Selection of High Temperature Thermal Energy Storage Materials for

~ _ _ ~ ~ ~ ~ _ - ~ ~ ~ ~ ~ - -

. . NASA Technical Memorandum 89886

Selection of High Temperature Thermal Energy Storage Materials for Advanced Solar Dynamic Space Power Systems

4EASA-TW-89866) SBLECTICb O € LIGb ~ a 7 - 2 2 134 3 E B P E O A T U R E T6BbIAL E N E R G Y S I C G A G E MATERIALS €C3 A D V A N C E D S C L A R D P L A B I C SEACE EOUEB SYSTEHS (NASA) 13 p Avail: h I l S EiC Unclas &02/ME A01 C S C L 10B G.?/34 0074241

Dovie E. Lacy, Carolyn Coles-Hamilton, and Albert Juhasz Lewis Research Center Cleveland, Ohio

9 Prepared for the 22nd Intersociety Energy Conversion Engineering Conference cosponsored by the AIAA, ANS, ASME, SAE, IEEE, ACS, and AIChE Philadelphia, Pennsylvania, August 10- 14, 1987

I

https://ntrs.nasa.gov/search.jsp?R=19870012741 2018-12-25T08:59:34+00:00Z

ERRATA

NASA Techn ica l Memorandum 89886

SELECTION OF H I G H TEMPERATURE THERMAL ENERGY STORAGE MATERIALS FOR ADVANCED SOLAR DYNAMIC SPACE POWER SYSTEMS

Dov ie E. Lacy, C a r o l y n Coles-Hamil ton, and A l b e r t Juhasz August 1987

Page 3, r e f e r e n c e 1 : T i t l e shou ld read, " Impact of Thermal Energy S to rage P r o p e r t i e s on S o l a r Dynamic Space Power Convers ion System Mass,".

Page 4 , r e f e r e n c e 7 , l i n e 2: P r o p e r t i r e s shou ld be P r o p e r t i e s .

SELECTION OF H I G H TEMPERATURE THERMAL ENERGY STORAGE MATERIALS FOR ADVANCED SOLAR DYNAMIC SPACE POWER SYSTEMS

Dovie E. Lacy, Carolyn Coles-Hamilton, and A l b e r t Juhasz Na t iona l Aeronautics and Space Admin i s t ra t i on

Lewis Research Center Cleveland, Ohio 44135

Abs t rac t

Under t h e d i r e c t i o n o f NASA's O f f i c e o f Aeronaut ics and Space Technology (OAST), t h e NASA Lewis Research Center has i n i t i a t e d an in-house thermal energy s torage program t o i d e n t i f y com- b i n a t i o n s o f phase change thermal energy s torage media f o r use w i t h a Brayton and S t i r l i n g advanced s o l a r dynamic (ASD) space power systems operat ing between 1070 and 1400 K. A s tudy has been i n i t i - a ted t o determine s u i t a b l e combinations o f thermal energy s torage (TES) phase change m a t e r i a l s (PCM) t h a t r e s u l t i n t h e smal lest and l i g h t e s t weight ASD power system poss ib le . To date t h e heats o f f u s i o n o f severa l f l u o r i d e s a l t m ix tu res w i t h m e l t i n g p o i n t s g rea te r t han 1025 K have been v e r i - f i e d exper imenta l ly . The s tudy has i n d i c a t e d t h a t these s a l t systems produce l a r g e ASD systems because o f t h e i r i nhe ren t low thermal c o n d u c t i v i t y and low dens i t y . I t i s d e s i r a b l e t o have PCMs w i t h h i g h d e n s i t i e s and h igh thermal c o n d u c t i v i t i e s . Therefore, a l t e r n a t e phase change m a t e r i a l s based on m e t a l l i c a l l o y systems are a l s o being considered as p o s s i b l e (TES) candidates f o r f u t u r e ASD space power systems.

