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NASA Contractor Report 191065 /._; -,

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Heat Pipe Heat Transport System for the

Stirling Space Power Converter (SSPC)

Donald L. Alger

Sverdrup Technology

Lewis Research Center GroupBrook Park, Ohio

January 1993

Prepared for

Lewis Research Center

Under Contract NAS3-25266

National Aeronautics andSpace Administration

(,_ASA-C,_-19106,5) HEAT PIPE HEAT

TRANSPJ_,I SYSTEM FOR THE STIRLINGSP_CF P_?WER Cq',_Vi_RTER (SSPC)

(Sv:,rjrup Technolo,#y) II p

N93-22652

unclas

63/20 0150324

https://ntrs.nasa.gov/search.jsp?R=19930013473 2018-07-03T11:28:23+00:00Z

Heat Pipe Heat Transport Systemfor the Stirting Space Power Converter (SSPC)

Donald L. Alger

Sverdrup Technology, Inc.2001 Aerospace ParkwayBrook Park, Ohio 44142

ABSTRACT

Life issues relating to a sodium heat pipeheat transport system are described. The heatpipe system provides heat, at a temperature of1050 K, to a 50 kWe Stirlingengine/linear alterna-tor power converter called the Stiding SpacePower Converter (SSPC). The converter is beingdeveloped under a National Aeronautics andSpace Administration program. Since corrosionof heat pipe materials in contact with sodium canimpact the life of the heat pipe, a literature reviewof sodium corrosion processes was performed.It was found that Impurity reactions, primarilyoxygen, and dissolution of alloy elements werethe two corrosion process likely to be operative inthe heat pipe. Approaches that are being takento minimize these corrosion processes are dis-cussed.

INTRODUCTION

A program is currently underway by theNational Aeronautics and Space Administration todevelop technology for the fabrication of the 50kWe SSPC (1). The development of this convert-er is being performed under contract by Mechani-cal Technology Inc. (MTI). The SSPC will bedesigned with two opposed free-piston StldingEngines, as shown in Figure 1, but only a 25 kWeconverter, one-half of the 50 kWe SSPC, will bebuilt and tested. A smaller version of the SSPC,the 12.5 kWe/piston Component Test PowerConverter (CTPC), has been fabricated to developtechnology for the SSPC (2). The heater head ofboth free-piston Stiding engines will operate at1050 K. The CTPC has been fabricated from

inconel 718 and has a relatively short design life;this power converter will prove all concepts to beincorporated in the final space version SSPC.The SSPC heater head will be made from Udimet720 and has a design life of 60,000 hours. Bothengines have sodium heat pipe heat transportsystems.

This paper will focus upon life issuesrelating to the sodium heat pipe heat transportsystem for the SSPC. Each heat pipe of theSSPC will operate at 1050 K and will transportapproximately 100 kW of heat Into theengine's heater head. Udimet 720 alloy has beententatively selected as the material for the SSPCheat pipe structure, but the material for the wickhas not yet been chosen. Stainless steel (3161_)material has been selected for the CTPC heatplpe wick. Approaches to minimize potentialcorrosion problems associated with these materi-als will be discussed. Dissolution and impurityreactions are the two corrosion processes thatare likely to be operative In a sodium heat pipe.

OXYGEN ENHANCED CORROSION

There was initial concern about theimpurity reactions of elements of the Udimet 720alloy with sodium. Although the word "impurities"can include oxygen, carbon, nitrogen and metallictrace elements such as silicon; oxygen wasconsidered the major Impurity of concern. Earlyin the SSPC program, liquid metal experts recom-mended that the oxygen level in the heat pipe bekept as low as possible (3 and 4). Following thisadvice, a literature search was carded out in aneffort to better understand the problem. Thesearch revealed overwhelming evidence that

oxygenisa majorcauseofcorrosioninbothheatpipeandflowingsodiumloopsystems.Howaparticularmetalwillbehaveina sodium-oxygenenvironmentwill dependon thethermodynamicstabilityof the metal'soxide,at the particulartemperatureof interest,relativetosodiumoxide.

Mostofthesodiumcorrosionliteratureisrelatedtothe interactionofmetalalloysofnuclearreactorsystemswithsodium.Muchofthisworkwascardedoutduringthe1960'sand1970's.Agoodreviewof thisworkisconsolidatedinsever-al handbookseditedbyFoust(5).Johnson,et al(6), pointed out that the presence of the oxygenimpurity can be the controlling factor in manycorrosion and mass-transfer processes. Con-sidering only the impurity oxygen, how soluble isoxygen in sodium and how does it react withcertain alloys to cause corrosion?

