beneath

it to insure a uniform surrounding ambient temperature. There was an additional

122 mm (4 13/16 in.) air space incorporated in the refrigerator between the

bottom of its insulated floor and the bottom of its integral skid.

Individual Type T thermocouples were installed at each interior and exterior

comer of the refrigerator at a distance of 150 mm (6 in.) from the surface.

Additional averaging thermocouples were installed in the refrigerator interior

to assist in test set up and for connection to the heater controller.

Electrical resistance heat to the refrigerator interior was provided by a single

1.5 kW, 208 v heater placed at the center of its floor. A separate 110 v circulating fan was placed at the unit end of the refrigerator pointed directly at

the heater. The power lines were passed out of the unit through the floor

drain hole which was located at the unit end of the refrigerator. The controller for the heater power and the watt hour meters for the heater and the fan

were located in the test chamber control room.

For the reverse direction heat loss test, a plug constructed of 100 mm (4 in.)

of extruded polystyene insulation (two 50 mm pieces) was placed in the unit

5
hole and sealed on the inside with duct tape and sheathed on the outside with

19 mm (3/4 in.) plywood.

The refrigeration unit was instrumented with a 4-junction averaging thermocouple measuring the temperature of air entering the evaporator. Another

4-junction averaging thermocouple measured the temperature of air entering

the condenser. For later tests, thermocouples were added to the vapor line

at the expansion valve bulb and downstream from the liquid line to the suction

line heat exchanger to allow evaluation of the expansion valve setting. For

all tests the unit power consumption was read and recorded from a three-phase

watt-hour meter. The unit suction and discharge gauges were read and recorded

during all tests. The unit suction gauge was checked for its zero setting

and found to be reading 24 kPa (3.5 psig) high, which required corrections to

be made to the reported data.

6
4. REFRIGERATOR THERMAL TRANSMITTANCE TEST

The refrigerator thermal transmittance was measured using the reverse-direction

(heated interior) heat loss method in which the ambient temperature surrounding the refrigerator was maintained at approximately -17.8°C (0°F) and the

refrigerator interior temperature was maintained at approximately 37.8°F (100°F)

by an automatically-controlled, metered electrical resistance heater and circulating fan.

For this test only, the insulated plug described in Section 3 was substituted

for the refrigeration unit. The heat loss through the plug was calculated

following the procedures in Chapter 23 of the ASHRAE Handbook [1] at 0.13 W/°C

(0.25 Btu/h°F) . This value was subtracted when calculating the refrigerator

thermal transmittance.

Prior to taking test data, thermal conditions were allowed to stabilize for 25

hours after the nominal interior and ambient test temperatures had been

achieved. Test data were taken for a period of 24 hours with the following

summarized results

.

Average ambient air temperature

Average refrigerator temperature

Average temperature difference

Mean wall temperature

Power to resistance heater

Circulating fan power

Refrigerator thermal transmittance

—17 , 9°C (—0 . 3°F)

37.5°C (99 . 5°F)

55.4°C (99.8°F)

9.8°C (49 ,6°F)

482.8 W

102.9 W

10.44 W/°C (19.8 Btu/h°F)

The above listed mean wall temperature is the average of the listed ambient and

refrigerator temperatures calculated as specified in Section 8.18.1 of American

National Standard MHS . 1 . 2M-1980 [2],

7
5. CAPACITY TESTS WITH 43.3°C (110°F) CONDENSER ENTERING AIR TEMPERATURE

Following the reverse direction thermal transmittance test described

in Section 4, a measurement was made of the capacity of the refrigeration unit

with a condenser entering air temperature of 43.3°C (110°F) . For this test

the unit was installed in the refrigerator in place of the insulated plug

used in the thermal transmittance tests. The unit was then operated to maintain an average temperature of approximately -17.8°C (0°F) within the

refrigerator and the ambient temperature surrounding the refrigerator raised

to the level necessary to provide a condenser entering air temperature of

43.3°C (110°F). After air temperatures had been attained, an additional 24

hours were allowed to elapse in order to obtain thermal equilibrium before

data were taken. The unit was not allowed to cycle for this test, the thermostat being turned down to its lowest setting and the automatic controller for

the electrical resistance heaters which had been installed in the refrigerator for

the test series being set to control at -17.8°C (0°F). After thermal equilibrium had been achieved, the unit was defrosted, yielding approximately 600 ml