I n t r o d u c t i o n

So la r dynamic systems are a c t i v e l y being s t u d i e d as a means o f p r o v i d i n g heat and e l e c t r i - c a l power f o r space app l i ca t i ons . Advanced Solar Dynamic (ASD) power systems o f f e r t h e p o t e n t i a l f o r e f f i c i e n t , l i gh twe igh t , r e l a t i v e l y compact and long - l i ved space power systems app l i cab le t o a wide range o f power l e v e l s ( 3 t o 300 kWe), and a wide v a r i e t y o f o r b i t s . Thermal energy storage (TES) w i l l be requ i red by these ASD power systems t o p rov ide power t o t h e heat engine d u r i n g s o l a r ec l i pse . The l a t e n t heat TES concept t h a t w i l l be discussed i n t h i s paper r e s u l t s f rom a s o l i d t o l i q u i d phase change which o f f e r s a l i g h t w e i g h t and d i r e c t method o f p r o v i d i n g t h e heat engine w i t h a un i fo rm heat source. While many c r i t i c a l technology issues e x i s t f o r ASD power systems, f i n d i n g an e f f i c i e n t means o f energy s torage i s p r e s e n t l y t h e l e a s t w e l l de f i ned and understood. Under t h e d i r e c t i o n o f NASA's O f f i c e o f Aeronau- t i c s and Space Technology (OAST), NASA Lewis has i n i t i a t e d an advanced s o l a r dynamic t e s t i n g and development program. The goals o f t h i s in-house program a r e t o i d e n t i f y and s e l e c t h igh temper- a t u r e (1025 t o 1400 K ) phase change thermal energy s torage m a t e r i a l s which w i l l y i e l d l i g h t weight, compact and e f f i c i e n t s o l a r dynamic Brayton and S t i r l i n g space power systems w i t h an opera t i ona l l i f e o f 7 t o 10 yr.

L i t e r a t u r e surveys and a n a l y t i c a l screening has been performed t o i d e n t i f y PCM systems w i t h heats o f f u s i o n g rea te r t han 400 kJ/kg. Compar- i sons have been made between s a l t and m e t a l l i c PCM systems and i t was found t h a t t h e m e t a l l i c PCMs produced t h e sma l les t and l i g h t e s t weight

ASD systems because o f t h e i r h i g h e r thermal con- d u c t i v i t i e s and dens i t i es . T h i s paper w i l l d e t a i l t h e methods used t o i d e n t i f y and s e l e c t candidate PCMs f o r advanced s o l a r dynamic space power systems. Also, t h e e f f e c t s o f PCM s e l e c t i o n on a 35 kWe Closed Brayton Cycle (CBC) and a Free P i s t o n S t i r l i n g Engine (FPSE) power system w i l l be discussed.

A n a l y t i c a l Screening

The p r imary focus o f t h e i n house "Advanced So la r Dynamic Systems Code," i s t o determine t h e impact o f t h e thermophysical p r o p e r t i e s o f t h e se lec ted PCMs on t h e power convers ion systems (PCS) mass and performance. Although, s e l e c t i o n o f PCMs w i t h h i g h m e l t i n g p o i n t s w i l l increase t h e system e f f i c i e n c y o f a S t i r l i n g o r Brayton power system, t h e system mass was found t o a l s o be sen- s i t i v e t o o t h e r thermophysical p r o p e r t i e s o f t h e PCM. The computer systems code used i n t h i s s tudy w i l l g i v e t h e minimum system mass f o r a Brayton and S t i r l i n g power sys em opera t i ng a t t h e m e l t i n g p o i n t o f va r ious PCM5.l The goal o f t h e systems e f f o r t i s t o i d e n t i f y systems w i t h s p e c i f i c weights l e s s than 60 kg/kWe f o r LEO based se rv i ce .

