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AD840279

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TOApproved for public release, distributionunlimited

FROMDistribution authorized to U.S. Gov't.agencies and their contractors;Administrative/Operational Use; Sep 1968.Other requests shall be referred to NavalUnderwater Warfare Center, Pasadena, CA.

AUTHORITY

USNURDC ltr, 7 Dec 1971

THIS PAGE IS UNCLASSIFIED

NUWC TP 74

CO

DISTRIBUTION STATEMENT

This documunt Is subject to special export controls and each trmmlttal to foreign governments ormign, nationals may be made only with the prior approval of the Naval Undsmsea Warfare Center,

At0

1CFSfl WRITE lf~P C BUFF SEVT ,

jJIFCA I log

A ,N~y L UNDERSEA WARFARE CENTER

H. Lowe, Capt., USIN Wil. !S. McLean, Ph.D.

Commander Technuo~a Director -

This report presents results of an investigation to determinean underwater power source suitable for long missions at greatdepths. Thermal energy stored in a molten lithiurn salt mixturewas used to generate steam that could be used to power a closed-cycle system. The thermodynamic properties of the salt, aswell as the corrosive action of the salt on container materials,was investigated.

The information included here was presented to the ThirdPropulsion Joint Specialist Conference of the American Institute

of Aeronautics and Astronautics, Washington, D. C., in July 1967. [The work was performed under Bureau of Naval Weapons TaskAssignment ASW 20Z-OOO/216-1/F1O8-Ol-33 during the period1 964 through 1966.

Released by Under authority of

D. VERONDA, Head 3. H. J NNISON, HeadProduct E gineering Division Engineering Department

3. H. GREEN, Head D.A. KUNZ, HeadApplied Sciences Division Oceani Technology3 September 1968 Department

Th. distribution control point for tlis report is NUWC, Paaea, California 91107 i-

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f!

L NESE AFRECNE

in ~ ~ ~ ~ ~ ~ ~ ~ ~~~~~~' aS t

I

PROBLEM

Develop an energy source that can be used togreat ocean depths with minimum deterioration ofperformance or change in system buoyancy.

RESULTS

An analysis of various thermal storage materialsindicated that a eutectic mixture of lithium hydroxideand lithium fluoride would provide relatively highspecific energy for a closed thermal propulsion cycle,and would cause no buoyancy change when containedin a pressure vessel. Tests were conducted to deter-mine the physical properties as well as the corrosivenature of the salt mixture. A study determined thatInconel 600 is the best single material for containingthe molten salt under high pressures.

RECOMMENDATIONS

The salt combinations studied have many desir-able characteristics, especially at temperaturesbelow 10000 F. Above that temperature, severe cor-rosion problems exist. In addition, a reduction inthe strength of Inconel 600 occurs when small amountsof sulphur are present. These two problems should

* be studied carefully before further development of asystem utilizing LiF-LiOH as a thermal storagemedium.

iii

- , - - - - - -

C

CONTENTS

Intro.duction.................................................... 1

Experimental S5team Boiler..................................... 6

Corrosion..................................................... 9

Salt Characteristics ............................................. 11

Change in Melting Point......................................... 12

Water Solubility in (.he Eutectic Mixture.......................... 14

Conclusions.................................................... 15

iv

INTRODUC TION

An ASW system now under investigation at the Naval Undersea War-fare Center (NUWC) requires an unmanned, deep-operating sonarsurveillance vehicle with a very long endurance capability. Obviously,atomic energy is the only present source that could provide the neces-sary power throughout the complete mission. However, no applicablenuclear power source is likely to be available in the foreseeable future. IAs a result, an investigation of relatively short-endurance propulsionsystems and energy sources was undertaken.

The investigation =entered around systems capable of quick re-charge or refueling from a surface vessel at sea. In this context,quick recharge was to imply a period of 6 hours or less.