(20.5 fl. oz) of water. It was then returned to steady-state operating conditions and the following data were observed over a six-hour period:

Average air temperature entering condenser

Average discharge pressure

Average air temperature entering evaporator

Average suction pressure

Average ambient temperature

Average refrigerator temperature

43 . 3°C (110. 0°F)

1,270 kPa (169 psig)

-17 . 9°C (-0 . 2°F)

86 kPa (-2.2 psig)

42 .0°C (107. 7°F)

-17 . 8°C (-0.1°F)

8
Refrigerator heat gain 625 W (2133 Btu/h)

Electrical resistance heat 405 W (1383 Btu/h)

Unit capacity 1030 W (3516 Btu/h)

Average unit power draw 2.5 kW

Unit efficiency, COP 0.41

The refrigerant liquid line sight glass was observed to be clear during the

above data period.

This test was followed by a 51.7°C (125°F) ambient temperature pulldown and

capacity test as described in Section 6. At the completion of the 51.7°C

(125°F) ambient test it was decided to rerun the above reported 43.3°C (110°F)

capacity test since the measured capacity of 1030 W (3516 Btu/h) was substantially below the rated capacity for the unit of 1465 W (5000 Btu/h) . Prior to

this rerun, thermocouples were attached to the suction line at the thermal

expansion valve bulb and immediately after the heat exchanger to provide a measure of the adequacy of the unit charge and expansion valve setting. Also prior

to this rerun, the unit-to-ref rigerator seal was taped to insure against air

infiltration at this point. When thermal conditions had been reestablished

following a procedure similar to that for the first test, the unit capacity was

found to have unaccountably increased. The defrost water recovered prior to

this test was approximately 300 ml (10.1 fl. oz) after approximately 12 hours of

running. This frost collection rate of 25 ml/h versus the previous comparable test's 27 ml/h is clearly not responsible for the change in unit

capacity

.

The thermocouple on the suction line indicated a cycle with occasional flooding through the heat exchanger indicating that neither increased charge nor

expansion valve superheat adjustment would be likely to increase capacity. The

summarized observed performance for this test was:

9
Average air temperature entering condenser 43 . 5°C (110. 3°F)

Average discharge pressure

Average air temperature entering

Average suction pressure

Average ambient temperature

Average refrigerator temperature

Refrigerator heat gain

Electrical resistance heat

Unit capacity

Average unit power draw

Unit efficiency, COP

1,290 kPa (172.3 psig)

evaporator -17.8°C (-0.2°F)

101 kPa (-0.1 psig)

42 . 4°C (108. 3°F)

-17. 7°C (0.2°F)

626.8 W (2139.2 Btu/h)

561.6 W (1916.6 Btu/h)

1188.3 W (4055.8 Btu/h)

2.55 kW

0.47

For this test the stabilization period was 16 hours and the data period was 9

hours. As before, the refrigerant sight glass was clear throughout the data period.

The increase in suction pressure from the previous test without change

in evaporator entering air temperature would indicate that a change in unit

performance did occur as a result of some change internal to the refrigeration

unit such as a particle of dirt partially blocking the expansion valve orifice.

The observed suction pressure which was equivalent to — 24. 8° C (— 12.6°F) saturated

suction temperature at the compressor and the cyclic flooding into the heat

exchanger would indicate that the unit was operating properly during this repeat test

The ambient dew point for these tests was maintained at approximately 15.6°C

(60°F) which, at a dry bulb temperature of 43.3°C (110°F) , corresponds to a

relative humidity of approximately 20%.

10
y following this test the 51.7°C (125°F) pulldown and capacity test

was repeated.

•

‘

••

'
6. PULLDOWN AND CAPACITY TESTS WITH 51.7°C (125°F) AMBIENT AIR TEMPERATURE

Each of the 43.3°C (110°F) condenser entering air temperature capacity tests

discussed in Section 5 was followed by a 51.7°C (125°F) ambient temperature

pulldown and capacity test.

For the first of the indicated tests the refrigerator, with its door open, was

allowed to come to thermal equilibrium for a period of 16 hours after its exterior and interior air temperatures had reached the value of approximately 51.7°C

(125°F). At the end of this period the door was closed and the unit started.