Receiver Considerat ions

As shown i n F ig . 1, t h e heat r e c e i v e r c o n t r i - butes g r e a t l y t o the mass of a s o l a r dynamic power system. A t y p i c a l s o l a r dynamic heat r e c e i v e r i s shown i n F ig . 2(a) and a d e t a i l o f one PCMlworking f l u i d tube i s shown i n F ig . 2 ( b ) . The study was done us ing th ree s a l t based PCMs (L iF, LiF-CaF2, NaF) and two m e t a l l i c PCMs (Mg-Si and Ge) se lec ted f rom t h e i n i t i a l l i t e r a t u r e survey. F igs. 3 and 4 show t h e system masses of a 35 kWe Brayton and a 35 kWe S t i r l i n g PCS us ing bo th s a l t and metal PCMs. One c r i t i c a l d i f f e r e n c e i n t h e masses o f t h e s a l t and metal systems i s t h e s i z i n g o f t h e heat r e c e i w r c a v i t y . It i s d e s i r a b l e t o have u n i f o r m f l u x d i s t r i b u t i o n w i t h i n t h e c a v i t y . t h e r e c e i v e r was s ized by t h e diameter and spacing o f t h e s torage tubes based on a reasonable maximum al lowable f l u x . i t i e s was used i n t h e analys is .

Therefore,

The l a r g e r r e c e i v e r o f bo th cav-

One c h a r a c t e r i s t i c o f s a l t PCMs i s low t h e r - mal c o n d u c t i v i t y w h i l e t h e m e t a l l i c s a re ve ry good conductors. Because o f t h e h i g h thermal conduct- i v i t i e s o f t he metal PCMs, h ighe r s o l a r f l u x e s can be t o l e r a t e d w i t h i n t h e c a v i t y r e s u l t i n g i n a sma l le r heat rece ive r , see Fig. 5(a) . To improve t h e thermal c o n d u c t i v i t y of t h e s a l t system f i n s and r e f l e c t o r s are r e q u i r e d t o evenly d i s t r i b u t e t h e s o l a r f l u x w i t h i n t h e c a v i t y , t h i s produces a l a r g e and massive heat rece ive r , see F ig . 5(b).

ponents a re d i r e c t l y a f f e c t e d by an increase and o r decrease i n t h e d e n s i t y and heat of f u s i o n o f t h e PCM. For example, i f t h e d e n s i t y were

The mass o f severa l o f t h e heat r e c e i v e r com-

1

decreased more containment m a t e r i a l would be r e q u i r e d and t h e weight o f t h e support s t r u c t u r e and t h e o u t l e t manifold would increase. Moreover, i f t h e heat o f f us ion i s increased t h e amount o f s torage m a t e r i a l requi red w i l l decrease thus decreasing t h e rece ive r mass. be l o g i c a l t o assume t h a t i n order t o minimize t h e r e c e i v e r weight, a PCM w i t h a h i g h d e n s i t y and h i g h heat o f fus ion o r a combination o f PCMs w i t h heat o f f u s i o n values h i g h enough t o o f f s e t t h e mass p e n a l t y imposed by low d e n s i t y values must be se lected.

Therefore i t may

Systems Computer Code

The computer code used i n t h i s s tudy deter- mines f o r a g i ven peak c y c l e temperature t h e o p t i - mum temperature r a t i o t h a t w i l l g i v e t h e minimum system mass f o r t h e S t i r l i n g and Brayton power systems. Moreover, the ana lys i s f o r t h e Brayton power system f u r t h e r opt imizes t o g i v e t h e pres- sure r a t i o a t t h e minimum mass cond i t i ons . Several assumptions were made i n generat ing t h e mass models f o r t h e Brayton and S t i r l i n g (PCS) and t h e PCMs. Namely, steady s t a t e performance o f b o t h o f these systems was assumed. assumed a l l o f t h e heat which i s absorbed by t h e PCM i s t r a n s f e r r e d t o t h e PCS working f l u i d . s p e c i f i c mass o f t h e concentrator and heat 3 i p e r a d i a t o r were assumed t o be 1.22 and 5 kg/m r e s p e c t i v e l y . assumed t o be 0.88.