In addition to quick recharging or refueling, the system should meetfour other criteria:

I. It should be capable of achieving extreme depths without reduc- ition of performa. ;e. i

2. Any change in buoyancy or center of gravity should be minimalto eliminate trim problems.

3. Hazards to the crew of the tending ship must be minimal.

4. The propulsion system should be quiet, so as not to interfere iwith sonar systems.

With these limitations in mind, many possible energy sources wereconsidered, and a eutectic lithium fluoride-lithium hydroxide molten Isalt thermal energy storage system was further studied as a prospec-tive energy source. Some of the available energy sources are reviewedin the following paragraphs to illustrate how the LiF-LiOH eutecticcompares with other energy sources.

Thermal Combustion Engines. The combustion engine has severaldisadvantages in deep operation. It is depth-sensitive if the prod-ucts of combustion are exhausted directly overboard against high

4'

I, 1

backpressures. In fact, additional equipment is required if the productsof combustion are to be pumped overboard or stored. Furthermore,trim becomes a problem if the center of gravity or buoyaacy changesas the fuel is consumed, so that a ballast or buoyancy compensationsystem is required. Trim is particularly critical in the case of slow-moving submerged vehicles.

Batteries. Conventional storage or rechargeable batteries aremore favorable with respect to buoyancy control than the combustionengine. However, the available energy per charge in batteries is quitelow, the number of times that a battery can be recharged is limited,and the battery's high negative buoyancy can impose a considerablepenalty if additional material is required to provide neutral buoyancyfor the system.

Thermal Energy Storage Systems. Several thermal storage systemshave considerably higher specific energy storage capabilities than lead-acid or silver-zinc batteries. and they also provide constant buoyancy.Although thermal storage systems do not match the theoretical per-formance of some thermal combustion or fuel-cell systems, the thermalstorage system investigated by NUWC has the advantage of being re-chargeable by means of superheated steam supplied from a surfaceyes el.

The thermal energy that can be stored in the eutectic comparesquite favorably with other energy sources. Figure I is a nomographof endurance versus specific energy for various energy sources thathave been considered for underwater powerplants in small submergedvehicles, which would range from 200 to 600 cubic feet in size andrequire from 50 to 100 shaft horsepower. The vertical width of theband for each type of energy source is indicative of the penalty paidfor the addition of buoyancy material or containers necessary to pro-vide neutral buoyancy. The bottom line of each band represents thepossible energy and endurance for each system, while the top line in-dicates the net available energy when buoyancy material and containersare included. On this basis, the eutectic thermal storage systemapplied to a Rankine cycle steam engine appears to be very favorablein comparison with rechargeable batteries. The narrowness of thecross-hatched area for the salts is indicative of the relatively smallpenalty incurred with their use when neutral buoyancy is required.

Fuel cells would appear to provide the greatest endurance, basedon specific fuel consumption only. However, space requirements forauxiliary equipment would appear to be too great for smaller vehicles,

2

8070

30 -(5 lcrcmtr

~20 -LiF-LIOH heut storage at 20Y. thermal

10

SSubmerged vehicle size: *%.~%. ciency (containe at-6

5 1. 600-ft3 displacement with 2/3

3 for enrgy source (50 ohp) I2 aIncluding buoyancy material at 39 lb/ft3 seii

1 2 3 4 5 678910 20 30 40506O 00100 200

Endwswne, hr at IS Knotsj

FIG. 1. Submerged Velicle Endurance With Various Enery Sourcs.

and there are many problems in an undersea environment thpt must beovercome before the fuel cell can be seriously considered for smallsubmerged vehicles.

Proposed System. The proposed propulsion system which usesthermal storage as the energy source. is basically a Rankine orclosed-cycle steamn system with boiler tubing embedded in eutecticsalts. A much simplified schematic is shown in Fig. 2. The boilertubing is used both to extract the heat from the salts by generatingstcam. and to recharge the eutectic salts with superheated steam.from the tending vessel. Electrical heaters were not chosen foruse in the charging cycle because they would add consideroble extraweight The boiler tubing was investigated for use as possible re-sistances elements for electric heating. but excessive corrosion

3

occurre. because of the conductivity of the salt and the resultingelectrolytic action.

makm

FUG2.SiplFeed w Datme r a Mle al ht udha

Anoheradantge o a u otenestsyse sta h R a yc

nuclear.2 persiurcfe become Darailable for faltuTbr& smnalubesil

applications.