After 1 hour and 20 minutes of operation the refrigerator interior temperature

had reached an average of 1.7°C (35°F). After 6 hours and 30 minutes from unit

start-up, the refrigerator interior temperature had reached an average value of

-17.8°C (0°F) . The metered electrical resistance heaters which had been installed.

in the container were then energized with their automatic controller set to

maintain the refrigerator interior temperature at -17.8°C (0°F) and the unit was

run for an additional 24 hours to allow thermal conditions to stabilize before

steady-state data were taken. The unit was defrosted yielding approximately

500 ml (16.9 fl. oz.) of water five hours before the steady-state data were taken.

The summarized data for the steady-state period are as follows:

Average air temperature entering condenser 52.6°C (126. 6 °F)

Average discharge pressure 1,515 kPa (205 psig)

Average air temperature entering evaporator -17.8°C (-0.1°F)

Average suction pressure 98 kpa (-0.5 psig)

12
Average ambient temperature 50 .4°C (122. 7°F)

Average refrigerator temperature -17 . 7 °C (0.1°F)

Refrigerator heat gain 711 W (2425 Btu/h)

Electrical resistance heat 101 W (346 Btu/h)

Unit capacity 812 W (2771 Btu/h)

Average unit power draw 2.56 kw

Unit efficiency, COP 0 332

As discussed in Section 5, this test was followed by a repeat 43.3°C (110 °F)

condenser entering air air unit capacity test and then was itself repeated.

For the repeat 51.7°C (125°F) pulldown and capacity tests, the refrigerator

was allowed to come to thermal equilibrium for a period of 10 hours with its

door open after its exterior and interior air temperature had reached a value

of approximately 51.7°C (125 °F) . At the end of this period the door was

closed and the unit started. After 1 hour and 18 minutes of operation, the

refrigerator interior temperature had reached an average value of 1.7°C (35°F)

.

After 5 hours from unit start-up the refrigerator interior temperature had

reached an average value of -17.8°C (0®F) . As before, the metered electrical

resistance heaters were then energized with the automatic controller set to

maintain the refrigerator interior temperature at -17.8°C (0°F) and the unit

ran for a short additional period (two hours) before the following steady-state

data were taken:

Average air temperature entering condenser 52.6°C (126. 7°F)

Average discharge pressure 1510 kPa (204.5 psig)

13
Average air temperature entering evaporator -17 . 7°C (0 . 1°F)

Average suction pressure 92 kPa (-1.4 psig)

Average ambient temperature 50.4°C (122. 8°F)

Average refrigerator temperature -17.4°C (0 . 6°F)

Refrigerator heat gain 708 W (2417 Btu/h)

Electric resistance heat 108 W (369 Btu/h)

Unit capacity 816 W (2786 Btu/h)

The results of this test are not substantially different from those of the

previous 51.7°C (125°F) test.

The ambient dew point for these tests was maintained at approximately 15.6°C

(60°F) which, at a dry bulb temperature of 51.7°C (125°F) , corresponds to a

relative humidity of 15 percent.

14
7. EFFECT OF SOLAR RADIATION

A popular way of handling the effect of solar radiation on cooling load is the

sol-air concept as described in the air-conditioning cooling load chapter of

the American Society of Heating, Refrigerating, and Air-Conditioning Engineers

Handbook of Fundamentals [1]* The sol-air temperature, t^, is calculated

from the equation

:

t = t + ai. /h - eAR/h.

e o t' o o

where

a = absorptance of the surface for solar radiation.

2 2 I = total solar radiation incident on the surface, W/m (Btu/(h • ft ))

h = coefficient of heat transfer by long wave radiation and convection

° at the outer surface, W/ (m^ • °C) (Btu/ (h • ft^ • F) )

.

t Q = outdoor air temperature, °C (F)

.

e = hemispherical emittance of the surface

AR = the difference between the longwave radiation incident on the surface

from the sky and surroundings, and the radiation emitted by a blackbody at outdoor air temperature, W/m^ (Btu/(h • ft;).

