Document text
General Disclaimer
One or more of the Following Statements may affect this Document
• This document has been reproduced from the best copy furnished by the
organizational source. It is being released in the interest of making available as
much information as possible.
• This document may contain data, which exceeds the sheet parameters. It was
furnished in this condition by the organizational source and is the best copy
available.
• This document may contain tone-on-tone or color graphs, charts and/or pictures,
which have been reproduced in black and white.
• This document is paginated as submitted by the original source.
• Portions of this document are not fully legible due to the historical nature of some
of the material. However, it is the best reproduction available from the original
submission.
Produced by the NASA Center for Aerospace Information (CASI)
TRW 30979-6003-RU-0C
NASA CR 159550
CTS-TYPE
VARIABLE CONDUCTANCE
HEAT PIPES FOR SEP FM/PPU
CONTRACT NAS 3-21130
FINAL REPORT
DECEMBER, 1978
Prepared for v
NASA LEWIS RESEARCH CENTER
CLEVELAND, OHIO, 44153
N79-22434
fjnclas
25103
D. ANTONIUK
E.E. LUEDKE
(NASA-CR-159550) CTS-TYPF VAPIABLP
s'l Zl, nnal
1978 (TPK Defen«;p
and Space Systens Group) 45 p HC A03/!1F^A01
CSCL 20D G3/34
TRW SALES NO. 30979.000
TRW
OffftfU AMO SAACt SYSTtMtS OMOUR
* RCOOP40O SfACM •
ONC «»»ACf RA«»l
CONTENTS
Page
1. INTRODUCTION
1
2. BACKGROUND
2
3. PHASE I
3
3.1
Artery Splicing
3
3.2
Arteries
6
3.3
Gas Reservoir
7
3.4
Artery Priming Tests
7
3.5
Liquid Inventory
8
3.6
Performance Tests
10
3.7
Summary
14
4. PHASE II DESCRIPTION
15
4.1
Final Heat Pipe Design
15
4.2
Heat Pipe Assembly and Processing
15
4.3
Liquid Inventory
15
4.4
Performance Tests
16
4.5
Individual Heat Pipe Summary
19
4.6
Module Assembly
19
4.7
Module Acceptance Test
21
5. SUMMARY AND CONCLUSIONS
25
APPENDIX
A-1
1. INTRODUCTION
Under Contract NAS3-21130, TRW Defense and Space Systems Oroup
has fabricated six variable conductance heat pipes (VCHP's) and
assembled them into two modules of three heat pipes, soldered into
a common aluminum saddle. THese heat pipes have individual capacities
of at least 220 watts at 50°C and are over 310 centimeters long. This
heat pipe design was evolved from the VCHP design which TRW built for
NASA Lewis Research Center as a part of the Transmitter Experiment
Package for the CTS spacecraft.
This report documents the activities conducted under contract
including development effort, complete design details and test results.
1
2. BACKGROUND
TRW Defense and Space Systems Group has been active in heat pipe
development since 1964, and has had considerable experience with flight
heat pipes on CTS, Viking, OAO-C, sounding rockets and other spacecraft.
The use of variable conductance arterial heat pipes on CTS represents
the first time that gas loaded heat pipes have been used in the primary
thermal control system of a spacecraft. THe heat transport capacity of
the individual CTS heat pipes is approximately 7500 watt-inches.
Recognizing the potential application of this technology to
systems such as SEP FM/PPU which have stringent weight limitations, TRW
pursued an Independent Research and Development Program in 1974 and in
1975 to implement improvements in the CTS design aimed at doubling the
capacity. During the I RAD program, two heat pipes were fabricated, one
with 0.70-inch-diameter arteries and one with 0.080- inch-diameter arteries,
both using 0.0027-inch priming foils with a single row of 0.0067-inch-
diameter venting holes. The arteries were placed low in the pipe cross-
section such that a 0.020-inch gap was maintained between the artery and
the tube wall. The lower placement of the arteries was to improve the
ability of the arteries to prime in earth gravity. In addition, a new
priming foil design was conceived that did not impede the liquid entering
it and thus allow priming with a low fluid charge. These changes in the
CTS design were successful in terms of capacity increases but artery
priming was unreliable. The capacity was increased to 14,300 watt-inches
at 0.3-inch evaporator elevation which corresponds to the capacity
predicted in zero gravity. This increase in capacity resulted from the
use of larger diameter arteries and smaller venting holes in the priming
foil. The lower placement of the arteries, however, was believed to be
responsible for the unreliable artery priming.