A n a l y t i c a l Resu l t s

I t was a l so

The

The e m i s s i v i t y o f t h e r a d i a t o r was

To determine the ef fects o f a PCM's heat o f f u s i o n and d e n s i t y on t h e mass o f a S t i r l i n g PCS, a parametr ic s tudy was done. I n t h i s study, t h e d e n s i t y and heat o f f us ion o f L i F was used t o assess t h e mass pena l t i es associated w i t h va ry ing these thermophysical p r o p e r t i e s over a s p e c i f i e d temperature range. F i r s t , t h e heat o f f u s i o n was v a r i e d over a range o f 400 t o 1200 kJ /kg w i t h t h e d e n s i t y be ing h e l d constant a t 1874 kg/m3. As shown i n F ig . 6, t h e system mass decreases w i t h i nc reas ing heats of f us ion evaluated a t a constant dens i t y . S i m i l a r l y , the system mass decreases w i t h i nc reas ing densi ty when evaluated us ing a s p e c i f i e d heat of fus ion (F ig . 7 ) . f i g u r e s , i t should be noted t h a t t h e r a t e o f change i n system mass i s l ess a t t h e h ighe r heats o f f u s i o n and dens i t i es .

I n both

F i g u r e 8 shows d i f f e r e n t scenarios o f t h e same system evaluated us ing combinations o f PCMs w i t h low, medium, and h igh d e n s i t i e s w i t h h i g h and low heats o f fus ion. Using mass as t h e s e l e c t i o n c r i t e r i o n , i t i s evident t h a t t h e system w i t h t h e low d e n s i t y and low heat o f f u s i o n has a h igh mass. Moreover, t h e system w i t h h i g h heat o f f us ion and d e n s i t y i s t he l e a s t massive. The f i g u r e a l s o i n d i c a t e s t h a t t he re are combinations o f t h e heats of fusion and t h e d e n s i t y where t h e system mass i s p r a c t i c a l l y t h e same. Therefore, one o f t h e key factors t h a t w i l l l i m i t t h e a b i l i t y t o i d e n t i f y systems wi th l o w masses i s t h e selec- t i o n o f PCMs w i t h high heats o f f u s i o n and d e n s i t i e s o r w i t h t h e r i g h t combinations o f thermophysical p r o p e r t i e s such as thermal c o n d u c t i v i t y .

s t a n t i a l when se lec t i ng PCM systems w i t h both h i g h d e n s i t y and h i g h heats o f f us ion . F i g u r e 9 shows t h a t s i g n i f i c a n t weight r e d u c t i o n can be achieved by us ing t h e ASD systems over t h e s t a t e o f t h e a r t

Mass savings of a power system can be sub-

2

(SOA) systems and Space S t a t i o n Technology.2 To d a t e L i F has been i d e n t i f i e d as t h e best s a l t system f o r achiev ing a l i g h t w e i g h t system because o f i t s h i g h heat o f f us ion . Yet, t h i s s tudy i n d i c a t e s t h a t meta l systems produce l i g h t w e i g h t AS0 systems because o f t h e h ighe r thermal conduct- i v i t i e s and h igh dens i t i es .

Although t h e p r e l i m i n a r y ana lys i s o f these systems appear promising, t h e i ssue o f t r a n s f e r r - i n g heat i n t o and ou t o f t h e s torage m a t e r i a l and containment o f these PCM systems have y e t t o be addressed.

Thermophysical P roper t y Determinat ion

As i n d i c a t e d i n t h e p rev ious section, t he thermophysical p r o p e r t i e s o f i n t e r e s t t o t h i s program i n c l u d e heat o f fusion, thermal conduct- i v i t y and dens i t y . To date, l i t e r a t u r e searches and o t h e r sources such as, u n i v e r s i t i e s and government l abs have i n d i c a t e d t h a t t h e thermophysical p r o p e r t i e s a re w e l l de f i ned f o r pure s a l t s b u t n o t f o r e u t e c t i c s a l t s o r m e t a l l i c a l l o y s .

NASA Lewis has t h e c a p a b i l i t y t o determine t h e heat o f f us ion . Table 1 shows t h e est imated heat o f f u s i o n f o r severa l f l u o r i d e s a l t m ix tu res i n t h e 1025 t o 1400 K temperature range. heat o f f u s i o n f o r many o f t h e f l u o r i d e s a l t s has now been exper imen ta l l y v e r i f i e d by d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC). Table 2 shows t h e hea t o f f u s i o n o f severa l m e t a l l i c a l l o y s a l s o w i t h m e l t i n g p o i n t s between 1025 and 1400 K. Many heat o f f u s i o n values f o r these m e t a l l i c a l l o y s have been taken f rom B a r i n and Knack.3