Eichetberger reviewed the literature foroxygen solubility in sodium and provided a rec-ommended curve and equation relating thesolubility of oxygen in sodium as a function ofsodium temperature (7). Extrapolating from thiscurve, the solubility of oxygen in sodium at1050 K is estimated to be 8100 ppm. In com-parison, the solubility of metals insodium is a fewppm. For example, at 1050 K, the solubility ofnickel is approximately 4 ppm, chromium 6 ppmand iron 11 ppm (8). At this temperature, thesolubility of molybdenum (9) and niobium (10) insodium is less than 0.3 ppm.

The corrosion of Fe, Cr, Mb, Co and Nbby liquid sodium is a function of the oxygenconcentration (6,11,12). Based on the free-energydata for oxides, the oxides of Fe, Ni, Mb,.and Coare less stable than sodium oxide and will bereduced in sodium to form sodium oxide. Titani-um and aluminum oxides are more stable thansodium oxide and will not be reduced by sodium(13,14).

One mechanism for the corrosion ofmetals in sodium by oxygen Is by the formation ofternary oxides formed from sodium, oxygen anda metal. Although the solubility of metals isnormally very low in sodium in comparison tooxygen, formation of a ternary oxide with sodiumand oxygen effectively increases the solubility ofthe metal in sodium. Horsley first formed andidentified the stable double oxide FeO.(Na20)2(15). According to Gross and Wilson, about 1000

ppm of oxygen is needed to form FeO.(Na20)2(16). Barker and Wood identified several ternaryoxides on the surface of metals exposed to staticsodium which contained dissolved oxygen (17).Ternary oxide compounds that were IdentifiedIncluded: Na=NbO4, Na4TIO4, NaCrO2, andNa4FeO3. Of the oxides identified, only NaCrO2was observed as a strongly adherent compound.Their corrosion experiment showed that at lowoxygen levels, of the order of 50 ppm, onlysodium chromite, NaCrO 2, was found. At veryhigh oxygen levels (0.73 to 4.28 wt.%) thechromite was present with the ternary oxide,Na4FeO3. Both chromium and iron ternary oxideshave been found on surfaces of stainless steel inhigh-temperature, flowing sodium loops. (18,19).A molybdenum ternary oxide, Na3M0206, wasformed in sodium at temperatures above 573 K(18).

Of the elements discussed thus far, nickelseems to stand alone as an element whosecorrosion process is independent of oxygen.Gross and Wilson stated that a ternary oxideinvolving nickel, i.e., the double oxide NiO.(Na20 ),cannot be stable in liquid sodium (16). Borgstedtand Frees found that corrosion rates of nickelspecimens were unaffected by oxygen in theconcentration range between 0.2 to 5 ppm (20).DeVan obtained data Indicating that the masstransfer rate of Inconel X (85% nickel) in flowingliquid metal loops at 1089 K was not measurablyaffected by changes in the oxygen content ofeither sodium or NaK below 500 ppm (21). It isapparent that nickel corrosion occurs only bysimple dissolution of the metal into the sodium.

OXYGEN CAUSED FAILURE OF HEAT PIPES

Jacobson and Lou, following the postmor-tem examination of a failed heat pipe, concludedthat the failure of the heat pipe resulted from theelevated contamination level of liquid sodium, inparticular oxygen (22). In the post-failure analysisof another heat pipe, Jacobson and Wang con-cluded that the failure was caused by the combi-nation of sodium-oxygen corrosion, liquid metalembrittlement and thermal stress corrosion (23).Lundberg and Feber, following postmortemanalyses of molybdenum/sodium heat pipes,concluded that alkali heat pipes indicated impuritycorrosion intheir evaporators. The Impurities thatwere observed to be transported included oxy-gen, carbon, and silicon (24).

LOW-OXYGEN HEAT PIPE DESIGN APPROACH

As discussed, several heat pipe failureshave been caused by the reaction of oxygen withmetal atoms which produced corrosive productsthat eventually perforated the heat pipe wall. Theobvious solution to this problem is to minimizethe amount of oxygen in the heat pipe. Onesuggested method of obtaining a low level ofoxygen in a heat pipe Is to fill the heat pipe withsodium from a high purity sodium loop (4). Theidea is to fill the heat pipe with high purity sodi-um, let it soak in sodium at a particular tempera-ture for a period of time, then drain the sodium.This cycle is repeated several times. This processreduces unstable surface oxides and carries theresultant oxygen from the system yielding anoxide free surface.