In 1977, TRW was awarded contract NAS3-21130 by NASA Lewis Research
Center to conduct a two-phase program to develop and test two prototypes
and subsequently, six flight-type variable conductance CTS-type heat pipes
2
each with a 14, 000-watt- inch capacity for SEP application. A two phase
program was called for to confirm that recommended changes in the heat
pipe design would successfully resolve the priming problems encountered
in the IR&D program. During Phase I, two methanol/stainless steel heat
pipes, one with 0.070-inch-diameter arteries and one with 0.80-inch-
diameter arteries, were to be developed and tested. In addition, since
the SEP design calls for an overall heat pipe length of 122.5 inches, the
activities during this phase were to include the development of a tech-
nique to splice the arteries.
Contingent upon successful results from these Phase I development
activities, a design would then be selected for the fabrication of six
variable conductance heat pipes during Phase II. The heat pipes were
to be soldered to aluminum saddles as the final fabrication step.
3
3. PHASE I DESCRIPTION
The objective of this phase of the program was to fabricate and test
two variable conductance heat pipes which incorporated developments
expected to lead to the 14,000 watt-inch capacity goal and to reliable
artery priming.
3.1 ARTERY SPLICING
One of the first activities in this program was the development
of a technique to splice the arteries mandated by the SEP design calling
for an overall length of over 122 inches.
The arteries are fabricated from 150 mesh stainless steel screen,
made using 0. 0026-inch-diameter wire. This material is only available
in 60-inch width. This fact impacts the fabrication of arteries for the
SEP application since it is mandatory to cut the screen on a 45-degree
bias to prevent collapse of the arteries when the 90-degree bend if’ the
heat pipe is formed between the PPL) and the radiator. The longest
single piece of material that is obtained with this mesh pattern is
approximately 80 inches; hence, it was necessary to splice the artery
at some point in the wick structure. Although the slab wick which
supports the arteries also required a splice, a technique for that splice
had already been developed and tested during the CTS program.
A method for splicing the artery was developed and tested. The
concept is to seam weld a 0.75-inch-wide strip of 0.0005-inch stainless
steel foil to the two sides of a butt joint in the mesh screen. The
spliced screen is then used to form the artery following standard manu-
facturing techniques. The drawing of a test specimen is shown in
SK77040 in the Appendix. As shown, the foil in the region of the splices
is inside the artery. The specimen proved to be sufficiently strong to
render unnecessary the use of an additional section of foil on the out-
side of the artery. Photographs of the splice sample are shown in Figure 1.
4
A. Splice Region
i
f
B. Overall Sample
Figure 1. Artery Splice Test Sample
5
Concurrent with these development activities, detailed drawings
for the two heat pipes were prepared. The complete set of drawings is
included in the Appendix. Certain features of the SEP design are
discussed below.
3.2 ARTERIES
The design uses 0.070-inch-diameter and 0.080-inch-diameter arteries.
For the same capillary pressure these arteries can be expected to have a
capacity 1.5 times and 2.5 times respectively larger than the 0.063-inch-
diameter arteries in the CTS design. Following the recommendation made
after the 1974 and the 1975 I RAD programs, the arteries are located in
the tube cross-section such that a 0.040-inch gap exists between the
arteries and the tube wall. The locations of the SEP arteries are shown
sthenatlcally in Figure 2 where they can be compared to the CTS design,
ihis configuration yields essentially the same safety factor for artery
priming as the CTS design. The safety factor is a measure of the ability
of the arteries to prime in earth gravity, which is taken as the ratio of
the capillary pressure of the open artery to the hydrostatic pressure
based on the distance from the bottom of tube to the center of mass of
the artery.