For horizontal surfaces that receive longwave radiation from the sky only, such

as the roof of this refrigerator, Chapter 26 of the ASHRAE Handbook [1] recommends a value of -3.9°C (-7°F) for the longwave reradiation correction term,

£AR/h

Q

. The ASHRAE recommended maximum value (i.e., for dark-colored surfaces)

for a/h

Q

is 0.052 (0.30). The maximum value for direct, normal 1^ given in the

2

ASHRAE tables of solar intensity in Chapter 27 of reference [1], 1058 w/'m

(335 Btu/ (h • ft^)), corresponds to the maximum value specified by MIL-STD-810c

[3]. Substituting these numbers gives:

15
t = t + (0.052) (1058) - 3.9 = t + 51.1°C (92°F)

e o o

Since this sol-air temperature should only be applied to the roof of the container, a new sol-air temperature, t g can be defined by reducing the term

to be added to the ambient by multiplying by the mean roof area divided by the

total mean insulated surface area. Mean areas are the mean of the inside and

2 outside areas of each surface. The roof area of this container is 8.04 m

2 2 2 (87 ft ) and the total mean area is 41.49 m (447 ft ), hence:

t = t + (51.1) (8.04) /41. 49) = t + 9 . 9 °C (17.8°F)

e , amb o o

A similar calculation can be made for the other high ambient test point of

MIL-STD-810c [3] which, when used with the refrigerator thermal transmittance

measured in Section 4, gives the unit capacity requirements in Table 1.

Table 1. Unit Capacity Requirements

Amb lent Solar Unit Capacity

Temperature r\ Radiation „n £ e ,amb Requirement

°C ( °F) W/nr (Btu/ (h • ft )) °C(°F) W (Btu/h)

47 . 8°C 1058 59.2 801

(118) (335) (138.6) (2744)

48.9°C 739 55.6 764

(120) (234) (132.1) (2616)

Since the unit capacity measured in a 50.4°C (122. 8°F) ambient was 816 W (2786

Btu/h) and increased at lower ambient temperatures, these requirements are

clearly met under the assumption that for calculating refrigeration load the direct solar normal incident radiation criteria should only be applied to the surface

area of the refrigerator roof. The question of whether a higher total radiation

16
load would result from assuming angular incident radiation covering the roof

and one side and the effects of mass storage in producing a coincident load

peak were not investigated.

17
8. CONCLUSIONS

Although this particular refrigeration unit was operating somewhat below its

rated capacity, it was able to pull down the refrigerator interior temperature

from 51.7°C (125°F) to -17.8°C C0°F) in a 51.7°C (125°F) ambient and to hold

the refrigerator interior temperature at -17.8°C (0°F) in that same ambient

temperature with sufficient extra capacity to meet a likely solar load. It

can therefore be concluded that the assemblage of this refrigerator with a 1460 W

(5000 Btu/h) refrigeration unit would be expected to perform adequately in the

field with respect to maintaining required refrigeration temperatures, even

with some degradation of unit and/or refrigerator performance.

18
9. REFERENCES

1. "ASHRAE 1981 Handbook of Fundamentals", American Society of Heating,

Refrigerating and Air Conditioning Engineers, Atlanta, Georgia 30329.

2. "American National Standard MH5 .1.2M-1980, Requirements for Thermal Van

Containers (Refrigerated, Heated, and Insulated)", American Society of

Mechanical Engineers, New York, New York 10017.

3. "Environmental Test Methods", Military Standard 810c, 1975, Aemoautical

Systems Division, Wright-Patterson Air Force Base, Ohio 45433.

19

NBS-1 14A irev. 2-aci U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

83-2766

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

September 1983

4. TITLE AND SUBTITLE

Environmental Tests of a 430 Cubic Foot Air Transportable Field Refrigerator

5. AUTHOR(S)

William J. Mulroy and David K. Ward

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

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

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

U.S. Army

Natick Research and Development Laboratories

Natick,, MA 01760

10. SUPPLEMENTARY NOTES —

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

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

bi bliography or literature survey, mention it here)

The National Bureau of Standards performed environmental tests on a newly developed

450 cubic foot air transportable field refrigerator for the U.S. Army Natick Research

and Development Laboratories. The refrigerator, in assemblage with a supplied refrigeration unit, was found to be more than capable of pulling down to and holding an interior temperature of -17.8°C (0°F) when surrounded by an ambient temperature of

50.4°C (123°F) . Additional tests indicated that the performance of this assemblage

would exceed that required to meet any likely combinations of sensible and radiant

Csolar) heat gain.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Field refrigerators; frozen food storage; military refrigerators; refrigerator

assemblage testing; refrigerators; walk-in refrigerators.

13. AVAILABILITY

| Unlimited

[~X] For Official Distribution. Do Not Release to NTIS

i

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

20402.

r^~| Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

15. Price

USCOMM-OC 6043-P 80


j)