The structural performance of a space station thermal energy storage (TES) canister subject to orbital solar flux variation and engine cold start up operating conditions was assessed. The impact of working fluid temperature and salt-void distribution on the canister structure are assessed. Both analytical and experimental studies were conducted to determine the temperature distribution of the canister. Subsequent finite element structural analyses of the canister were performed using both analytically and experimentally obtained temperatures. The Arrhenius creep law was incorporated into the procedure, using secondary creep data for the canister material, Haynes 188 alloy. The predicted cyclic creep strain accumulations at the hot spot were used to assess the structural performance of the canister. In addition, the structural performance of the canister based on the analytically determined temperature was compared with that based on the experimentally measured temperature data

Kerslake, T. W.

Thompson, R. L.

Tong, M. T.

English

NASA Technical Reports Server

N88-22406
STRUCTURAL ASSESSMENT OF A SPACE STATION SOLAR DYNAMIC HEAT
RECEIVER THERMAL ENERGY STORAGE CANISTER
R.L. Thompson, T.W. Kerslake,* and M.T. Tongt
Structural Mechanics Branch
NASA Lewis Research Center
ABSTRACT
Advanced analytical tools and experimental techniques were recently developed
in the Structural Mechanics Branch to assess the structural performance of a
space station thermal energy storage (TES) canister subjected to orbital solar
flux variation and cold startup operating conditions. Included in the assess-
ment were the impact of working fluid temperature and salt-void distribution
on the canister structure. Both analytical and experimental studies were con-
ducted to determine the temperature distribution in the canister. Subsequent
three-dimensional, nonlinear, finite-element, structural analyses of the canis-
ter were performed using both analytically and experimentally obtained tempera-
tures. For the lack of a better material constitutive model, the Arrhenius
creep law was incorporated into the procedure, using secondary creep data for
the canister material, Haynes-188 alloy. The predicted cyclic creep-strain
accumulatious at the hot spot were used to assess the structural performance of
the canister. Structural tests on a canister were also conducted. This was a
cooperative program with the Space Station Solar Dynamic Power Module Division,
Power Conversion and Heat Receiver Branch.
*Solar Oynamic Power Module Division, NASA Lewis Research Center.
_Sverdrup Technology, Inc., Lewis Research Center Group, NASA Lewis
Research Center.
2-281
https://ntrs.nasa.gov/search.jsp?R=19880013022 2020-03-20T06:31:11+00:00Z
SPACESTATIONCLOSEDBRAYTONCYCLESOLARDYNAMICPOWERMODULE
As part of the Phase II option of the space station, an additional p@wer
requirement of 50 kilowatts will be met by two high-efficiency solar dynamic
(SD) power modules. NASALewis Research Center ha_ chosen the Closed Brayton
Cycle (CBC) for the Space Station SDpower modules. The solar dynami_ modules
employ a concentrator to collect and focus incident solar flux onto the wall
of a cylindrical cavity-type heat receiver where it is converted to thermal
energy. A fraction of the thermal energy is transferred to a circulating work-
ing fluid to operate the heat engine and produce electrical power. The remain-
ing thermal energy melts a eutectic composition LiF-CaF2 salt in thermal energy
storag@ (TES) canisters integral with the receiver cavity. The salt stores and
releases thermal energy by undergoing phase changes at its melting point of
767 °C ([413 °F). This permits continuous operation of the Brayton hoat engine
during insulation and eclipse periods of the orbit. Shown are the solar
dynamic [_ower module and a cutaway of the solar receiver assembly.
_ ._r,,,_,_'_ _ - UNEAn ACTUATOR
/ _ STRUCTURE
_'__ "I ASSEMSLY
__1,/"_ _-'_sETA JOINT/ROlLRiNG
_- TRANSVERSEDOOM
I_vMAVOMIN6 FLUID TUBE_ \
MULTIFOIL _
'NSULATIOO- _._ _j._
W_N_ X 1 k
FLUIOOUT_
OUTLET_-'"" / y
MANIFOLD_-..._... "_
OVERALLDIMENsIONs
DIAMETER--IM rat
LENGTH--2'OScm
"-TUSE
SUPPORT
BAFFLE
r OWE
/ _u r,
/ __ APERTURE
_ _ APERTURE
ITfPJI_ PI.AT!
_ "x_ Lln'EM_.
W_T
STRUCTURE
(ALUMINUM)
CD.-68-32496
2-282
SPACE STATION THERMAL ENERGY STORAGE CANISTER
The space station orbit under consideration is a minimum insulation orbit. It
has a period of 91 minutes, with 37 minutes eclipse and a solar constant of
1323 w/m 2 (420 Btu/hr/ft2). During each orbital cycle, the canister is sub-
jected to appreciable transient thermal loads. Inelastic deformation can be
induced in localized regions leading to potential structural failure. Assess-
ment of durability requires reasonably accurate calculation of the structural
response under cyclic loading. This problem is an ideal case in which to