Figure 2. Artery Locations in CTS and SEP Designs
6
The capillary pressure of the arteries is established by the 0.0067-
inch-diameter venting holes in the priming foil. Tiis capillary pressure
is approximately 50 percent greater than the capillary pressure of the
CTS arteries. The SEP priming foil design uses a 0,00027-inch-thick
stainless steel foil section with a single row of venting holes. This
foil is spot welded on the inside of a short stainless steel tube over
a window cut in it.
The inside diameter of the priming tube is 0.001 inch larger than the
inside diameter of the arteries in order to prevent the foil region from
filling with liquid by capillary pressure before the artery primes. This
priming foil design is similar to the one developed during the 1974-1975
IRAD program. Tests have shown that this design does not impede the liquid
from entering it, thus requiring in principle a lower fluid inventory for
artery priming.
3.3 GAS RESERVOIR
The volume of the gas reservoir is identical to that of the CTS
reservoir, which is 8.22 cubic inches. Although the reservoir-to-
condenser volume ratio is approximately 1, compared to the 1.5 to 2.0
ratio in the CTS design, a tighter control range is achieved (26°F
versus 52°F). The improved temperature control range is due to the
fixed, and low, sink temperature of -102°F. Based on the flat gas front
theory, a gas inventory of 6 x 10“® lb-moles should provide a control
range from full off at 91°F to the full on at IH^F.
3.4 ARTERY PRIMING TESTS
Before the arteries were attached to the slab wick, bubble point
tests were performed to establish the integrity of the arteries and the
priming foil .
Subsequently, the slab wick/artery assemblies were subjected to
priming tests in a glass tube containing acetone. Tests results with the
0.080-inch-diameter arteries using 0.081-inch-I.D. priming tubes were
satisfactory. However, priming tests with the 0.070-inch-diameter arteries
using 0.071-inch-I.D. priming tubes showed that priming occurred con-
sistently through the priming cap region and gas was vented through the
screen. It is believed that the small difference in radii (0.070 inch
7
versus 0.071 inch) was insufficient to allow a safety marqin, and slight
deformation in either the tube or foil during the priming cap installa-
tion could have resulted in the priming foil region having a smaller
effective radius than the artery. As a means of guaranteeing that the
priming tube would be last to prime, the 0.081-inch-I .0. priming tube
was also installed on the 0.070-in:h-d1ameter arteries. Subsequent tests
showed this design change resulteo in reliable priming of the 0.070-inch-
diameter arteries.
3.5 LIQUID INVENTORY
A change in the design of the two heat pipes was made in which the
last 4 inches of the evaporator, including the priming foil caps, was
exposed by cutting the tube short. This was done to allow observation
of priming and depriming during the evaluation tests. One of the heat
pipes, complete with heater tape and thermocouples, is shown in Figure 3.
The evaporator end was closed with a glass tube and a Swagelok fitting
using Teflon ferrules as shown in Figure 4. Figures 5 and 6 show the
exposed wick and artery in more detail.
Figure 3. Completed SEP FM/PPU Development Heat Pipe
9
Figure 6. Exposed Evaporator End of Heat Pipe
Preliminary tests were performed on both heat pipes to determine the
minimum fluid change required for priming. This value was determined by
level priming tests, observing priming at Increasing Inventories until
repeatable priming occurred. The required Inventory was 120 cc which,
correcting for the additional length of the SEP heat pipes. Is approxi-
mately 20 percent less than the CTS Inventory.
3.6 PERFORMANCE TESTS ?
The heat pipes were Instrumented with 18 thermocouples, wrapped
with an electrical heater over a 38-Inch length and mounted over a
48-Inch length to a temperature-controlled baseplate using a grooved
condenser block with aluminum foil In all Interfaces. The test configu-
ration Is shown In Figure 7. Data were taken In the temperature range of
8S°F to 120°F. The results of tests with the 0. 070-1 nch-dlameter artery
heat pipe using 0.081-1nch-I.D. priming tubes are shown In Figure 8.
The solid points shown In the figure have been corrected using capacity
versus temperature results from tests on the 0.080-1nch-d1ameter artery
heat pipe. The dashed line Is the performance predicted by the
Multiwick program and can be seen to be In good agreement with the
measured values. The zero gravity prediction from the Hultiwick program
10
WATUNCH CAPACITY
corresponds to the result at 0.3-inch evaporator elevation. The fact
that the zero gravity prediction is lower than the earth gravity results
at no evaporator elevation is due in part to the contribution from
fillets and excess fluid natural reservoirs which aids significantly
the performance in one-g, but not in zero-g.