Therefore, early in the program, threesmall cylindrical heat pipes were fabricated for thepurpose of developing a heat pipe sodium fillingprocess that used sodlum from a high puritysodium loop. The detailed procedures for per-forming this process were prepared and carriedout by Energy Technology Engineering Center(ETEC) personnel. They have since demonstratedthat heat pipes can be loaded with sodium whichcontains a stable oxygen level of about 10 ppm.The ETEC sodium loop is capable of achieving anoxygen level of less than 1 ppm with refurbish-ment of the cold and hot traps. Therefore, it maybe possible to achieve the sodium loading of aheat pipe which has an oxygen level lower than10 ppm.

DISSOLUTION

Even if corrosion by oxygen relatedmechanisms can be minimized, there remains theprobability that some metal alloy components ofUdimet 720 can dissolve directly into the sodium.In a heat pipe, the rate of dissolution of nickel andother metal constituents of Udimet 720 (nickel,chromium, etc.) depends upon the solubility ofthe metal in sodium and upon the flow rate ofsodium between the evaporator and the condens-er. For example, at 1050 K, the largest metallicconstituent in Udimet 720, nickel, is soluble insodium to a concentration level of about 4 ppm.The heat pipe will only contain a few grams ofsodium and all of this sodium will be in close

proximity to the large surface area presented bythe wick. If the entire heat pipe is heated uniform-

ly to 1050 K, which means that there isn't anymass flow of sodium between the evaporator andthe condenser, the small mass of sodium in theheat pipe will be saturated with nickel within abouta minute. Once saturated, dissolution of nickelinto the sodium will cease. This process is illus-trated for the CTPC heat pipe, shown In Figure 2,by the following calculation. Although this heatpipe is actually fabricated from Inconel 718 andhas a 316L stainless steel wick, for thepurpose of this calculation, it will be assumed thatboth are made of pure nickel.

Non-operational, Uniformly Heated CTPC StarfishHeat Pipe - The dissolution rate for an element,for example nickel, from the metal surface into thesodium can be represented by the followingequation (8,25).

dN/dt

which

N(t) =

N(t) =

= k (No - N(t)) (1)

integrates to

NO(1 - e'kt), where (2)

atoms of nickel in sodium of theCTPC heat pipe at any time, t, where

t = time, sec, and

NO = atoms of nickel in sodium of theCTPC heat pipe at saturation at1050 K, and

k = RA/N o, where

R = dissolution rate of nickel atoms persecond at 1050 K, and

(3)

A = internal surface area of CTPC heat pipe,cm2.

Based upon a CTPC heat pipe sodiumloading of 610 grams (1.6 x 102s atoms) and asaturation value of 4 ppm for nickel (8) at 1050 K,saturated sodium will contain 2.5 x 1019 atoms of

nickel. That is, NO = 2.5 x 1019 atoms of nickel.

A measured nickel corrosion rate in asodium loop at 873 K (20), as corrected to atemperature of 1050 K from data given in refer-ence (26), was used as the dissolution rate, R.R = 2.85 x 1013 nickel atoms/sec/cm 2. Themeasured sodium loop corrosion from references

3

(20)and(26),amountedto a lossof nickelfromthe surfaceat a rate of about 0.01cm/yr (4mils/yr).

TheInternalsurfaceareaof the CTPCheatpipe is approximately1 x 105cm2. Thisincludesthesurfaceoftheheatpipewalls,the2layersof 100meshscreen,and the 50arterieswhicharemadeof 200meshscreen.Therefore,

k = RA/N0 = (2.85x 1013)(1x 105)/(2.5x 1019)

= 0.114,and

N(t)/N 0 = 1 - e"0"114t (4)

After a few substitutions for t, one soonlearns that the sodium becomes 99.9% saturatedwith nickel in about one minute.

Durinq Heat PIDeODeration - Once a temperaturegradient Is established between the evaporatorand the condenser, fresh sodium vapor willcontinuously flow to the condenser and dilutetheliquid sodium in the condenser. Therefore, thedegree of saturation of the sodium of an operat-ing heat pipe is dependent upon the mass trans-fer rate of the fresh sodium.