Several propulsion syvtems using a molten salt for thermal energystorage have been, investigated by other laboratories for underwatervehicles and various missions. In general, thee* systems would pro.vide much greater specific energy per charge than conventional storagebatteries. and would also provide constant buoyancy for deep operation.HOWeve most of these systems used either lithium hydride or lithiumflrideo as the energy into age medium. and each has several undetir-able feaftres. Lithium hydride, which has the highest energy density

of tbo Uithium salt was not considered satisfactory for *tro* reasons-

4

1. It is violently reactive in contact with water, and hence is ahazard to personnel during handling.

2. It has a 16-to-19% shrinkage factor during fusion, which mightcause severe stresses within the heat exchanger when cycled re-peatedly.

3, It has a melting point of 1256 F, which makes recharging withship's steam difficult.

Lithium fluoride was discarded as a sole source of energy becauseof its high melting point (15560F) and high negative volumetric changeduring freezing (25%).

Lithium hydroxide, another lithium salt investigated, has a morefavorable melting point of 884' F and also a low volumetric changeduring freezing. The volume change is unusual, in that lithium hy-droxide expands 3.4% on freezing, which is similar to ice. Althoughthe v Aumetric change of lithium hydroxide is low in comparison withother salts, there was apprehebsion that difficulty might be experiencedin the design of a vessel and heat exchanger to withstand possiblestresses during repeated cycling. To counteract this expansion, vari-ous amounts of lithium fluoride were added to the lithium hydroxide.When 20 to 30%. lithium fluoride by weight was added, practically nochange in volume was noted and the melting point of the mixture was8006 F. This led to the discovery that the point of no volume changecorresponds nearly to the eutectic point of the mixture, and would pro-vide i salt with both a low volumetric change and a low melting point.The phase diagram of these materials in Fig. 3 confirmed this eutecticpoint, but very little information was available on the thermodynamicproperties or chemical reaction of the eutectic with other materials.Therefore. before the undertaking of an extensive test prograr, itwas decided (1) to make some preliminary tests that might revealproblem areas, and (2) to determine the feasibility of using this saltcombination as a thermal storage medium.

5I

. , , i s ' it i ' L . . . i II I - I ilt I I Il

11 i S li ill H i illl llil I -II I lI HB ll il I

1600

800

700i

1200

J6000

300 100 20 40 60 s0 100

LIP MoeuarLOH

FIG. 3. Lithium Fluarlde-Lithium Hydroxide (LIF-LIOH)

Phase Diagram.

EXPERIMENTAL STEAM BOILER

A small heat -storage chamber was constructed to determine thepracticality of generating steam from the hot salt. Also ~o be deter-mined were the approximate thermodynamic properties involved andthe corrosivity or breakdown of the eutectic mixture during repeatedcycling in contact 'With available structural materials, suich as stain-less ateel or Ttcouel. Figure 4 shows a schematic layout of the test

6

SteamI

10-in, diameter 4j

Asbestos clothhetn

I Ilk

304 Stainlerss steel,2.88-in. MD

1i4oJken salt

Johns-ManvileSuperex lnilation

Water

FIG. 4. Experimental Molten Salt Steam Generator; 12-lb Salt Capacity.

setup. The thermal storage container had a 3-inch internal diameterand a length of 36 inches. A heat-exchanger tube was positioned co-axially in the chamber. The tube was 0,5 inch in diameter, and had awall thickness of 0.035 inch. Both the tube and the container were con-structed of Type 304 stainlers steel. The apparatus contained I? poundsof the eutectic mixture. Inconel- sheathed thermocouples were locatedat various elevations in the container and the steam tube. The outersheU was encased in high-temperature insulation (Johns-Manvill eSuperex). An Inconel-sheathed resistance heating element was in-mersed in the salt to melt the mixture.