The capacity measured at 0.3-inch evaporator elevation was 245 watts.
As noted in Figure 8, the effective length of the test heat pipe was 72
inches which corresponds to 17,640 watt-inches. Sir.ce the effective
length of the heat pipe for actual SEP application is about 64 inches,
the capacity of the production SEP heat pipes would therefore be 2/5
watts. Also shown in the figure is the capacity of a single artery.
This result was obtained by raising the heat pipe until one artery was
observed to deprime and then applying a heat load.
Tests were also performed on the 0.070-inch-diameter artery heat
pipe containing gas in order to verify the effe-. *: of gas on priming and
capacity performance. At 0.32-inch and l.?3-incn evaporator elevations,
the capacity with gas was identical to that without gas. Priming was
consistent with or without gas. Figure 9 shows the temperature profiles
in the heat pipe at nearly off and fully on conditions. Data for the
0.080-inch-diameter artery heat pipe are shown in Figure 10. The capacity
at 0.30-inch evaporator elevation was 310 watts, which corresponds to
22,300 watt-inches. This capacity is 15 percent lower than Multi wick
prediction. The discrepancy is attributed to the impaired function of
one of the arteries. The fact that one of the arteries did not prime
reliably during priming tests seems to indicate that this artery sustained
some damage during heat pipe assembly. This heat pipe underwent X-ray
inspection but the source of the problem could not be identified.
A number of data points with one 0.080-inch-diameter artery primed
showed high capacity (14,000 watt-inches) at burnout. Groove dryout or
partial slab wick dryout was evident with only one artery primed. For
example, at 0,25-inch elevation, temperature gradients began to appear
in the evaporator at 160 watts, yet burnout (depriming of the artery)
did not occur until 210 watts were applied.
12
TEMKtATUK
The capacity as a function of vapor temperature was measured for
the 0.080-1nch>d1ameter pipe. The data shown In Figure 11 were used to
correct data taken at various adiabatic temperatures. Testing Is more
efficient timewise when the sink temperature Is fixed and power Is
Increased until burnout occurs. This results In burnout data at tempera
tures different from the design temperature of 122°F.
Figure 11. Capacity of 0.080-Inch Artery Heat Pipe as a
Function of Temperature
3.7 SUMMARY
The performance of both heat pipes substantially exceeded the 14,000
watt-inch capacity goal of this program; however, only the 0.070-1nch-
dlameter artery heat pipe with 0. 081 -Inch- I. D. priming caps showed
reliable artery priming. As a result, this design was selected for the
fabrication of six deliverable heat pipes during Phase II.
14
4. PHASE II DESCRIPTION
The objective of this phase of the program was to fabricate six
variable conductance heap pipes in a configuration suitable for inclusion
in a development SEP FM/PPU test article.
4.1 FINAL HEAT PIPE DESIGN
As recommended from the development activities in Phase I, a heat
pipe configuration with the 0.070-inch-diameter arteries and 0.081-inch-
I.D. priming tubes was selected for the fabrication of six deliverable
heat pipes. Detail drawings of the final design are shown in the Appendix.
The drawings include the changes made during Phase I, primarily regarding
the priming tube. The length of the evaporator was increased by 0.15
inch to allow the end cap weld to extend just beyond the end of the saddle
when the modules are assembled. An assembly drawing of the modules is
shown in SK78006 in the Appendix.
4.2 HEAT PIPE ASSEMBLY AND PROCESSING
All parts were cleaned per TRW procedure PR 2-28-1. The arteries
were subjected to bubble tests to establish the integrity of the mesh
screen and the priming tubes prior to installation of the arteries on the
slab wick. Subsequently, the completed slab wick/artery assemblies were
tested for priming reliability.
As a check of mechanical integrity and to identify any major leak,
each heat pipe was pressurized with nitrogen to 50 psig and held for 15
minutes. In addition, each heat pipe was leak checked with a vacuum leak
detector. No leaks were detected on any of the six heat pipes. Sub-
sequently, the heat pipes were vacuum bakeu at 275°F for 2 hours.