Other thermophysical p r o p e r t i e s which must be considered t o determine t h e PCMs e f f e c t on t h e ASD system a re thermal d i f f u s i v i t y and s p e c i f i c heat. developed t o determine d e n s i t y and thermal con- d u c t i v i t y , and t h e c a p a b i l i t i e s o f severa l labora- t o r i e s throughout t h e Uni ted S ta tes are being i n v e s t i g a t e d as p o s s i b l e sources f o r determin ing t h e s p e c i f i c heat and o r t h e thermal d i f f u s i v i t y o f t h e se lec ted PCMs.

The

C u r r e n t l y an in-house c a p a b i l i t y i s be ing

Technical Is=

The systems code has i d e n t i f i e d two types o f phase change thermal energy s torage systems w i t h t h e p o t e n t i a l o f meeting t h e l i g h t w e i g h t and h i g h performance requirements imposed by t h e ASD power system. However, t h e low thermal c o n d u c t i v i t y o f t h e s a l t systems and t h e containment and compat- i b i l i t y issues associated w i t h bo th must be addressed.

Thermal C o n d u c t i v i t y Enhancement

As p r e v i o u s l y s t a t e d one inhe ren t character- i s t i c o f t h e s a l t PCMs i s low thermal c o n d u c t i v i t y which i s c u r r e n t l y be ing enhanced by f i n s and r e f l e c t o r s and r e s u l t s i n a l a r g e and massive ASD power system. enhance t h e thermal c o n d u c t i v i t y i s p r e s e n t l y be ing i n v e s t i g a t e d a t NASA Lewis. i f t h e thermal energy s torage c a n i s t e r s o f t h e h e a t r e c e i v e r shown i n F ig . 10 a re f i l l e d w i t h a m a t r i x o f h i g h thermal c o n d u c t i v i t y f i b e r s , such as g raph i te , t hen s i g n i f i c a n t increases i n thermal c o n d u c t i v i t y a r e poss ib le . f i b e r s w i t h respec t t o t h e thermal energy s to rage

One approach t h a t can be used t o

I n t h i s method,

The l o c a t i o n of t h e

salt is critical to both the thermal conductivity enhancement as well as the location of the voids that form on freezing. If the fibers are wetted by the phase change liquid in specific locations then enhanced thermal conductivity can be main- tained. little as 4% (by vo1ume)of chopped P-100 graphite fibers or vapor grown fibers, the thermal conductivity of LiF should increase by a factor of 2 to 6.

For example, with the addition of as

Containment and Compatibility

that mild steel, pure nickel and Nb-1Zr have relatively good corrosion resistance in molten fluoride salts.4 Unfortunately, only Nb-1Zr possesses some measure of creep strength at ele- vated temperatures. However, it is a refractory metal alloy which requires special handling and fabrication techniques for successful employment. There is therefore much reluctance to use this type of material. Ideally the strength of the containment vessel should be sufficient to with- stand the stresses developed during melting of the solid PCM. Many of the fluoride salts have very large expansions and volume changes upon melting for example, LiF increases in volume about 30 percent when melted. Such behavior could prove disastrous if trapped solid is melted, because the mechanical forces resulting from the volume change could breech the containment vessel wall. Through- out its life the heat receiver's TES unit will be subject to tens of thousands of freeze-thaw cycles under microgravity conditions which pose ill - defined solidification and remelting conditions. It is desirable for the containment vessel to possess adequate strength to cause the solid salt to fracture as opposed to itself. For this to be the case designers must have knowledge o f the strength of the PCMs more specifically the salts because of the large volume changes they experi- ence upon melting.

pure Fe, Nb and Ni to resist attack, it is possible that an alloy containing only these three elements would also be resistant to the molten salts. This offers the potential for developing alloys with inherent high temperature strength, for they can be built on the Ni-Ni3Nb system (with various amounts of Fe) that exhibits behavior similar to Ni-Ni$l which forms the basis for nickel superalloys.