Afer heating the salts to a molten state, distilled water was intro-duced into the bottom of the steam tube by a Sprague pump at pressuresup to 1,000 psig. As the water flowed up the tube, it was transformedto steam by the heat abserbed from the hot salt. At the beginning ofthe run, the majority of the heat was extracted only from the lowerpart of the apparatus. As the run progressed, the heat was extractedat higher and higher locations until, at the end of the run, the top partof the salt had cooled below 700" F. A typical run record is shown inFig. 5. Note that it is important to be able to extract heat from thesalt in a stratified manner. More heat can thus be obtained from thesalt, and steam can be generated at higher temperatures than would bepossible if the salt cooled uniformly.

1200

1100 Temperature ear top of sa l

1000 Temperature of seam

SO0 - Temnperature In center of salt

400

200 _ Temperature war bottom of salt

100-01

0 10 20 :0 40 s0 60 70 80 90 100

Time, rain

FIG. . Tempoezme-Veazs-Time Cooling Curves for Expermental12-b Stean Go netor With a Water Flow Rate of 4 lb/ih.

a

~I

In one run, superheated steam was generated at temperatures be-tween 700 and 1200"F at 1,000 psig for 1.5 hours at a rate of 4 poundsper hour; in another run, the period was 4 hours at a rate of 1.5 poundsper hour. A total flow of 8 pounds of steam was possible at low flowrates, which indicated that the available heat is approximately 1,000 Btuper pound of the eutectic salt mixture. A third test run was made, inwhich the steam temperature fell from 12000 F to 7000 F in 17 minutes, Iwith a flow rate -f 15 pounds per hour. An additional 4 pounds ofsuperheated steam was generated by lowering the flow rate.

CORROSION

About 30 test runs were made with the 12-pound unit, during whichthe salt mixture was in the molten state at temperatures from 800 to1300 F for approximately 20r hours, and in the partially molten stateduring reheat for several times that long. No deterioration of thesalts or failure of the steam tube, Inconel-sheathed thermocouples, orthe heater exposed to the salts was detected from test data taken duringthis period. The tesits were then discontinued, as it was believed thatsufficient information had beer. obtained for preliminary design pur-poses,

The 12-pound salt container was latav rut into sections. Only thebottom portion of the salt column indicated deterioration, as shown bycorrosion products that had settled there. The upper portions of thecolumn appeared to be uncontaminated. The wall of the stainless-steeltube underwent some corrosion at the upper section, where high tem-peratures were sustained for greater periods of time. However, mostof the corrosion was on the inside surface, which was exposed to steamonly. These results were considered quite favorable, especially sincethe material used for construction was commor 304 stainless steel.

Nevertheless, subsequent tkests on samples of various metals indi-cated that rapid corrosion may occur. It was therefore considerednecessary to conduct a more extensive investigation to determine thebest materials to withstand corrosion, and to determine the conditionsthat cause accelerated corrosion. A contract for this investigation waslet to Atomics International, Division of North American Aviation,Canoga Park, California.1

t DeVtes, G., and L. F. Ga~ham. "Comdon of Metals in ta Molten LIOH-LiF-H20 Syftm,"Ilectocbemical Technology, Jily -August 1967, Vol. 5, No. 7-8, p. 335.

9

___

nnm ____mm 4 l Nu nmdn • mmn

Screening tests were made on nearly 50 different metals and alloysto determine those which were worthy of further study. Nickel, somenickel-based alloys, and the precious metals, silver, gold, and plati-num proved to have the best short-term corrosion resistance. Longer-term tests of 550 hours were conducted on nickel and nickel-basealloys. The two most promising containment materials indicated werenickel and Inconel 600. The average corrosion rates during the 550-hour test were 0.027 mil/day for nickel and 0.27 mil/day for Inconel 600at a test temperature of 1200* F.

The effect of temperature on the corrosion rate is shown in Fig. 6.As expected, corrosion increases significantly as the temperature isincreased. However, it is important to note that below 9000 F the cor-rosion rate is insignificant.

20

15 - Test duratiom 00 br

Outsidesurface

I'I

0

IInsdesuriace

01900 1000 1100 1200 1300 1400 1500

Temperature, F

FIG. 6. Cormsion Rates Versus Temperature of a Section of 3/16-in. -ODIaconal 600 Tube in a Molten LIF-LiOH Environment.