Identification numbers, 1 through 6, were scribed on the end caps of each
heat pipe.
4.3 LIQUID INVENTORY
Heat pipe number 3 (HP3) was selected for preliminary tests intended
to establish the minimum fluid inventory required for reliable artery
priming. Tests began with a 120 cc methanol inventory which was the one
used in the Phase I heat pipes. Reliable priming was found at 138 :c.
15
and to allow some tolerance, 140 cc were used for the other heat pipes.
This inventory is proportionally the same as the CTS heat pipe inventory,
correcting for increased length and larger artery diameter in the SEP
design.
4.4 PERFORMANCE TESTS
The heat pipes were installed on a temperature-controlled base plate
using 0.5-inch-thick grooved aluminum blocks with aluminum foil between
all interfaces to assure good thermal contact. The evaporator heater
was bonded to a grooved aluminum saddle which was bolted to the evaporator
section of the heat pipe. A sketch of the test configuration and mounting
details is shown in Figure 12. In this configuration, the effective length
of the heat pipes was approximately 66 inches. A minimum of six thermo-
couples were used; more in some tests.
Figure 12. Test Configuration
16
The general test procedure was to level the heat pipe to +^0.010
inch using a cathetometer, apply 25 watts, tilt the heat pipe to the
desired evaporator elevation and raise the power sequentially to 100
watts, 150 watts and 200 watts allowing 15 minutes to elapse between
power changes. Thereafter, the power was increased in 20-watt increments
until burnout occurred. In tests where the heat load exceeded 220
watts, some nonuniform evaporator temperatures were observed. These
nonuniformities were indications that part’ll groove dryout was occurring
in the evaporator without evidence of artery failure. The results of
tests on all heat pipes at 0.30-inch evaporator elevation and 120° +5°F
adiabatic temperature are summarized in Table 1. As shown, the capacity
of heat pipe number 6 is 150 watts, which is consistent with only one
Table 1. Test Resul ts-Evaporator Elevation 0.3 Inch,
Adiabatic Temperature = 120°F ,t5°F
(Effective Length of Pipes = 6t Inches)
Pipe
Number
Config-
uration
Power
Held
(Watts)
Power at
Groove
Dryout
(Watts)
Burnout
(Watts)
Comments
1
1
220
- —
230
138 cc inventory
2
2
270
310
None;
stopped
140 cc inventory
3
1
220
—
230
First pipe tested
138 cc inventory
4
1
220
260
None;
testing
stopped
at 300
watts
140 cc
5
2
280
290
300
140 cc
6*
2
>150
150
175
141 cc
7
2
300
220
320
140 cc
♦Performance below specification.
17
artery operating. Repeated attempts to prime both arteries were unsuccess-
ful. As a result, an additional heat pipe was fabricated and tested.
Tests results on this heat pipe are shown as pipe number 7 in Table 1.
Additional tests were performed on heat pipe number 5 to establish the
performance as a function of evaporator elevation, which is shown in
Figure 13. The data show no evidence of excess fluid contribution to the
capacity at 0.3-inch evaporator elevation, which is the one predicted in
zero gravity. The test configuration was modified to allow testing of
-6
HP5 loaded with 6 x 10” lb-moles of nitrogen gas. A cooling block was
installed on the gas reservoir and 0.25 inch of Teflon was inserted between
the condenser block and the temperature-controlled base plate. With the
reservoir temperature controlled between -90°F and -98®F, the heat pipe
turned on at 97°F and was full on at 118°F. The improved temperature
control range is attributed primarily to the larger reservoir- to-condenser
volume ratio resulting from the excess fluid reducing the vapor spaces in
the condenser section.
-p 20,000
- - 11,000 V
u
I
i
T
c
--»,ooo I
j- M,000
Figure 13. SEP Phase II “ Heat Pipe No. 5 Capacity
18
4.5 INDIVIDUAL HEAT PIPE SUMMARY
Six out of seven heat pipes met, and some of them substantially
exceeded, the 14,000-watt-inch capacity goal of this program.
