ht materials-phase change

8/12/2019 HT Materials-Phase Change

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AShortCoursebyRezaToossi,Ph.D.,P.E.CaliforniaStateUniversity, LongBeach

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PhaseChangeMaterials Applications

Properties

Modeling

MeltingandSolidification

Evaporation

AerosolJetImpingement

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Abhat,A.,Lowtemperaturelatentheatthermalenergystorage:heatenergystoragematerials,SolarEnergy,30(1983)313332.

Exothermic(warmingprocesses) Melting

Point(oC)LatentHeat

Density(kg/m3)

on ensat on Steamradiators

Freezing Orangegrowerssprayorangeswithicedwater

Deposition Snowydaysarewarmerthancleardaysinthe

winter

Endothermic(coolingprocesses) Evaporation/Boiling

Steel 1400 247 7800

Copper 1086 206 8900

Ice 0 335 917

SodiumSulfate

32 252 1495

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weat

Alcoholiscool

Melting Meltingiceindrinks

Sublimation Coolingwithdryice


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SolidLi uid Temperaturecontrol

Ablation

Coating

LiquidVapor vaporat vecoo ng

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EnergyStorageinBuildings

Passiveheatingandcooling

ThermoelectricRefrigeration

Transportoftemperaturesensitivematerials ThermalControl

IndustrialForming(casting,laserdrilling)

FoodandPharmaceuticalProcessing

TelecomShelters

Humancomfortfootwearandclothes

ermosan coo ers

ElectricalGeneration Cogeneration

ThermoelectricPowerGeneration

SecurityofEnergySupply Flowthroughheatexchangers

MicroencapsulatedPCMs

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Thermod namicCriteria

Ameltingpointatthedesiredoperatingtemperature

Ahighlatentheatoffusionperunitmass

Ahighdensity

Ahighspecificheat

Congruentmelting

Smalldensitydifferencesbetweenphases

Littlesupercoolingduringfreezing

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ChemicalCriteria Chemicalstability

Noncorrosive,nonflammable,nontoxic Others Longshelflife

A licabilit

Reliability Commercialavailability

Lowcost

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Withoutenca sulation containersha eandmaterial)

Encapsulation Buildingmaterials(PCM5080%,unsaturatedpolyester

matrix4510%,andwater510%)

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Availabilit ofsmallnumberofmaterialsinthetemperaturerangeofinterest

UsefullifeMaintenanceStability

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OrganicCompounds Paraffins

FattyAcids

SaltBasedCompounds SaltHydrates

Eutectics Others Iceandwater

Zeolite

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Advantages Awiderangeofmeltingpoints

Nontoxic,noncorrosive

Chemicallystable

Compatiblewithmostbuildingmaterials

Highlatentheatperunitmass

Meltingcongruity

Negligiblesupercooling

Areavailableforwiderangeoftemperatures

Expensive

Lowdensity

Lowthermalconductivity(comparedtoinorganiccompounds)

Largecoefficientofthermalexpansion

Flammable

Donothaveawelldefinedmeltingtemperatures.

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Advanta es Lowercost

Highlatentheatperunitmassandvolume

Highthermalconductivity

Widerangeofmeltingpoints(7117oC)

Disadvantages Highrateofwaterloss

Corrosive

Phaseseparation

SubstantialSubcooling

Phasesegregation(lackofthermalstability)

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Coolin 1 oC)TemperdiurnalswingsHeatpumpsSolarhotwaterheatingsystemsAbsorptionairconditioner

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Roof

Wall

Window

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Velraj,R.,andPasupathy,A.,PHASECHANGEMATERIALBASEDTHERMALSTORAGEFORENERGYCONSERVATIONINBUILDINGARCHITECTUREInstituteforEnergyStudies,CEG,AnnaUniversity,Chennai 600025.INDIA.