apply the recently developed analytical tools and procedures developed at NASA
Lewis.
The canister under consideration was located i143 nun (3.75 ft) behind the
receiver focal plane - the location believed to have the most severe thermal
environment. It is made of Haynes-188 alloy, and was designed by the NASA
Lewis Phase B Space Station contractor team of Rockwell International Rocket-
dyne Division and Garrett Corporation-AiResearch (Anon., 1986). The canister
under study is shown here.
I
I
PHASE ( f LI, _ ,,"_
CHANGE _ _"
CONTAINMENT _."" I'/
CANISTER ///
OUTER WALL -I
,-CONTAINMENT/
// CANISTER
/ SIDEWALL
/
I_.,.,,--WELDJOINT
/
--1--
25 _
_L
"_CONTAINMENT
CANISTER
INNER WALL
CD-88-32497
2-283
THERMAL ENERGY STORAGE CANISTER
A canister with the LiF-CaF 2 salt in its solidified state is shown here. The
void is approximately 25 percent of the total volume. As the solar flux heats
the salt, the salt liquefies and fills the canister volume. The liquefaction
process is extremely complex, particularly in a microgravity environment where
the surface tension induced flow phenomenon is the driving mechanism for con-
vection. Because the liquefaction process is not predictable, several worst-
case conditions were assumed in order to determine the structural performance
of the canister.
VOID
SOLI D SALT
'- CANISTER WALL
_EXPANDING LIQUID SALT
SOLAR FLUX
CD-88-32498
o o84
CANISTER-SALT CONFIGURATIONS FOR STEADY-STATE ANALYSES 
Because the exact salt formation in the canister under microgravity is not 
quantified, several different canister-salt configurations were analyzed to 
determine the effect of salt-void distribution on the canister structure. The 
configurations evaluated for the steady-state analyses are (a) canister filled 
with salt, (b) canister with an entrapped liquid pocket, (c) canister with cir- 
cumferential void at the canister outer-diameter wall, and (d) canister with 
void at the sidewall. These configurations are shown below. Three-dimensional 
finite-element thermal and structural analyses of the canister were performed 
using the MARC finite-element program (Anon., 1984). 
Subsequent nonlinear transient analyses were performed to obtain the cyclic 
stress-strain history for structural assessment of the canister. A canister- 
salt configuration with circumferential void at the outer-diameter wall was 
chosen for the transient analyses because steady-state analyses showed it to be 
the most severe case. A total of four transient analytical cases were studied 
to determine how the structural performance of the canister was affected by 
void in the canister, working fluid temperature, and cold startup operating 
condition. 
CANISTER FILLED WITH SALT CANISTER WITH LIQUID POCKET 
672 &NODE SOLID ELEMENTS 
936 NODES 
CANISTER WITH CIRCUMFERENTIAL VOID CANISTER WITH VOID AT SIDEWALL 
m-a6-32499 
ORBITAL SOLAR FLUX HISTORY FOR CANISTER TRANSIENT ANALYSES
Steady-state thermal boundary conditions were the maximum solar heat flux of
19.9 kw/m 2 (6300 Btu/hr/ft 2) distributed according to the canister projected
surface area, working fluid temperature of 704 =C (1300 °F), and thermal radia-
tion at the backwall. Based on these boundary conditions, metal temperatures
were predicted by using MARC and were then used in the structural analyses.
Determination of transient thermal loads was based on the transient orbital
heat flux shown below. Other transient thermal boundary conditions were the
working fluid temperature histories and backwall temperature histories. The
phase change of LiF-CaF 2 salt was also considered in the analyses. The calcu-
lated canister temperature histories were then used in the structural analyses
of the canister.
91-MINUTE MINIMUM ISOLATION ORBIT
HEAT FLUX,
KW/M2
20
10
0
-IC I I I
0 25 50 75
TIME, MIN
I
I00
CD-88-32500
,.'_-286
TYPICAL STEADY-STATE CANISTER TEMPERATURES AND STRESSES 
Typical steady-state temperatures and resulting stress distributions are shown 
for the case of a circumferential void at the canister outer diameter wall. 
The hot spot is at the point of maximum solar flux. 
location is 891 "C (1630 OF). The maximum Von Mises stress of 52 MPa (7568 
psi) occurs at the corners of the canister, as indicated in the figure. 
steady-state analyses showed that creep would be the predominant damage mode 
(ignoring oxidation and hot corrosion), an Arrhenius creep law was incorporated 
into the MARC code by means of a user subroutine. 
The temperature at this 
Since 
STEADY-STATE TEMPERATURE DISTRIBUTION TEMPERATURE, OF 
1600 
CANISTER WALL 7, 
VOID -- 
SALT -' / 
\ 
1550 
/ 
1500 
HOT SPOT 1-4 
STEADY -STATE STRESS D I STRl B UTI 0 N STRESS, ksi 1450-1k l l  
7 
6 
5 
4 
3 
2 
MAXIMUM STRESS LOCATIONS - 
2-287 
ORBITAL VARIATION OF MAXIMUM TEMPERATURE AND TOTAL CREEP STRAIN IN CANISTER 