During heat pipe operation, sodium iscontinuously vaporized from the evaporator wick,condensed on the condenser surface, and re-turned to the evaporator as a liquid through thewick. The pure sodium vapor that condenses onthe wick will dilute the nickel saturated liquidsodium, causing the heat pipe to be unsaturatedwith nickel during operation. A model will besetup to assess the behavior of the CTPC heatpipe in relation to the rate of nickel dissolutionduring heat pipe operation. Since the rate ofcorrosion of nickel from the condenser surface is

of pdme importance because the condenser wallsare load beadng regions of the CTPC heat pipe,only the condenser portton of the heat pipe willbe modelled.

The rate that nickel atoms dissolve intothe condenser sodium from the nickel surface ofthe condenser can be described by equation (1),except that constants k and No must now reflectthe condenser surface area and the amount ofsodium that is contained in the condenser.That is,

dN(t)/dt = kc (No¢- N(t))

where ko = RAt/Not, and

Ac = internal surface area of the CTPCheat pipe condenser, cm2, and

(s)

(6)

Noc = atoms of nickel in sodium of the CTPCheat pipe condenser at saturation at1050 K.

To estimate the rate that nickel atomsleave the condenser per unit of time, It is as-sumed that complete mixing of the nickel andsodium of the condenser will occur. It is further

assumed that the sodium vapor from the evapora-tor condenses uniformly over the condensersurface. The following equation can then bewritten that describes the rate that nickel atomsleave the condenser.

d(Nout(t))/dt = (No(t)/(No(t) + S)) (dS/dt) (7)

= (CPNc(t)/(Nc(t) + S)), where

S = the number of sodium atoms in thecondenser, and

dS/dt = the rate that sodium atoms arriveat the condenser and is also therate that sodium atoms are evaporated from the evaporator.

dS/dt = CP, the rate that sodium is evaporated from the evaporator, where

P = the thermal power Input to theevaporator, Joules/sec, and

C = 6.8 x 10is sodium atoms/Joule,which is calculated from the latentheat of vaporization, 3.85 x 103Joules/gram, for sodium at 1050 K.

A time-stepplng code was written toperform the integration of these rate equations tocompute No(t) according to the following equa-tion.

4

t,,,n

(Nc(t)) i =t=l

[(kc(Noc - (Nc(t))i)dt -

(CP(Nc(t))i/((Nc(t)) i+ S)dti=m

] (8)i=1

For the first time increment, kc was set equal toN¢(t) and a first value of Ne(t=l)i=l was calculat-ed for the first iteration, i = 1. This value wassubstituted into equation 8 and a new value ofNc(t = 1)i=2 was calculated. This iteration processwas continued until a constant value of

No(t=l)i=m was calculated after m iterations.No(t= 1)i=m was then substituted into equation 8to compute the first value of Nc(t=2)i= 1 for thesecond time increment. The process is thencontinued until t = n.

Result_ - At a heat pipe heat transfer rate of 50kW, a steady state level of nickel in the condenseris reached in approximately 30 seconds at anNc(t)/N0c ratio of 0.638. At this steady statelevel, where nickel is being dissolved into thecondenser at the same rate that nickel leaves the

condenser, nickel passes through the condenserat a rate of 3.4 x 1017 atoms/sec. Based uponthe CTPC heat pipe condenser surface area of3.298 x 104 cm2, this corresponds to a loss ofnickel from the surface at a rate of 3.6 x 10 .3

cm/yr (1.4 mils/yr). This is about one-third of thesodium loop corrosion rate, 0.01 cm/yr (4mils/yr) presented in references (20) and (26) thatwas used to estimate the dissolution rate con-stant, R, given in equations (3 an (6). The calcu-lation was repeated for power levels of 5 kW and500 watts. As shown in Table I, the rate of nickelloss is nearly directly proportional to the power.