The impurities sulphate and silica increase the corrosion rate ofmost container materials. It was found that small amounts of sulphateions in the melt increased the corrosion rate significantly in all cases.For some high-iron-content alloys, dissolved silica in the melt alsoincreased the corrosion rate. In the case of Inconel 600, however,silica was found to have little effect on the corrosion rate. This isimportant because many of the insulating materials contain silica, andInconel 600 appears to be the best containment material. Sulphur-

10

bearing compounds in insulating materials are suspected of causingcatastrophic failures of test containers on several occasions. The ex-planation is that nickel is subject to attack by sulphur gases at tem-peratures above 600 to 7000F. Reducing conditions are worse thanoxidizing ones and, at temperatures above 11900F, a eutectic of nickeland nickel sulphide forms. Being molten, the eutectic penetrates thegrain boundaries and leads to disintegration of the metals.2

SALT CHARACTERISTICS

A contract was let to the Dynamic Science Corp. , Monrovia, Cali-fornia, to determine the thermodynamic characteristics of the salt. Aparallel effort was conducted in-house to determine the physical charac-teristics of the salt and to check the results of the thermodynamic study.Table 1 lists the basic properties of the salt, as determined by thesetwo studies.

TABLE 1. Properties of Salt Used in Heat Storage

Composition .............................. 205 LiF - 80% LiOH(eutectic mixture)

M elting point ......................................... 800°FVolume change (70 to 1200 0F) ............................ = 7%Density .................................... 90 lb/ft3 at 1200-F

97 lb/ft3 at 70°FAverage specific heat:

Solid ....................................... 0.51 Btu/lb/OFLiquid ...................................... 0.39 Btu/!b/F

Heat capacity from 300 to 1200°F:Solid ........................................... 260 Btu/lbFusion ......................................... SO0Liquid ......................................... 170

Total ....................................... 930 Btu/lb

An important feature of the properties is that the salt density isonly 40% greater than that of water. Hence the space-weight penaltypaid to make the system neutrally buoyant is not as great as for otherenergy sources, for which containers, pumps, plumbing, pressurevessels, and other heavy components require large quantities of flota-tion material to make the system neutrally buoyant.

2 Intemational Nickel Co., Inc. Nickel and Nickel Base Alloys. Huntington, Virginia,

International. (Technical Bulletin T-13.)

° 11

Enthalpy. Figure 7 gives a better idea of the enthalpy distributionfor the salt. It is significant to note that 87% of the total enthalpy inthe range of 300 to 12000 F exists below 900 F. Thus the salt could beused at temperatures below I200F without incurring a severe penaltyin usable enthalpy. It is also significant that more than half of thethermal energy within this range is in fusion at 8000 F. The heatcapacity of the mixture was measured by means of an ice calcrimeter.

Thermal Conductivity. Figure 8 shows the results of studies ofsalt thermal conductivity in the solid state. The conductivity of theeutectic is slightly lower than those of Lif, LiOH, or LiH. However,the net thermal impedance of the LiF-LiOH mixture may be lowerbecause the eutectic adheres to the heat-transfer surfaces withoutforming the voids that often occur in salts having high contraction dur-ing freezing.

CHANGE IN MELTING POINT

When the molten salt is maintained at high temperatures for ex-tended periods, some of the salt decomposes. This decomposition isdue to the breakdown of the LiOH to Li 2 0 and H20. The rate of thisbreakdown is greatly increased by corrosion and by the contaminationof the salt by corrosion products. The breakdown occurs more rapidlyin small containers because of the small ratio of salt volume to con-tainer surface area. Since the surface area varies as the square ofthe container radius, and the volume as the cube of the radius, therate of corrosion and decomposition would be expected to decreasewith large thermal storage units.

Decomposition of the salt changes the melting characteristics andraises the temperature at which the thermal energy is released uponsolidifying. As decomposition proceeds, portions of the salt solidifyat temperatures above 800 ° F. Figure 9 shows an example of the ef-fects of this decomposition, which occurred when some of-the salt wasmaintained at 1200°F for extended periods of time in a small container.