Typical transient temperatures and resulting creep strains are shown for the 
case of a circumferential void at the canister outer-diameter wall. The tem- 
peratures and creep strains for the minimum insulation orbit are plotted at 
the location indicated on the figure. The working fluid temperature ranged 
from 980 to 1280 O F .  Using the predicted temperatures and strains, thermome- 
chanical tests on Haynes-188 specimens have been conducted to determine if the 
stress predictions are accurate and also to determine the effects of thermome- 
chanical cycling and possible ratcheting of the material. These tests, con- 
ducted in the NASA Lewis High Temperature Fatigue and Structures Facility, are 
unique to this effort. 
.loo 
.075 
TOTAL 
CREEP .050 
MICROSTRAIN 
.025 
0 1250 2500 3750 5000 
TIME; SEC 
1700 
1550 
TEMPERATURE, 
1400 "F 
1250 
1100 
CD-88-32502 
2-288 
ORIGINAL PAGE IS 
OF POOR QUALIW 
TEST APPARATUS AND INSTRUMENTED CANISTER 
Three canister test articles were used in the testing program. 
was instrumented with chromel-alumel thermocouples and radiation shields. The 
canisters were tested individually using a bench-top rig. 
was slip-fitted onto a Haynes-188 pipe and was enclosed in an insulated test 
chamber that provided a high-temperature environment representative of the heat 
receiver cavity. A solar simulator, consisting of high flux quartz lamps, was 
also enclosed in the test chamber to irradiate the bottom half of the canister 
exterior surface. The dual loop power controller was programmed to automati- 
cally produce the expected orbital heat flux variation for the minimum insula- 
tion orbit described above. Preheated air flow, which simulated the engine 
working fluid, provided the convective cooling to the canister interior sur- 
face. The experimental objectives were twofold: 
Each canister 
The test article 
1. to demonstrate the structural adequacy of the TES canister under sev- 
eral worst-case heating and salt configuration conditions. 
2. to determine canister temperature distributions in sufficient detail 
to support finite-element structural analyses for several known canister 
salt configurations. 
2-289 
CYCLICTHERMALRESULTS
Cold startup and cyclic tests were conducted to simulate the operation of the
canister under on-orbit receiver startup and orbital cyclic heat flux condi-
tions, respectively. The effect of salt distribution on canister temperature
profiles wasevaluated by testing canisters with three different salt configu-
rations. Cold startup canister tests were conducted by subjecting the test
article (at ambient temperature) to a step-input of maximumheat flux without
internal cooling airflow. This procedure was developed to simulate only the
first 15 to 30 minutes of the receiver startup cycle - the time period believed
to have the highest canister temperature gradients and highest canister salt
traction forces. Canister temperature response was measureduntil steady-state
conditions were approached (about 20 minutes). Cyclic canister tests were con-
ducted by subjecting the test article to a series of high-low step heat fluxes.
Cooling airflow rate and temperature were established at the beginning of each
test and held constant throughout the testing period (I0 simulated orbits or
about 15 hours). All three canisters were inspected before and after each test
for signs of deformation, cracks, or leaks. Inspection was performed nonde-
structively through the use of dye penetrant tests, x-ray radiography, and
visual inspection. Canister dimensions were also measured to quantify deforma-
tion. Typical measured temperatures for a cyclic run are shownfor four ther-
mocouple locations. These temperatures are in reasonably good agreement with
predicted temperatures.
THERMOCOUPLE LOCATION
1600
1500
TEMP,
oF 1400
1300
1200
170
GRAVITY A
-- 3rd CYCLE 1 @
- tl0HEAT FLUX
2/
@ I
190 210 230 250 270
TIME, MIN
CD-88-32504
2-290
SUMMARYOFSTEADY-STATEANALYSISRESULTS
Results of steady-state thermal and elastic structural analyses for the four
canister/salt configurations are summarizedbelow. Typical canister hot spot
and maximumstress locations were shownin an earlier figure. As expected, the
canister wall hot spot was located in the region of maximumheat input. The
maximumstress location was at the canister side wall outer diameter. Among
the four cases studied, the canister-salt configuration with circumferential
void at the outer-diameter wall had the highest stress level, 52 MPaat 891 °C
(7568 psi at 1635 °F). In all cases, however, the maximum stress level was
well below the yield strength of the Haynes-188 alloy, 262 MPa at 871 °C
(38000 psi at 1600 °F). This indicates an insignificant amount of material
plasticity. However, creep deformation could occur because of long-time expo-
sure to the receiver environment.