Although, metallic alloys based on Si and Ge possess excellent thermophysical properties, they react with all metals at high temperature and rule out metallic alloys as suitable container materials. Ceramic materials such as Sic and Si3N4 are possible candidates for containment materials, and as indicated by Ref. 5 research is currently being conducted to produce a Si containment shell on a Si-base eutectic alloy sphere. It is evident to all working in the area of containment for Si and Ge-based alloys that much developmental work needs to be done to find suitable container materials.

Prior to the final selection of a PCM for the ASD power system, long term (5000 to 10 000 hr) compatibility testing with potential containment materials must be conducted. Thus, the selection of a phase change thermal energy 4torage material for ASD power systems is based on analytical and metallurgical screening.

Initial compatibility screening has concluded

Based on the apparent ability of essentially

Concluding Remarks

PCM thermophysical properties affect the mass and size of an ASD power system. that high temperature, high heat of fusion and high density phase change thermal energy storage materials must be utilized in order produce small and lightweight ASD systems. To date salt and metal phase change systems have been investigated. As a result of the higher thermal conductivity and density of the metallic phase change systems, as compared with the salt systems, smaller ASD systems were produced.

A literature survey to determine the thermophysical properties of the desired PCMs has indicated that such information is not readily available, or that it does not exist. Therefore, capabilities are being developed in-house to determine the density and thermal conductivity of the PCMs and other sources are currently being investigated as possible sources for determining the specific heat and or thermal diffusivity.

There are several technical issues associated with the PCMs identified as possibly being able to meet the lightweight and minimum mass requirements of NASA Lewis' ASD program. For the salt PCM the major issue is low thermal conductivity and to this end an in-house program is under way to investi- gate the possibilities of enhancing the thermal conductivity with graphite fibers. Another area of concern for both the salt and the metal systems is containment and in the near future a containment development program will be undertaken. For the salt systems a series of Ni-Ni3Nb alloys containing varying amounts of iron will be investigated and for the Si and Ge-based metallic systems ceramic and other new technologies will be explored.

A study has been initiated to determine how

This study has shown

References

1.

2.

3.

4.

5.

6.

Juhasz, A., Coles, C., and Lacy, D., "Analysis of Thermophysical Properties for Advanced Solar Dynamics," AIAA Paper 87-9442, Aug. 1987.

Brandhorst, H.W. Jr., Juhasz, A.J., and Jones, B.I., "Alternative Power Generation Concepts for Space," NASA TM-88876, 1986.

Barin, I . and Knacke, O., Thermochemical Properties of Inorganic Substances, Springer-Verlag, New York, 1973.

Misra, A.K. and Whittenberger, J.D., "Estimated Heats of Fusion of Fluoride Salt Mixtures Suitable for Thermal Energy Storage Applications," NASA TM-87320, 1986.

Misra, A.K. and Whittenberger, J.D., "Identi- fication of Salt-Alloy Combinations for Thermal Energy Applications in Advanced Solar Dynamic Power Systems," NASA TM-88889, 1986.

Misra, A.K., "Fluoride Salts at Phase Change Materials for Thermal Energy Storage in the Temperature Range 1000 - 1400 K," Journal of the Electrochemical Society, 1987, submitted for publication.

3

TABLE 1. - PHASE CHANGE TES CANDIDATES (FLUORIDE SALTS) 1025 TO 1400 K

b930

S a l t mol e%

1

I------ I LiF-22CaF2

KF-15MgF

L i3A1F6

N aF-32CaF2

NaF-23MgF2

L i F

N aF-14A 1 F3

N aF-27CaF2-36MgF2

CaF-50MgF2

N aMgF3-30KMgF3

NaF

NaF-60MgF2

I KF-68.7MgF

Na3A1F6

NaMgF3

MgF3

MgF2

KCaF3 FeF2

Me1 t i n g temperature,

K

7. Bukhalova, G.A., Berezhnaya, V.T., and 8. Beardmore, P., Howlett, B.W., L ichter, B.D.,

of Compounds o f Magnesium and Group I V B Elements," Transactions o f the Meta l lu rg ica l Society o f AIME, Vol. 236, No. 1, Jan. 1966,

Okol'chishena, N.E., l l p y y Propert i res o f and Bever, M.B., "Thermodynamic Propert ies Compounds o f the Type M M Journal o f Inorganic Chemistry, n, No. 7, Ju ly 1969, pp. 917-921.

