Electrically powered heat source was developed for ground simulation of isotope heat-source assembly in Brayton power system. Heat source, which operates on ordinary 110 vac power, consists of tungsten filament heating element wound onto a spirally grooved boron nitride core and inserted in a hollowed-out graphite hexahedron

Prok, G. M.

Smith, R. B.

English

NASA Technical Reports Server

---GRAPHITE RETAINER 
BORON NITRIDE CORE 
N
"—Cb-Zr TERMINALS AND SCREWS 
March 1973
	
B73-1001 I 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce new technology derived !rom the U S. space oroeram They are iSSUOd to enc'uraqP 
commercial application Tech Briefs are available on a subscription basis fror, the National Technical Information 
Service. Springfield. Virginia 2215t. Regues;s for individual copies or ctuestion 	 P- relating to h p Tech ': program may 
be directed to the Technology Utilization Office. NASA. Code KT, Washington. D.0 20546 
LOW COST UNIFORM HEAT SOURCE 
TUNGSTEN WIRE WINDINGS 
IN ALUMINUM OXIDE BEADS-1
/ 
FINE GRAINED GRAPHITE—" 
.
	
Figure 1. - Cross section of simulated isotope heat source. 
The Problem: 
A Brayton power system is being developed to provide 
up to 15 kilowatts of electric power for space applica-
tions. In space applications, the heat supply will be an 
isotope heat-source assembly which will radiate heat to 
the working gas contained in a heat exchanger. For 
ground test purposes, a simulated heat source was needed 
which was not radioactive and therefore would not 
require the precautionary practices involved in handling 
an isotope heat source. 
Requirements were: 
I. Power output of 400 watts with the heat-emitting 
surfaces at a temperature of approximately 1 366 K 
(2000-17). 
2. Heat-emitting surfaces of the same size, shape, and 
material as the isotope heat source; i.e., a hexahedron 
17.15 cm (6.75 inches) high and 8.9 cm (3.5 inches) 
across the flats, made of graphite for high emissivity 
and uniform heat flux. 
3. Sufficient operating life expectancy to conduct all 
preliminary testing of the Brayton power system; i.e., 
approximately 5000 hours. 
Available commercial heat sources were too large and 
required large power supplies to meet these requirements.
The Solution: 
An electrically-powered heat source designed and built 
from readily available materials which operates on 
ordinary 110 vac power. 
How It's Done: 
The heat source (Figure 1) consists of a tungsten 
filament heating element wound onto a spirally-grooved 
boron nitride core and inserted in the hollowed-out 
graphite hexahedron. The tungsten filament is designed to 
operate at a temperature of 1588 K (2400°F) with a 
power output of 400 watts. The filament is 0.51 film (20 
mils) in diameter and 21 3 cm (84 inches) in length. The 
boron nitride core is 4.45 cm (1.75 inches) in diameter 
and 15.24 cm (6 inches) in length. An oval-shaped stub on 
one end fits into a slot in the end of the graphite jacket to 
prevent the core from rotating. The opposite end of the 
core is round and fits into a recess in the retaining cap. 
Aluminum oxide beads threaded onto the tungsten 
Filament prevent interaction between the filament and the 
core. The hollow interior of the graphite jacket is 6.35 cm 
(2.5 inches) in diameter. 
-	 (continuvd overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability r nsultinc from :h'- use of the 
Aeronautics and S pace Administration Neither the United States	 information contaoed in this documr . nt. or warrant ,; that such use 
Government nor any person acting on behalf of the United States 	 will be free from pruvatcly owned rights
https://ntrs.nasa.gov/search.jsp?R=19730000011 2020-03-17T06:39:03+00:00Z
POWER 1—THERMOCOUPLE 
LEADS	 LEADS —...
,—FOUR  LAYERS OF 
-'  
IONIZATION
	
	
QUARTZ INSULATION 
-z CAGE
.— Cb -Zr 
wI1.1uiasl..—_ 90.	 INLESS STEEL 1 IF 1, 	 THERMOCOUPLE 
THREE LAYERS OF 
QUARTZ INSuLATION — J'1111 10 .10
ii	 • p 
01 MY 
FIVE LAYERS OF 
QUARTZ INSULATION
- 304 STAINLESS STEEL 
Figure 2. - Cross section of insulated container with heat source installed.
., 
The heat source was tested in an insulated container 
(Figure 2) installed in a vacuum chamber. The insulated 
container was constructed of alternate layers of quartz 
felt insulation and ,thin metal sheets; the metal sheets 
closest to the heat source were columbium-zirconium 
alloy, the outer layers and outer container were 304 
stainless steel. Instrumentation included thermocouples 
embedded in the center of the boron nitride heater core 
and in the surface of the graphite jacket, and current and 
voltage meters for the heater. Three surface thermo-
couples were used to measure the temperature uniformity 
of the radiating surface. 
Thermocouple readings were taken on a two-channel 
recording milli-voltmeter. Pressures in the test chamber 
were measured with ionization gages. 
Notes: 
1. This heat source was successfully operated for over 
5000 hours at rated power and temperature, and was 
successfully cycled six times. Material analysis showed 
no reaction problems between the materials due to the 
high temperature. 
2. The heat source size, shape, and output were dictated 
by the particular application for which it was designed. 
The design principles employed are readily adaptable 
to the design of heat sources for other applications. 
3. As an extension of this design, the graphite jacket can 
be impregnated for evacuation and sealed, thus making 
the heat source suitable for use outside of a vacuum 
environment, at temperatures lower than the oxidation 
temperature of the graphite.
4. The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: NASA TM-X .2374 (N71-34621), Simu-
lated Isotope Heat Source for Use in Brayton 
Power Systems 
Technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B73-10011 
Patent Status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
NASA Patent Counsel 
Mail Stop 500-113 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Source: R.B. Smith and G.M. Prok
Lewis Research Center
(LEW-1 1903)
S 
. 
873-10011	 Category 02


Low cost uniform heat source

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