Analytical
case
Canister filled
with salt
Canister with
circumferential
void at O.D. wall
Canister with
entrapped liquid
salt pocket
Canister with void
at sidewall
Maximum temperature
oC oF
862 1583
891 1635
862 1583
868 1594
Maximum von Mises stress
MPa
40
52
41
42
psi
5823
7568
5976
6164
2-291
SUMMARYOFTRANSIENTANALYSISRESULTS
Results f[om the transient analyses are summarizedbelow. The accumulated
creep strain per cycle at the critical location (the hot spot, as noted ear -
lier) is the most crucial parameter to consider. This value is tabulated for
several different configurations of salt-void within the canister. For lack
of better knowledgeof the constitutive material properties of the Haynes-188
alloy, an Arrhenius steady-state creep law was used. As seen from the table,
the calculated creep strain is highly dependent upon the void configuration.
This dependencyarises because the void affects the heat conducted from the
canister wall to the salt and onto the working fluid. A void interferes with
the heat path, thus causing an increased thermal stress. This higher thermal
stress increases the resultant creep strain dramatically. Higher working fluid
temperatures also increase the calculated amount of creep strain per cycle.
The time required to accumulate one percent creep strain is also indicated in
the table.
Case
Canister filled with
salt, 527 to 693 °C
working fluid
tempe_ atare
CanisteJ: with
ci_cm_,L_=_=ntial void
at O.D. wall, 527 to
693 °C working fluid
temperature
Canister with
circumferential void
at O.D. wall, 613 to
697 °C working fluid
temperature
Canister with
circumferential void
at O.D. wall, engine
cold startup
Total accumulated creep
microstrain per cycle
0.0018
.0760
.1300
7.2500
Amount of time to
accumulate I percent
creep
960 years
23 years
13 years
0.24 years
or
1400 cycles
2-292
SUMMARYOFRESULTSANDCONCLUSIONS
The creep-failure criteria had not been defined for the canister. Preliminary
NASALewis in-house testing of the Haynes-188alloy has shownthat it behaved
in a significantly different mannerunder thermal cyclic loading than under
isothermal loading. The design data available for the Haynes-188alloy are
based on monotonic and isothermal loadings. Becauseof this, further tests
and analyses are in progress at NASALewis to determine the behavior of the
Haynes-188alloy under thermal cyclic loading. In addition, long-term testing
of the canister is being planned. The results from these programs should ena-
ble more refined analyses and further improve the design of the canister that
will be subjected to repetitive orbital thermal loadings.
The structural performance of a space station TES canister was evaluated ana-
lytically and experimentally at various operating conditions. Creep-strain
results from structural analyses were used for the structural assessment. The
major results of this study are as follows:
i. Creep rupture will most likely be the predominant failure mode for the
TES canister (ignoring oxidation and hot corrosion), according to the can-
ister operating thermal environment information provided.
2. Structural performance of the TES canister is sensitive to the salt-
void distribution inside the canister. This is because of the higher peak
temperature and stress levels caused by the exact location of the void.
3. Structural performance of the TES canister is sensitive to the thermal
environment because creep depends strongly on temperature. Working fluid
tempe_,t_ire also hab a significant effect on the structural performance of
the canister.
4. The existence of a liquid salt pocket inside the canister has no sig-
nificant effect on the structural performance of the canister because the
LiF-CaF 2 salt has a much lower modulus than the Haynes-188 alloy.
5. Additional thermal cyclic testing of Haynes-188 specimens and canis-
ters must be conducted before creep-failure criteria can be defined for
the canister.
6. Advanced analytical tools and experimental techniques have been suc-
cessfully demonstrated for this application.
2-293
REFERENCES
Anon., 1986, MARC General Purpose Finite Element Program, MARC Analysis
Research Corporation, Palo Alto, California.
Anon., 1984, Space Station WP-04 Power System Preliminary Analysis and Design
Document, DR02.NAS 3-24666, June 1986, Vol. I, Section 2, pp. 240-267.
Ellis, J.R., Bartolotta, P.A., and Mladsi, S.W., 1987, "Preliminary Study of
Creep Thresholds and Thermomechanical Response in Haynes 188 at Tempera-
tures in the Range 649 C to 871C," Proceedings of the Conference on
Turbine Engine Hot Section Technology, NASA CP-2493, pp. 317-334 (FEDD doc-
ument, available to general public after October 1989).
2-294


Structural assessment of a space station solar dynamic heat receiver thermal energy storage canister

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