TABLE I

Estimated nickel corrosion rate for condenser foran all-nickel CTPC type heat pipe

Power N/N 0 Nickel Corrosion RatekW Atoms/sec cm/yr (mils/yr)

0.5 0.9944 5.30 x 1015 5.6 x 10.5 (0.02)

5.0 0.9463 5.05 x 1016 5.3 x 10-4 (0.21)

50 0.6379 3.40 X 1017 3.6 x 10-3 (1.4)

DISCUSSION OF DISSOLUTION RESULTS

In comparison to the corrosion rate forthe sodium loop, 0.01 cm/yr (4 mils/yr), thecomputed heat pipe corrosion rates are muchsmaller. This is because the sodium in the con-denser becomes partly saturated with nickel asshown by the N/N 0 ratio in Table I. At the 50 kWdesign input power level for the CTPC heat pipeevaporator, a nickel corrosion rate of 3.6 x 10-3cm/year (1.4 mils/yr) is higher that desired for thelong-life SSPC heat pipe, but still Is acceptablewith appropriate design modifications of the SSPCheat pipe. However, there is considerable heatpipe experimental data, discussed below, whichsuggests that the actual rate may be much lower.Furthermore, the analysis that has just beenpresented was done for pure nickel, not nickelalloy, and is based upon a number of assump-tions. For example, there is experimental evi-dence which shows that dissolved nickel is notuniform over the thickness of the wick structureas assumed for this analysis, but that a nickelconcentration gradient occurs over the wickthickness. Therefore, the analysis is meant todefine a maximum probable nickel corrosion rateand to point out the need to measure actualcorrosion rates in operating experimental heatpipes. This is the approach that has beenplanned, is underway, and will be discussed in thefollowing paragraphs.

Pure nickel heat pipes have been operat-ed for extensive periods of time without anyindication of a mass transfer of nickel. DeVanand Jansen (27) performed a metallurgical exami-nation of three pure nickel heat pipes, whichincluded nickel wicks. The heat pipes had beenoperated at 873 K at a nominal power level of

1750wattsoveratimeperiodrangingfrom 6,000to 10,000 hours. They concluded that masstransfer from the condenser did not occur to anysignificant extent. Although the working fluid Inthese heat pipes was potassium, it was stated inthe report that potassium and sodium are verysimilar with regard to dissolution behavior.Harbaugh (28) reported the testing and metallurgi-cal examination of another pure nickel heat pipe,also operated at 873 K at a nominal power levelof 1750 watts, but for a time period of 21,000hours. This heat pipe also contained potassiumas the working fluid. No mass transfer of nickeloccurred from the condenser of this heat pipe.

Other experimental evidence Indicate thatactual corrosion mechanisms that occur in heatpipes may be more complex than is described byequation (1). For example, Jacobson and Lou(22), during their post-test examination of aninconel 600 heat pipe with a pure nickel wick,concluded that although there was a change inmaterial composition of the heat pipe wall surface,the condenser region had not exhibited anynoticeable corrosion during neady 5000 hours oftesting at 1144 K. The iron content decreasedfrom 8% to 3.5%, the chromium content decreas-ed from 15.5% to 4%, and the nickel contentincreased from 76% to 91%. That is, nickel hadtransferred radially from the pure nickel wick tothe nominally 76% nickel Inconel 600 wall. Walak(29) experienced a similar phenomenon. As apart of the current SSPC development program,he operated an Inconel 718 heat pipe which wasconfigured as a creep test specimen and testedfor 1090 hours. The working fluidwas sodium andthe wick material was pure nickel. The heat pipewas operated over a temperature range between1000 K and 1050 K. During post-test metallurgicalexamination of the Inconel 718 heat pipe con-denser wall surface, Walak found that the ironcontent decreased from 19.03% to 13.76%, thechromium content decreased from 18.45% to11.61%, and the nickel content increased from52.1% to 69.19%. That Is, nickel had also trans-ferred radially from the pure nickel wick to theInconel 718 condenser surface.

These experimental results point out theneed, during modelling of the dissolution of heatpipe materials, to include the affect of differencesin composition between wick and wall materials.As will be discussed later, it may be advanta-geous to intentionally have a higher content of

nickel in the wick in order to protect the heat pipewall.

APPROACHES TAKEN TO ADDRESS POTENTIALDISSOLUTION PROBLEMS

As discussed, three small, cylindricalInconel 718 heat pipes were fabricated and usedto define the sodium filling process. The wickmaterial for these pipes was made from 316Lstainless steel. One of these heat pipes was filledby a process which used commercial gradesodium. The other two pipes were tilted withsodium by a newly defined process which usedsodium from a low-oxygen sodium loop at ETEC.A similar Inconel 718 heat pipe has also beenfabricated that contains a pure nickel wick. All ofthese heat pipes are being prepared for long-termtesting. A pie-shaped heat pipe, one-tenth thesize of the CTPC heat pipe, has been fabricatedfrom Inconel 718 by MTI and is currently beingcleaned and loaded with sodium by ETEC. Thewicking of this heat pipe Is also 316L stainlesssteel. At the conclusion of these tests, the heatpipes will be opened and metallurgically examinedto look for corrosion and mass transfer. Similar,small, Udimet 720 heat pipes will also be fabricat-ed and subjected to long-term testing followed bymetallurgical analysis. All of the data obtainedfrom the above mentioned heat pipe testing willbe used for the final selection of materials for theSSPC.