Test results showed some differences in the performance between
heat pipes in terms of burnout capacity and capacity at which partial
groove dryout was observed. Differences in burnout capacity could be
the result of a reduction in cross section at some point in an artery-
possibly in the region of the 90-degree b^nd. Such a change in cross
section would reduce the capacity of the arteries due to increased
liquid flow resistance.
Differences in observed partial groove dryout could be due to
nonuniformities in the configuration of the grooves resulting from
variations in the tube inside diameter and/or wear of the threading
tool. This phenomenon, however, should not impact the performance of
the SEP heat pipe module since partial groove dry-out is observed only
at capacities higher than the designed operating capacities of the
SEP heat pipes.
4.6 MODULE ASSEMBLY
Two modules were assembled, each consisting of three heat pipes
soldered to two aluminum saddle halves supplied by NASA LeRC. An
assembly drawing of these modules, configurations A and B, are shown in
SK78006 in the Appendix. Heat pipes number 1, 2, and 4 were used in
module A. Module B used heat pipes 3, 5, and 7.
After the individual performance tests, the heat pipes were vacuum
dried, backfilled with nitrogen to 1 atmosphere and pinched off before
they were sent along with the saddles to an outside vendor for plating.
The specifications for tin plating the stainless steel tube sections and
the aluminum saddles are shown in SK77036-A and SK78011, respectively,
in the Appendix. A special fixture for assembling the modules was fab-
ricated. The fixture with a module at two different stages of assembly
is shown in Figures 14 and 15.
19
Figure 14. SEP Module Partially Assembled in Soldering Fixture
Figure 15. Assembled SEP Module Prior to Soldering
20
As shown in Figure 15, the saddles are spring loaded in order to
help alignment during soldering. A partial view of a module baseplate
after soldering is shown in Figure 16. The rectangular tubes extending
beyond the end of the baseplate were soldered to the saddle halves to
provide alternate cooling during ground tests of the SEP FM/PPU.
4.7 MODULE ACCEPTANCE TEST
The heat pipes of the assembled modules were individually tested.
The basic test configuration is sketched in Figure 17.
Four heater tapes, each 0.375 inch wide and 45 inches long, were
bonded to one side of the baseplate to provide nearly uniform heating
of the evaporator saddle. As one heat pipe was being tested, the other
two heat pipes were turned off by heating their gas reservoirs to '\^130°F.
The condenser section of the test heat pipe was clamped between two
2.5-inch x 1.5-inch grooved aluminum blocks. Aluminum foil was used in
all interfaces for good thermal contact. Heat dissipation from the
condenser block to ambient air by natural convection was sufficient to
allow steady-state operation of a heat pipe under a 220-watt heat load
at an adiabatic temperature of about 110°F. To test the performance at
hignar temperatures the condenser block was partially insulated. A
liqi'id-nitrogen-cooled block was mounted on the gas reservoir of the
test heat pipe.
i.velve thermocouples were used during the tests, located as shown in
Figure 17-
The three evaporator thermocouples were placed on the saddle directly
above the heat pipe being tested.
Prior to the test of a module, the fill tube was cut open and each
heat pipe was vacuum-leak checked, filled with 140 cc of spectral grade
methanol and loaded with 6 x 10"® lb-moles of 90 percent nitrogen - 10
percent helium gas. The procedure used to load a heat pipe with gas
consisted in filling a 133 cc reservoir with gas to 25 psia at room
temperature and then transferring gas into the heat pipe until a 7.2 psi
pressure drop was observed in the transfer reservoir.
21
oTSSSi
OUAUTY
Figure 16. Partial View of SEP Module After Soldering
Figure 17. SEP Module Test Configuration
22
The acceptance test procedure is outlined below;
1) Heat gas reservoirs (TCll and TC12) to 130° +^5°F.
2) Cool gas reservoir of test heat pipe (TCIO) to -102°
+5°F.
3) Raise evaporator end at least 3 Inches, relevel and
wal t 5 minutes.
4) Elevate evaporator 0.30 Inch and apply 220 watts.
5) Turn-on condition: TCI > 80°F when TC4-TC5 < b°F. Full
on condition; TCI > 1180F when TC4-TC8 s 5°F.