F3," Russian

PP- 102-108-

1039

1043

1059

1083

1103

1121

1161

1178

1253

1259

1268

1281

1273

1283

1303

1343

1343

1373

1536

~

Heat o f f u s i o n ,

k J / k g

a790

b500

540

5 90

620 b108 7

539

520

610

641

b790

670

a69 0

b53 0

'710

d710

'500

b550

t from aHeat o f f u s i o n d a t a f o r MgF2 o b t a i n e in-house exper imenta l measurements.

bOta ined f r o m B a r i n and Knacke's t e x t .3

CHeat o f f u s i o n d a t a ob ta ined by Bukhalova e t a1 .7

dObtained f r o m ' n house exper imenta l measurements. d -

TABLE 2. - PHASE CHANGE TES

CANDIDATES (METALLIC ALLOYS)

1025 TO 1400 K

Composition, mole Z

Ge

Mg-54.5s i GaAs

ZnP2

Z nAs2

Ca-69Si

I nP

Mg2Si

Mg2Ge

M e l t i n g temperature,

K

1213

1223

1238

1253

1296

1328

1373

1388

aObtained f rom Ref. 3. bOak Ridge Nat iona l Lab data.

Heat o f f u s i o n ,

kJ /kg

51 0 a750

600 730

4 50 b l l 1 0

4 30

1118

705

‘.-STRUCTURE

RADIATOR cur i uc I 1

‘-POWER CONDITIONING LIlU 1 IlC -

FIGURE 1. - COMPONENT BREAKDOWN OF AN ADVANCED SOLAR DYNAHIC POWER SYSTEM.

5

PCWWORKING FLUID TUBE- r GRAPHITE APER-

TURE SHIELD

STRUCTURE

PHASE CHANGE MATERIAL

/ ___---- 7 CONTAINMENT t I CANISTER

I I

CERAN I C BRAZE OR SHRINK-FIT BE- I WORK I NG

FIGURE 2 . - BASELINE SOLAR DYNAMIC HEAT RECEIVER, SHOWING DETAIL OF PCWWORKING FLUID TUBE.

0 LIF NAF

0

LIF-CAF~ 0

. 60 0 LIF cn

3 ' O F

NAF 0

INLET TEMPERATURE, K FIGURE 4. - SPECIFIC MASS AS A FUNCTION OF TEMPERATURE FOR

A 35-KWE STIRLING SOLAR DYNAMIC POWER SYSTEM USING VAR- IOUS PCMs .

LIF MG-SI I

--

(A) RECEIVER SIZ ING BASED ON LIF (SALT) AND MG-SI (METAL).

REFLECTORS7

-FINS

I

iSALT PCM I- GAS FLOW TUBES J' METAL PCM

SALT (LOW CONDUCTIVITY)

METAL (HIGH CONDUCTIVITY)

(B) EFFECTS OF LOW AND HIGH THERMAL CONDUCTIVITY.

FIGURE 5. - COMPARISON OF SALT AND METAL PHASE CHANGE THERMAL ENERGY STORAGE SYSTEMS,

7

HEAT OF FUSION, KJ/KG

3400 0 400 0 600 0 800 A 1044

3000

W Y

v)

3 2600 5 I- v) > v)

2200

1800 900 1000 1100 1200 1300 1400

INLET TEMPERATURE, K

FIGURE 6. - SYSTEM MASS AS A FUNCTION OF INLET TEMPERATURE FOR A 35-KWE STIRLING SOLAR DYNAMIC POWER SYSTEM USING A SALT PCM AT VARIOUS HEATS OF FUSION. NUMBER OF TUBES, 60: NUMBER OF FINS. 6: DENSITY, 1874 KG/M3.