The fins that make up the condenserregion of the CTPC heat pipe have a surface area,less wick cover, that is less than 5% of the totalIntemal surface area of the heat pipe. Althoughthe fins constitute a small percentage of thecondenser area, the fin surface Is very criticalbecause the fin is a load beadng member of theStirllng engine and must be fabdcated fromstrong, high-temperature materials like Inconel718 or Udimet 720. As shown in Figure 2, eachfin contains gas passages which contain the highpressure helium working fluid at a nominal pres-sure of 15.0 MPa. During operation, the gas pres-sure fluctuates between about 13.5 to 16.5 MPa.The nominal wall thickness between this gas andthe condenser wall Is 0.75 mm. Because of thevarying gas pressure, this wall is subject tofatigue failure. In addition, each fin is subjected toan axial tensile stress. As soon as it is under-stood how dissolution affects the superalloy heatpipes that are being tested, this information will

6

be used to determine methods to protect the finwall from corrosion.

The data presented by Walak (29) pres-ents an interesting possibility. If the wick is purenickel, nickel will deposit on the nickel-base alloy(Inconel 718 or Udimet 720) condenser wall andprotect the surface. On the other hand, onewould expect that if the wick is stainless steel,nickel may transfer from the nickel alloy wall tothe stainless steel wick thus depleting nickel fromthe nickel alloy condenser surface, an undesirablesituation. The heat pipe testing previously dis-cussed should help to clarify the best designapproach.

The wick of a CTPC heat pipe constitutesabout 85% of the total interior surface area of theheat pipe. Since the wick is not a load bearingpart of the heater head and does not require highstrength materials like Udimet 720, a wide rangeof materials is available for selection.

Finally, we are investigating the potentialuse of coatings to provide a barrier that may slowthe rate of corrosion of the heat pipe materials.That is, such a coating will directly reduce thedissolution rate constant, R, used in equations (3)and (6). One material that is being considered isnickel aluminide. This matedal has been provento be a very effective corrosion resistant coatingfor sodium loops in nuclear reactor applications(30).

CONCLUSION

A literature search relating to the corro-sion of nickel-base alloys by sodium was con-ducted. The results cleady indicate that thepresence of impurities inthe sodium, in particular,oxygen, can cause corrosion of the nickel-basealloy. Although the corrosion rate of most com-ponent elements of nickel-base alloys is depen-dent on the amount of oxygen contained in thesodium, corrosion of nickel is not oxygen depen-dent. It appears that corrosion of the nickeloccurs by simple dissolution of the nickel into thesodium. The corrosion rate of nickel that hasbeen measured in flowing sodium loop systemsdoes not appear to apply to a heat pipe environ-ment. Based upon the information gleaned fromthe literature search and simple analyses, heatpipe experiments have been planned to directly

measure corrosion rates in heat pipes. Theresults will be applied to the design of the finalStirling Space Power Converter.

REFERENCES

. J. E. Dudenhoefer and J. M. Winter: Status ofNASA's Stirling Space Power ConverterProgram, Proc. of 26th IECEC, August, 1991.

. G. Dochat: Free-Piston Stiding ComponentTest Power Converter, Proc. of 26th IECEC,August, 1991.

3. L Tower, personal communication.

4. J. DeVan, personal communication.

O. J. Foust, ed.: Sodium-NaK EngineeringHandbook, Vol. 1 - 5, Gordon and Breach,Science Publishers, Inc., 1972.

= H. E. Johnson: Chemistry, in Sodium-NaKEngineering Handbook, Vol. 1, Gordon andBreach, Science Publishers, Inc., 1972, p. 238.

7, R. L. Eichelberger: The SolublUty of Oxygen inLiquid Sodium: A Recommended Expresslon,U$AEC Report AI-AEC-12685, Atomic Inter-national, Nov. 1, 1968.

. J. R. Weeks and H. S. Isaacs: Corrosion andDeposition of Steels and Nickel-Base Alloys inLiquid Sodium, in Advances in CorrosionScience and Technology, Vol. 3, Plenum Press,1973.