Tests on several heat pipes following the above acceptance test
procedure were unsuccessful. These heat pipes failed under loads
higher than 150 watts which is consistent with only one artery operating.
Reevaluation of X-iay data taken on the modules revealed the possible
cause of the priming problem. It was found that in the last few inches
of the evaporator section of the failed heat pipes the arteries were not
parallel to each other; i.e. , one artery was higher than the other in
the tube cross-section. The slab wick had apparently rotated in the pipe,
possibly during the clamping/soldering operation. This misalignment was
approximately 1/32 inch. A change in the test procedure was made in which
the heat pipes were required to prime with the evaporator 0.040 inch
lower than the condenser rather than being level. This change in the
test procedure was successful because in suloequent tests all the heat
pipes satisfied the acceptance criteria.
The turn-on and full-on temperatures of each heat pipe are shown in
Table 2.
As a final step in the processing of the heat pipes, each fill tube
was pinched off, welded and vacuum-leak tested.
The modules were delivered packed in individual wooden shipping
containers.
23
Table 2. Tum-on and Full-on Temperatures of SEP Heat Pipes
Module
guratlon
Heat Pipe
Number
Temperature (
Turn on
°F)
Full-on
A
1
103
123
2
103
121
4
105
126
B
3
100
124
5
100
125
7
105
126
24
5. SUMMARY AND CONCLUSIONS
TRW Defense and Space Systems Group has completed a two-phase program
under Contract NAS 3-21'TO for NASA Lewis Research Center in which two
variable conductance heat pipe modules were fabricated. Each module
contained three methancl/stainless steel heat pipes with individual
capacities in excess of 14,000 watt-inches at 50®C. A two-phase program
was undertaken co demonstrate, with development heat pipes, that the
design approach developed from earlier TRW Independent Research and
Development (I RAD) was sound.
During Phase I of the program a new heat pipe design was concei-'ed,
based on the results of 1974 and 1975 TRW IRAD programs. Two versions of
this design were built in configuration suitable for SEP application.
These prototypes were tested to confirm that changes in the design would
successfully resolve sporadic priming encountered during the IRAD programs.
Two heat pipes were fabricated, one using 0. 070-inch-diameter arteries,
and one using 0.080-inch-diameter arteries. The arteries ere placed in
the tube cross-section such that a 0. 040-inch gap existed between the
artery and the tube wall. The priming cap design consisted of a 0.00027-
inch stainless steel foil with a single row of 0.0067-inch holes spot
welded on the inside of a 0.75-inch-long stainless steel tube below a
window (,it in It. The inside diameter of this tube was 0.001 inch larger
than the inside diameter of the artery to which it was attached.
The gas reservoir was identical to the CTS design which yieldec
reservoi r-to-condenser volume ratio of approximately 1.
In addition, a technique was devised to splice the arteries in order
to accommodate the increased length (over 122 inches) of the StP heat
pipes.
Prior to the assembly of the two heat pipes, priming tests were
performed on both prototype arteries, the results leading to the utiliza-
tion of the 0.081-inch-I .D. priming tubes on the 0.070-inch-diameter
arteries in order to achieve reliable priming.
25
With a 120-cc methanol inventory, the capacities of the 0.070-inch-
diameter artery heat pipe and the 0.080-inch-diameter artery heat pipe at
0.30 inch evaporator elevation and 120°F adiabatic temperature were 17,600
watt-inches and 23,200 watt-inches, respectively. Although both heat pipes
substantially exceeded the capacity goal of 14,000 watt-inches, only the
0.070-inch-diameter artery heat pipe with 0.081-inch-I,D. priming tubes
showed reliable priming. As a result, this design was selected for the
fabrication of six deliverable heat pipes.
During Phase II of the program, seven heat pipes were fabricated and
tested. The methanol inventories of the SEP heat pipes was 138 +1 cc.
This inventory was determined from tests performed on a single heat pipe
to which fluid was gradually added until reliable priming was observed.