8

240(

220c

c3 Y

v)

3 20oc z I- fn > fn

1800

1600

DENS I TY, - KG/M3

0 1874 0 3600 0 5400

I I I I

9

0 400 1874 0 400 5400 A 1044 400 v 1044 1874

L

t: n L 0 r 7 Q

Q 2000(

n

900 1000 1100 1200 1300 1400 TEMPERATURE, K

1000

FIGURE 8. - SYSTEM MASS AS A FUNCTION OF INLET TEMPERATURE FOR A 35-KWE STIRLING SOLAR DYNAMIC POWER SYSTEM USING PCMs WITH VARIOUS HEATS OF FUSION AND DENSITIES.

10

CONCENTRATOR SLOPE ERROR

STIRLING SD-1 MRAD BRAYTON SD-1 MRAD

20 c

r LIF SOLAR DYNAMIC Cy’ REFERENCE POINT

r SPACE STAT1 ON h

J

FIGURE 10. - BASELINE SOLAR DYNAMIC HEAT RECEIVER SHOWING THERMAL ENERGY STORAGE CONTAINMENT CAN I STER FILLED WITH THERMAL- CONDUCTIVITY-ENHANCING GRAPHITE FIBERS.

11

1. Report No.

NASA TM-89886

Se lec t i on o f High Temperature Thermal Energy Storage M a t e r i a l s f o r Advanced Solar Dynamic Space Power Systems

2. Government Accession No. 3. Recipient's Catalog No.

506-41 -31

4. Title and Subtitle 5. Report Date

Dovie E. Lacy, Carolyn Coles-Hamilton, and A l b e r t Juhasz

7. Author(s)

I E-3569

8. Performing Organlzation Report NO.

10. Work Unit No.

9. Performing Organization Name and Address

Nat iona l Aeronautics and Space Admin i s t ra t i on Lewls Research Center

12. Sponsoring Agency Name and Address

Cleveland, Ohio 44135

11. Contract or Grant No.

13. Type of Report and Period Covered

Technical Memorandum

Nat iona l Aeronautics and Space Admin i s t ra t i on Washington, D.C. 20546

19. Security Classif. (of this report)

Unc lass i f i ed

14. Sponsoring Agency Code 1

20. Security Classif. (of this page) 21. NO. of pages 22. Price'

U n c l a s s i f i e d 12 A02

I 15. Supplementary Notes

Prepared f o r t h e 22nd I n t e r s o c i e t y Energy Conversion Engineer ing Conference, cosponsored by the A I A A , ANS, ASME, SAE, IEEE, ACS, and AIChE, Ph i lade lph ia , Pennsylvania, August 10-14, 1987.

16. Abstract

Under t h e d i r e c t i o n o f NASA's O f f i c e o f Aeronaut ics and Space Technology (OAST), t h e NASA Lewis Research Center has i n i t i a t e d an in-house thermal energy s torage program t o i d e n t i f y combinations o f phase change thermal energy storage media f o r use w i t h a Brayton and S t i r l i n g Advanced So lar Dynamic (ASD) space power systems opera t ing between 1070 and 1400 K. A study has been i n i t i a t e d t o determine s u i t - ab le combinations o f thermal energy s torage (TES) phase change mate r ia l s (PCM) t h a t r e s u l t i n t h e smal les t and l i g h t e s t weight ASD power system poss ib le . To da te the heats o f f us ion o f severa l f l u o r i d e s a l t m ix tu res w i t h m e l t i n g p o i n t s g rea te r than 1025 K have been v e r i f i e d exper imenta l l y . The study has i n d i c a t e d t h a t these s a l t systems produce l a r g e ASD systems because o f t h e i r i nhe ren t low thermal conduc t i v i t y and low dens i ty . I t i s d e s i r a b l e t o have PCMs w i t h h igh d e n s i t i e s and h igh thermal c o n d u c t i v i t i e s . Therefore, a l t e r n a t e phase change m a t e r i a l s based on m e t a l l i c a l l o y systems a re a l s o being considered as p o s s i b l e (TES) candidates f o r f u t u r e AS0 space power systems.

17. Key Words (Suggested by Author@))

So la r dynamics; Thermal energy storage; Phase change mater ia l ; Containment

18. Distribution Statement

U n c l a s s i f i e d - u n l i m i t e d STAR Category 34

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Selection of High Temperature Thermal Energy Storage Materials for