9. Ibid 6, p. 244.

10. R. L. McKlsson, R L Eichelberger, R. C.Dahleen, J. M. Scarborough and G. R. Argue:Solubility Studies of Ultra Pure Transition Elements in Ultra Pure Alkali Metals, NASA CR-610, Oct., 1966.

11. J. R. Weeks, C. J. Klamut, and D. H.Gurinsky: Corrosion by the Alkali Metals, in

Alkali Metal Coolants, Proc. of a Symposium,Vienna, Nov. 28-Dec, 1966., Int. AtomicEnergy Agency, Vienna, 1967, p. 15.

7

12. A. W. Thodey and C. Tyzack: CorrosionBehavior of Steels and Nickel Alloys in High-Temperature Sodium, inAlkali Metal Coolants,Proc. of a Symposium, Vienna, 28 Nov-2 Dec.,1966, IAEA.

13. C. Tyzack: The Behavior of Materials inLiquid Sodium, In Advances in Materials,InterdisplinarySymposium, Culcreth,England,1964, pp 239-265.

14. W. Clough, Free-Energy Calculations onReactions of Oxides and Iodides in Sodium, J.of Nuclear Energy, 1967, Vol. 21, pp 225-232.

15. G.W. Horsley: Corrosion of iron by Oxygen-Contaminated Sodium, J. of Iron and SteelInstitute, Jan., 1956, pp. 43-48.

16. P. Gross and G. L Wilson: CompositionandHeat of Combination of a Double Oxide ofiron and Sodium, J. Chem. Soc. (A), 1970, pp.1913-1916.

17. M. G. Barker and D. J. Wood: The ChemicalComposition of Corrosion Products in LiquidSodium, in Chemical Aspects of Corrosionand Mass Transfer in Liquid Sodium, ed. by S.A. Jansson, Proc of Symposium, Detroit,Mich., Oct. 19-20, pp. 365-379.

18. C. C. Addison, M. G. Barker, and R. J.Puiham: Reactions of Liquid Sodium withTransition-metal Oxides. Part I. The Dioxidesof Molybdenum, Tungsten, and Uranium, J.Chem. Soc., 1965, pp. 4483-4489.

19. R. H. Hiltz: The Corrosion of Stainless Steelin Oxygen-Contaminated Sodium at 1200 Fand 1400 F, in Corrosion by Liquid Metals, J.E. Draley and J. R. Weeks, Plenum Press,1970, pp. 43-8O.

20. H. U. Borgstedt and G. Frees: RelationsBetween Corrosion Test Results and a Possible Mechanism of Liquid Sodium Corrosion,inChemical Aspects of Corrosion and MassTransfer in Liquid Sodium, ed. by S. A.Jansson, Proc. of the Symp., Detroit, Mich.,Oct. 19-20, 1971, p. 265.

21.

2.

J. H. DeVan: Corrosion of Iron-and Nickel-base Alloys in High Temperature Sodium andNaK, in Alkali Metal Coolants, Proc. of aSymposium, Vienna, Nov. 25-Dec 2, 1967, pp.643-661.

23.

D. J. Jacobson and B. S. Lou: Sodium,Inconel 600 Heat Pipe Life Test Analysis,AIAA/ASME 4th Joint Thermophysics andHeat Transfer Conference, June 2-4, 1986,Boston, Mass.

24.

D. L Jacobson and J. H. Wang: FailureAnalysis of a Sodium, Inconel 617 Heat Pipe,AFWAL-TR-85-2064, Sep., 1985.

25.

L B. Lundberg and R. C. Feber, Jr.:Corrosion in Alkali Metal Molybdenum HeatPipes, AIAA 19th Thermophysics Conference,June 25-28, 1984, Snowmass, Colorado, AIAA-84-1722.

26.

L. F. Epstein: Static and Dynamic Corrosionand Mass Transfer In Liquid Metal Systems,Chem. Engr. Progress Symposium, No. 20,Vol. 53, 1957.28.

27.

B. A. Nevzorov: Corrosion of StructuralMaterials in Sodium, 1968, translated fromRussian by C. Nisenbaum, 1970, TT69-55017,AEC-TR-6984, UC-25.

J. H. DeVan and D. H. Jansen: Examinationof Nickel Heat Pipes Containing Potassium,ORNL-TM-3077, Dec., 1970.

28. W. E. Harbaugh: The Development of a 600oCentigrade Heat Pipe Assembly, Final Technical Report, TL-317-82-994-99, U. S. AtomicEnergy Commission, April 30, 1989.

