thermal energy storage experiments leaflet

Thermal Energy Storage Experiments

COMPLEX AUTONOMOUS

PAYLOAD

STS-69 ENDEAVOR

CAPL-2/GVA 1995

Thermal energy storage (TES) payload.

Sponsored By Office of Space Access and Technology

iDEPOStTORY UMR\M\

I

National Aeronautics and Space Administration Lewis Research Center Space Flight Systems Directorate Space Experiments Division

0830-C

INTRODUCTION

The Thermal Energy Storage (TES) experiments are designed to provide data for understanding the long-duration micro-gravity behavior of thermal energy storage f luor ide salts that undergo repeated melt ing and freezing. Such data have never been obtained before and have direct appl ication to using on-orbit solar dynamic power systems. These power systems wil l store solar energy in a thermal energy salt such as l i thium fluoride calcium dif luoride (LiF-CaF2). The energy is stored as the latent heat of fusion when the salt is mel ted by absorbing solar thermal energy. The stored energy is extracted dur ing the shade port ion of the orbit. This enables the solar dynamic power system to provide constant electrical power over the entire orbit.

The principal investigator of the TES experiments was Carol Tolbert of the Power Techno logy Div is ion at NASA Lewis Research Center, Cleveland, Ohio . Project management for the exper iment was performed by Frank Robinson, Jr. of the Space Experiments Division. Task work was accompl ished by an in-house dedicated project team consisting of NASA Lewis and N Y M A Technology, Inc., engineers and technicians. The project was supported by the NASA Headquarters Off ice of Space Access and Technology.

BACKGROUND

Future space appl icat ion of an advanced power system in sun-shade operat ing condit ions requires the system to have high efficiency, reliability, low specific weight, and low life-cycle cost. Advanced technology work is helping to establish a solar dynamic power system for use in Earth-orbi t ing spacecraft. This system cont inuously provides electrical power by collecting and storing solar thermal energy that is later converted to electrical power whi le in the Earth's shadow. The col lected solar thermal energy is stored in a heat receiver that consists of many canisters. Each canister holds a f luoride salt (LiF-CaF 2 ) wh ich is melted by absorbing the solar thermal energy f rom the Sun. W h e n

the salt is melted, it expands approximately 30 percent in vo lume. The stored thermal energy is released when the salt shrinks or freezes dur ing the shade port ion of the orbit. The repeated melt ing and freezing of the salt creates voids in the salt dur ing solidif ication. Vo id format ion wi th in the salt impacts the heat transfer rate to the salt and the design of the heat receiver containers holding the TES salt. Consequently, understanding and predict ing the melt-and-freeze behavior of the contained TES f luoride salt in the on-orbit microgravity environment is essential for achieving an improved design for heat receivers of solar dynamic power systems.

Dr. David Jacqmin of the NASA Lewis Research Center has developed and is refining a computer code TESSIM (Thermal Energy Storage Simulation). TESSIM can predict the behavior and migrat ion of voids in the receiver canisters. It is currently useful as a qualitative design tool but requires further experimental val idation. Once thoroughly val idated, the code wil l be invaluable in the detailed design of lighter, more efficient solar dynamic receivers.

The first Thermal Energy Storage experiment (TES-1) was successfully f lown on STS-62 in March 1994. The results of TES-1 test data are preliminary but agree in general wi th the TESSIM predictions. The TES-1 canister was examined nondestruct ively by using a technique called "tomography/'computer-assisted radiographic images. Images of the phase change material inside the annular vo lume were developed. The images showed that melt ing and freezing of the phase change material (PCM) caused significant shifting of the mass during a cycle. In general, TESSIM appears to have predicted vo id behavior accurately as is evidenced by compar ing the tomographic images wi th the TESSIM images. These initial results f rom TES-1 of high-temperature TES melt ing and freezing under microgravity do not absolutely validate TESSIM, but the compar ison of the predictions wi th data establishes a basic conf idence in the code. Future experiments such as TES-2, 3 and 4 wil l contr ibute to further val idat ion of TESSIM.

PROJECT OBJECTIVE

The object ive of this flight project work is to develop and flight-test long-duration microgravity experiments for obtaining data that characterize the void behavior in TES f luoride salts. This project is the first in which TES materials wil l be subjected to an extended microgravity durat ion whi le changing phase.