At lower temperatures, corrosion and salt breakdown are greatlyreduced. Tests conducted for long periods at 900 F yielded little orno change or distortion of the melting point. This was the case evenwhen 304 stainless steel was used as the container material.

12

1,200

Average Cp p 0.39 Btu/ lbPF

1,000

80 I

500 Bt/ lb~600

32200 Average C p = 0.51 Btu/lb/ F

0-.0 200 400 600 800 1000 1200 1400

Temperature, F

FIG. 7. Enhalpy Distibution for the LIF-LiOH Eutectic Mixture.

oo

700

600

Sw

S300

200

0 Conp0rl -- technique

iO 0 Cyliider method

0-

0 1.0 2.0 3.0ThumI Comdct~wfty. Sea/ f.-f,.,F

FIG. L Thermal Cawk. tIt Aw tshe LWUX4 btwctk Miae.

13

, -!

1200

Tettm 385 hrI

,, 1000 - • Test time= 3 hr

800

I-

600 LIF-LiOH eutectic mixture

Volume area 0.93 in3 in2

0 so 100 150

Cooling Time, mnn

FIG. 9. Natural Cooling Curves Showing Distortion of the Energy Distribution Resulting

From Extended Test Periods at 12000F. Small test crucibles were used.

WATER SOLUBILITY IN THE EUTECTIC MIXTURE

The original system to which the salt was to be applied called for apressure-balancing concept to eliminate the need for a heavy pressurevessel (see schematic). As the vehicle depth increases, more wateris forced into the inlet tube and is turned to steam, until the pressureabove the salt mass equals the ambient pressure of the ocean. Whenthe vehicle moves to shallower depths, the excess high-pressure steamis expelled from the salt tank and condensed, so that the pressurebalance is maintained at all times.

SteamSalt

Prssr-balance tube

14

Although this pressure-balancing system offers a very simple 4approach to some buoyancy and structural problems, the solubility ofwater in the salts is great enough to impose problems with buoyancycontrol. Data from one experiment, conducted by Atomics Internationaland pertaining to the solubility of water in the salt, are given in Table 2.In general, it was ascertained that water is more soluble in the moltensalt than in the solid, but that the solubility decreases as the tempera-ture is increased above the melting point.

TABLE 2. Sohbility of Water in theEutectic Mixture of LIF-LiOH

Phase Temperature, Preeure, Sohbility,F pu g/ l00g of sak

Solid 800 1,000 2.4

Liquid 806 800 4.7

Liquid 1382 2,000 0.6

Several hours were required for the dissolution of the water to reachequilibrium solubility in this experiment. Upon freezing, however, thedissolved water was expelled rapidly from the melt. This rapid expul-sion caused the salt to expand. When the melt was saturated with waterimmediately above the melting point, the expansion often exceeded theoriginal volume of the melt.

This expansion phenomenon also occurred, but to a much lesser de-gree, whenthere was no steam or high pressure above the salts. Thecause is presumed to be the release of dissolved gases in the salt. Theexpansion is dependent upon the rate of cooling. It was never witnessede iring the tests in which the salt was allowed to cool slowly, but was easyto reproduce under rapid cooling conditions. Figure 10 shows a specimenthat expanded when molten salt was poured into a cold iron mold. Themolten salt had not been exposed to high pressures or a steam atmosphere.

CONCLUSIONS

The work conducted at the Naval Undersea Warfare Center hasyielded data on a eutectic salt mixture with novel characte:zitics thatshruld prove useful in both underwater and other thermal storage appli.cations. The significant characteristics of the lithium fluoride-lithiumhydroxide mixture are as follows-

Is

-- m nn uumrum unn uu m u uu up s ulul~miu n| uu I

.M

FIG. 10. Expansion of the Salt Mixture Resulting From the Release of Dissolved GasesWhen the Salt Was Cooled.