Acceptance tests were performed on all heat pipes, and six of seven met
the 220-watt capacity requirement. A selected heat pipe was loaded with
6 X 10"^ lb-moles of nitrogen gas to determine the effect of the gas on
the heat pipe capacity and establish its temperature control characteris-
tics. It was found that the presence of gas had no effect on capacity and
the temperature control of the heat pipe exceeded the design requirements
(turn on at 80°F and full on at 122°F). This heat pipe carried up to
300 watts (36 percent over the required 220 watts), although partial groove
dry-out was observed at high power levels.
The individual heat pipes were then emptied, back-filled with nitrogen
and pinch-weld closed. The evaporate-'' regions were tin plated and fused
prior to installation in two heat p<..> modules. Each module consists of
three heat pipes whose evaporator sections are soldered to two half-aluminum
saddles which form a baseplate.
After the module was soldered, the heat pipes were individually sub-
jected to acceptance tests. Each heat pipe was filled with 140 cc of
spectral grade methanol and loaded with 6 x 10"^ lb-moles of 90 percent
nitrogen - 10 percent helium gas.
The final acceptance test procedure consisted of leveling the heat
pipe to allow the arteries to prime, cooling the gas reservoir to -102°F,
elevating the evaporator end 0.30 inch and applying 220 watts. The heat
pipe was required to turn on at a tetuperature higher than 80°F and to be
26
fully on at a temperature higher than 118°F under the applied heat load.
Several heat pipes failed this acceptance test because one of their
arteries did not prime. During reevaluation of X-ray data taken on the
module, it was found that in the last few inches of the evaporator section
of the failed heat pipes the arteries were not parallel to each other;
i.e., one artery was higher than the other in the tube cross-section. The
slab wick had apparently rotated in the pipe, possibly during the clamping/
soldering operation. This misalignment was approximately 1/32 inch.
Tests were repeated in which the heat pipes were allowed to prime with
the evaporator end 0.040 inch lower than the condenser, and the results
were successful .
The six heat pipes turned on at temperatures higher than 100°F and
were fully on at temperatures higher than 121°F.
The improved temperature control range is attributed primarily to the
larger reservoir- to-condenser volume ratio resulting from the excess fluid
reducing the vapor spaces in the condenser section.
27
APPENDIX
DESIGN DRAWINGS
DRAWING NO.
77030 A
77031 A (1 of 2)
77031 A (2 of 2)
77032 A
77033
77034
77035
77036 B (1 of 3)
77036 {2 of 3)
77036 A (3 of 3)
77040
78006
78011
TITLE
TUBE AND PLUG, SEP HEAT PIPE
WICK ASSY, SEP HEAT PIPE
WICK ASSY, SEP HEAT PIPE
PRIMING TUBE ASSY. SEP HEAT PIPE
RESERVOIR WICKS, SEP HEAT PIPE
RESERVOIR, SEP HEAT PIPE
PRIMING FOIL
SEP HEAT PIPE ASSY. CONFIG. NO. 1
SEP HEAT PIPE ASSY.
SEP HEAT PIPE ASSY. CONFIG. NO. 2
ARTERY SPLICE TEST SAMPLE
SEP HEAT PIPE/BASEPLATE MODULE ASSEMBLY
SADDLE PLATING
PAGE BLANK fWT
A-1
REVISIONS
t
0 ^ ^
nm
CO
3
REVISiONS
6
REVISIONS
DATE APPROVED
ORIGINAL PAGE IS
OF POOR QUALITY
.030 T-Q c»vreg
. 0066 0 /A moles
PdlHItJ&p T-OtL Oe-TAlu.
toil.
35*y CiSFS^ .Qoozirnt ^OtL.
DFSCAfAnOM
MArpe»Au
IrrH
WO
BIGMEEVING SKETCH
•leWIATO*
0
PQlMfisK:^ ^OIL
COOL NXNT NQ
11982
INUT 1 OF
tVlTDM Ml « IV . I ». T «
A-8
,-9
hginm page «s
: POOR QUALITY
» T
m m
•.
•. If
5 •»
* i
£ 55
j “
> 3
14 <
a ;
«
0
•: f
u
o'
i :
“• 3
. »»
1
9 2
a
I
O
5.f
*00 H 03''
("St
1
1, Dooeufc
R
vy
I 4
. I
OfilQflVAL PAGE IS
OF POOR QUALITY
A-14
11982