29.

0.

S. Walak: Heat Pipe Fatigue Test SpecimenMetallurgical Evaluation, NASA ContractorReport number CR 189120, June, 1992.

R. N. Johnson: Tribological Coatings forLiquid Metal and Irradiation Environments, J.Mat. for Energy Systems, Vol. 8, NO. 1, June,1986, pp 27-37.

8

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_'_-HEAT PIPE EVAPORATOR

""" EXPANSION SPAGE

"" BEARING PORTS (TYP.)

HELIUM WORKING FLUID

Rgure 1.--S§ding space power converter.

-1

Figure 2.--Seclton view showing fins and condenser slot regions

of CTPC Starfish heat pipe.

9

Form Approved

REPORT DOCUMENTATION PAGE OMB No. 0704-0188

Pul0_ reportfogburden for this collecllonof informationis estimated to average 1 hour per response, including the time for reviewinginstruCtions,eel=re/Ringexistingdell sources,galhertngand maJnteiolngIhe data needed, and completingand reviewing the cotiectlonof information. Sendcommentsregardingthis burden estimate or any other aspecl of b_iscoliocronof information, including suggestionsfor reducingthis burden, to Washington HeadquartersServices,Directoratefor information Operations and Reports. 1215 JeffersonDavisHighway,Suite 1204, Arlington,VA 22202-4302, and to the Office of Management and Budgel, PapentOrkReductionProleot (0704-0188), Washington,DC 20503.

1. AGENCY USE ONLY (Leave blink) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED

August 1992 Final Contractor Report"4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Heat Pipe Heat Transport System for the Stifling Space Power

Converter (SSPC)

6. AUTHOR(S)

Donald L. Alger

T. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Sverdrup Technology, Inc.

Lewis Research Center Group

2001 Aerospace Parkway

Brook Park, Ohio 44142

9. SPONSORING/MONITORINGAGENCYNAMES(8)ANDADDRESS(ES)

National Aeronautics and Space AdministrationLewis Research Center

Cleveland, Ohio 44135-3191

WU-590-13--11

NAS3-25266

8. PERFORMING ORGANIZATION

REPORT NUMBER

F.,-7118

10. SPONSORING/MONWORINGAGENCY REPORT NUMBER

NASA CR-191065

11. SUPPLEMENTARYNOTES

Project Manager, James E. Dudenhoefer, Power Technology Division, NASA Lewis Research Center, (216) 433--6140.

Prepared for the 27th Intersociety Energy Conversion Engineering Conference sponsored by the SAE, ACS, AIAA,ASME, IEEE, AIChE and ANS, San Diego, California, August 3-7, 1992.

12a. DISTRIBUTION/AVAILABILITYSTATEMENT

Unclassified - Unlimited

Subject Category 20

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Life issues relating to a sodium heat pipe heat transport system are described. The heat pipe system provides heat, at a

temperature of 1050 K, to a 50 kWe Stifling engineflinear alternator power converter called the Stifling Space PowerConverter (SSPC). The converter is being developed under a National Aeronautics and Space Administration program.

Since corrosion of heat pipe materials in contact with sodium can impact the life of the heat pipe, a literature review of

sodium corrosion processes was performed. It was found that impurity reactions, primarily oxygen, and dissolution of

alloy elements were the two corrosion process likely to be operative in the heat pipe. Approaches that are being taken tominimize these corrosion processes are discussed.

14. SUBJECT TERMS

Stifling engines; Heat pipes; Sodium; Liquid metal

17. SECURITY CLASSIFICATIONOF REPORT

Unclassified

NSN 7540-01-280-5500

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

115. NUMBER OFPAGES

1016. PRICECODE

A02_. LIMITATION OF ABSTRACT

Standard Form 298 (Rev. 2-89)

Presc:rlbed by ANSI Sial. Z39-18298-102

National Aeronautics and

Space Administration

Lewis Research Center

Cleveland, Ohio 44135

Offlciml Bustne#ms

P_mnml1_Ffo_' Prlvmte Uee 1300

FOURTH CLASS MAIL

ADDRESS CORRECTION REQUESTED

IIIIII

Poslage anO Fees P;_I,J

Nahonal Aeronaul_.s anclSoace A(Jminlslrah(=n

NASA 451

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