EXPERIMENTAL APPROACH

The first two separate fl ight experiments, TES-1 and TES-2, have been developed to obtain data on salt behavior in cylindrical canisters. The TES-1 exper iment was successfully f lown as part of the OAST-2 Hitchhiker payload on the Columbia Shuttle STS-62 in early 1994. Experiment TES-2 wil l be part of the C A P L - 2 / G V A payload on the Endeavor Shuttle STS-69 mission in July 1995. The TES-1 and TES-2 experiments are identical except for the f luoride salts to be characterized. Both experiments use a sealed cylindrical Haynes-188 canister to hold the salts. The first experiment, TES-1, provided data on l i thium f luoride (LiF) which melts at 1121 K. The second experiment, TES-2, wi l l provide data on a f luoride eutectic (LiF/CaF 2) wh ich melts at 1042 K. Each experiment is a complex autonomous payload in a Get-Away-Special (GAS) payload canister. Hence, no power is required f rom the shuttle. Flight data are stored in the random access memory of each payload. A postflight CAT scan of each TES salt container wil l provide data on void sizes and distr ibution. Later, two addit ional experiments, TES-3 and TES-4, wil l be developed for obtaining data on salt behavior in wedge-shaped canisters.

FLIGHT HARDWARE

The TES-2 experiment is mounted along wi th other experiments on a gas bridge which is placed wi th in the payload bay of the shuttle. Each TES exper iment occupies 5 f t 3 and weighs about 245 lb prior to placement in the GAS payload container.

Each experiment payload consists of the same three hardware subsystems (fig.1). The top section or the exper iment section (fig. 2) is made up of a cylindrical canister assembly, a two-zone radiant heater, high-temperature multi layer insulation (MLI), and an MLI shutter and drive mechanism as wel l as temperature measurement instrumentat ion. Temperature is measured at many different locations wi th swaged 20-mil, type K thermocouples. The entire canister assembly is enclosed wi th in the

MLI andMLI shutter. The primary components of the canister assembly are the Haynes-188 canister and the thermal radiator disc. Each canister has an annular cross section created by a solid conductor rod along the axis of each canister. The annular cylindrical volume contains the TES salt. The canisters are welded closed in a vacuum after the salt is loaded into the canister.

The middle section is occupied by the data acquisit ion and control system (DACS). Also, independent high-temperature control units are located in the middle section. They provide added control for maintaining a safe maximum temperature level associated wi th these 1200-K temperature level experiments.

Finally, the bo t tom section consists of a battery box that contains 23 silver-zinc

PROGRAM HIGHLIGHTS

• First long-term (10 hr) microgravity thermal energy storage experiments per formed in space.

• First high-temperature (1042 K) experiments that cyclically melt and freeze Li-based salts.

• Sof tware con t ro l logic and data acquisit ion designed for operat ional contingencies to help assure mission success.

• A u t o n o m o u s operat ion of experiments achieved by self-contained battery cells.

POINTS OF CONTACT

Principal Investigator Carol M. Tolbert NASA Lewis Research Center Power Technology Division Cleveland, O H 44135 (216) 4 3 3 - 6 1 6 7

Flight Project Manager Frank Robinson, jr. NASA Lewis Research Center Space Experiments Division Cleveland, O H 44135 (216) 4 3 3 - 2 3 4 0

Program Manager Richard Gualdoni NASA Headquarters Off ice of Space Access

and Technology Washington, DC 20546 ( 2 0 2 ) 3 5 8 - 4 6 6 9

CAPL-2/GVA Mission Manager Christopher Dunker Goddard Space Flight Center Greenbelt , M D 20771 (301) 2 8 6 - 4 2 7 1

Figure l.—TES payload.


The middle section is occupied by the data acquisition and control system (DACS). Also, independent high-temperature control units are located in the middle section. They provide added control for maintaining a safe maximum temperature level associated wi th these 1200-K temperature level experiments.


cells which provide all the electrical energy required for the two-zone radiant heater and the DACS. Each cell contains a potassium hydroxide electrolyte. The initial electrical energy level provided by the battery box for each payload prior to placement in the shuttle is about 6300 W h , which accounts for any battery degradation over t ime. The energy expected to be used on-orbit by each exper iment is about 3400 W h .

Thermal energy needed to melt the TES salt in each canister is provided by a two-zone radiant heater. The cylindrical heater material consists of boron nitride wi th a graphite conduct ive path. Two radiant heater zones create a temperature difference in the salt wh ich causes void movement in the TES salt. The void movement is f rom its initial location toward the high-temperature zone of the heater.

COMPLEX AUTONOMOUS

PAYLOAD

STS-69 ENDEAVOR

CAPL-2/GVA 1995

FLIGHT HARDWARE

The TES-2 experiment is mounted along with other experiments on a gas bridge which is placed wi th in the payload bay of the shuttle. Each TES experiment occupies 5 f t 3 and weighs about 245 lb prior to placement in the GAS payload container.