1. Little or no volume change during fusion, and only about 7%volume change over the range from room temperature to 12000F

2. Low melting point of 8000 F

3. Good thermal capacity

4. Relative safety except for normal high-temperature hazards

5. No violent chemical reaction with water

6. Corrosivity with most container materials above 9000 F, but with800 Btu/lb of useful heat capacity available at temperatures be-low 9000 F

16

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I. SP~oT TITLE

EUTECTIC MOLTEN SALT THERMAL STORAGE SYSTEM

4. DICMPTIVO bOm (Tipm SE fteaw i e ) -d

Research report, 1964 through 19665- AuYNO1) aL - 5me. m.s. W.M

Drage, Gary D., DeVries, Gerrit, and Karig. H. E.

5. OU ~ September 1968 M ONone b. 4U 4 P

0. cdwtUAct* .a6To. 'Bureau o Naval S. of 'omI& , ftpONT N O9M

Weapons Task Assignment ASW 202-& '~'*'.. 000/Z16-i/F108-01-33 NUWC TP 74

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and each transmittal to foreign governments or foreign nationals may be madeonly with the prior approval of the Naval Undersea Warfare Center.

,I. o-0% T 1= fto . ,pM~m, UTAOY ACTIIYM

Naval Ordnance Systems CommandNaval Material CommandWuKAhinttLnB fl C 1.0360

IS. A11810ACT

An analysis of various thermal storage materials indicatedthat a eutectic mixture of lithium hydroxide and lithium fluoridewould provide relatively high heat capacity for a closed-cyclethermal propulsion system for deep-running underwater vehicles.In contrast with other high-heat-capacity lithium compounds.this eutectic nii bre undergoes practically no expansion duringfusion. It has a low melting point of 800r. It does not reactchemically with water, but does al sorb small amounts of waterif directly exposed to steam at hith pressure. LiF-LiOH cor-rosion tests on samles of various metals, incivAtiag 304 stainle. vsteel and Inconel 60Q, indicated that corrosion ny oIcur atrandom at .'mperattres above 900+T. From 900VF to 12004F.Incose- 600 indicated tka least corrosion of any high-strengthmaterial tested.

DD t.at!'L 1473 .. s U?4CLASSIFIED

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UN LASqTF1r-nSecuity Classification _____ ____

KE WRD LINK A LINKS 9LNK C______________________________________ ROLE___ WT ROLE MIT ROLE WT

Power plantsThermal energyClosed-cycle systemsEutectics

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7b. NUMBER OF REFERENCES: Enter the total nuber of It in highly desirable that the abstract of classified reportsreferences cited in twhepL b e unclassified. Each paragraph of the abstract shall end withG&. CONTRACT OR GRANT NUER: It oppropriste, efter an Indication of abs military security classification of the In-the applicable number of the contrsct or peant iwader which formation in the paragraph, represented as (Ta). (s.), (c). or (U).the repot m written. Tere is no limitation on the length of the abstract. How-$6.ft & k S PROJECT NUMBR: Enter thw appropriate ever, the suggested length Is from 130 to 225 words.mUllly dop umet Identification. such s prjc wodsaeuehnbere.igfltemsub *)ect a uber, system masher., task nunbr, atc. 14. KEY WORDS:, Keywr*o*tehial eaigu em

or short phrases that charace rice a report sand may be ueed an9&. CARICPMATOR'S RPOT NWU(o) Enter the offi index entries for cata losing Mhe report Key words must becis[ P, -wct ember by which the document will he Identified selected so that no security classification Is required. Identi-and c..j*olled by the originating activity. This number m=st flere. such as equipment model designation, trade name, militarybe aw. pe to thin report. project code name, geographic location, may be us"d as key9b. 0TWILR REPORT NUM8RR()- If the repot has bee words but will he followed by an indication of technical con-assigned say othor repor numbers (either by tihe oEdjinaior tast. The assignmenft of links, rules, and weights In optional.or by Mhe apsoe.) ale* enter this ambor(s).I10. AVAU..ABaLZT/LIITATO N 01 oTICES: Enter any Jim-Itations en frther lisemaintioa of the report, other thes thoe__

* UNCLASSIFIEDSecurity Classificationi