Each experiment payload consists of the same three hardware subsystems (fig.1). The top section or the exper iment section (fig. 2) is made up of a cylindrical canister assembly, a two-zone radiant heater, high-temperature multi layer insulation (MLI), and an MLI shutter and drive mechanism as wel l as temperature measurement instrumentat ion. Temperature is measured at many different locations wi th swaged 20-mil, type K thermocouples. The entire canister assembly is enclosed wi th in the

MLI andMLI shutter. The primary components of the canister assembly are the Haynes-188 canister and the thermal radiator disc. Each canister has an annular cross section created by a solid conductor rod along the axis of each canister. The annular cylindrical volume contains theTES salt. The canisters are welded closed in a vacuum after the salt is loaded into the canister.



cells wh ich provide all the electrical energy required for the two-zone radiant heater and the DACS. Each cell contains a potassium hydroxide electrolyte. The initial electrical energy level prov ided by the battery box for each payload prior to placement in the shuttle is about 6300 W h , wh ich accounts for any battery degradation over t ime. The energy expected to be used on-orbit by each exper iment is about 3400 W h .

Thermal energy needed to melt the TES salt in each canister is prov ided by a two-zone radiant heater. The cylindrical heater material consists of boron nitr ide w i th a graphite conduct ive path. Two radiant heater zones create a temperature difference in the salt wh ich causes vo id movement in the TES salt. The vo id movement is f rom its initial location toward the high-temperature zone of the heater.

— Experiment sect ion

Data acquisi t ion and control system (DACS)

Battery vent Payload vent

Battery box

Figure h—TES payload.

I




cells which provide all the electrical energy required for the two-zone radiant heater and the DACS. Each cell contains a potassium hydroxide electrolyte. The initial electrical energy level provided by the battery box for each payload prior to placement in the shuttle is about 6300 W h , which accounts for any battery degradation over t ime. The energy expected to be used on-orbit by each exper iment is about 3400 W h .

Thermal energy needed to melt the TES salt in each canister is provided by a two-zone radiant heater. The cylindrical heater material consists of boron nitride w i th a graphite conduct ive path. Two radiant heater zones create a temperature difference in the salt which causes void movement in the TES salt. The void movement is f rom its initial location toward the high-temperature zone of the heater.

-—Exper iment sect ion

- Battery box

- Payload vent

COMPLEX AUTONOMOUS

PAYLOAD

STS-69 ENDEAVOR

CAPL-2/GVA 1995

Figure l.—TES payload.

Heater power levels and MLI shutter opening and closing are control led by the DACS located in the middle section of the payload. The DACS not only controls the thermal cycl ing of the experiment, but also periodically records the instrumentat ion output signals. An 80386SX central processing unit is used in the DACS to provide the needed data col lect ion speed and processing.

OPERATION SEQUENCE

The TES experiments are activated by an astronaut w h o begins a 5-hr heatup phase for each experiment. A vacuum environment exists in the GAS payload containers. After the heatup phase to a TES salt melt is comple ted, the on-orbit melt-and-freeze thermal cycles begin. A total of four thermal cycles over a 10-hr per iod are planned for characterizing the behavior of theTES salts in a 10" 3 -genvironment. O n e thermal cycle consists of a melt phase and a freeze phase each of which takes about 60 min.

The freeze or solidif ication phase of a thermal cycle is initiated when heater power is turned off and the MLI shutter is opened . Thermal energy dissipat ion needed to cause the salt to freeze is achieved by conduct ing the thermal energy out of the salt into the solid rod in the center of the canister, and f rom the rod to the thermal radiator disc. The disc radiates the stored thermal energy (latent heat of fusion for the salt) to the GAS payload container upper end-plate. This plate in turn radiates the thermal energy out to space. A t the end of the freeze phase, the MLI shutter is then closed and the next melt cycle begins.

MLI shutter door (one of two) V N

Heater - MLI

Support-

Figure 2—TES experiment section.

Flight data are recorded at 5-min intervals and primarily consist of the t ime variation of temperatures and heater power dur ing the heatup, melt-and-freeze, and coo l -down phases of the experiment. Other data include the t ime elapsed from the startup of the experiment, t ime of each data sample, power level, and estimated electrical energy remaining in the battery cells. After the thermal cycles are completed and the exper iment section cools d o w n to approximately 750 K, the experiments are deactivated by an astronaut. At this point, a vent valve in each of the GAS payload containers is closed to seal off the GAS containers prior to a shuttle de-orbit.

B-0686-A April 95

Conductor r o d ^

TES material Danister

Canister

Radiator

Conductor rod

thermal energy storage experiments leaflet

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