Basedon m2 ofsolarcollectorarea

TES Systems Cost($) Volume(m3)

Water 54 0.72

Rock 217@$8/ton 2.46

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Glaubers Salt 146 0.18


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ConventionalCD(readonly)CDR(recordable)CDRW(readandwrite)

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Sodiumacetate trih drate) Tsl =54

oC

hsl =1.86x105 J/kg

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MeltingofSolids

Boiling FilmBoiling

PoolBoiling

Condensation FilmCondensation

DropwiseCondensation

eroso e pray Nucleation

Impingement

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Oneregion

Multipleregion

Tworegion

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ContactMelting(meltingofasolidunderitsownweight)

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Solid Scaleanalysis

Liquid

B.C

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Governing Equations (Neumannproblem):

BoundaryConditions

Solution:

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Analytical 1Dandsome2Dconductioncontrolled

Strong(Classical)numericalsolution Velocityu andpressurep satisfyNavierStokesequationspointwisein

spacetime.

Weak(FixedGrid)solution EnthalpyMethod(Shamsunder andSparrow,1975)

e qu va en ea apac y e o onac na e a .,1973 TheTemperatureTransformingModel(CaoandFaghri,1990)

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TwoRegionMeltingofaSlab Assumedensitiesoftheli uidandsolid hasearee ual.

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1. ChoosetandxtomeetNeumannsstabilitycriterion

2. Determinetheinitialenthalpyateverynodehjo (j=1)

3. Calculatetheenthalpyafterthefirsttimestepatnodes(j=2,...,N 1)byusingequation(1).

4. Determinethetemperatureafterthefirsttimestepatnode(j=1,...,N)byusingequations(2)and(3).

5. Findacontrolvolumeinwhichtheenthalpyfallsbetween0andhsl ,anddeterminethelocationofthesolidliquidinterfacebyusingequation(4).

6. Solvethephasechangeproblematthenexttimestepwiththesameprocedure.

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Unconditionallystablebutismorecomplexecause woun nownvar a esen a pyan

temperatureareinvolved.[SeeAlexiades, A.,andSolomon,A.D.,1993,MathematicalModelingofMeltingandFreezingProcesses,Hemisphere,Washington,DC.]

Transformtheenergyequationintoanonlinearequationwithasinglevariableh.[SeeCao,Y.,andFaghri ,A.,1989,"ANumericalAnalysisofStefanProblemofGeneralizedMultiDimensionalPhaseChangeStructuresUsingtheEnthalpyTransformingModel,"InternationalJournalofHeatandMassTransfer,Vol .32,pp.12891298.]

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3DConductioncontrolledmelting/solidification

Heatcapacityduringthephasechangeisinfinite. AssumeCp andkchangelinearlyfromliquidtosolid

Advantage:Simplicity Disadvantage:

Unstableifrightchoicesforx,t,andTarenotmade.

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Combinationofthetwomethods[Cao,Y.,andFaghri ,A.,1990a,"ANumericalAnalysisofPhaseChangeProblemincludingNaturalConvection,"ASMEJournalofHeatTransfer,Vol .112,pp.812815.]

UsefinitevolumeapproachbyPatankar tosolvethediffusionequation.

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Assumptions EnthalpyMethodapproachisconsidered

Newtonianincompressiblefluidwithconstantproperties,exceptthedensitythatisevaluatedslinearfunctionoftemperature(Bousinessqapproximation)

Effectiveconductivityinthemushyzone

Isotropic

Heattransferbyconduction,convectionand

43CARLOS HERNNSALINASLIRA1,SOLIDIFICATIONINSQUARESECTION,Theoria,Vol.10:4756,2001.

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EulerianAveraging Avera edovers ace time orbothwithinthedomainofinte ration

Basedontimespacedescriptionofphysicalphenomena

Consistentwiththec.v.analysisusedtodevelopgoverningequations.

Euleriantimeaveraging

Eulerianvolumeaveraging

Phaseaverages: Intrinsicphaseaverage

Extrinsicphaseaverage

agrang an verag ng Followaparticleandaverageitspropertiesduringtheflight

MolecularStatisticalAveraging Boltzmannstatisticaldistributionratherthanindividualparticleisthe

independentvariable.

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Governing Equations:

Jany,P.,andBejan,1988,"ScalingTheoryofMeltingwithNaturalConvectioninanEnclosure,"InternationalJournalofHeatandMassTransfer,Vol.31,pp.12211235.

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Nucleation Homogeneous

Heterogeneous Filmwise

Dropwise

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Liquidandgasproperties , lg

Surfacetensionattheinterface,Phasedensitydifference,(l g)SurfaceroughnessandorientationContactangle,

c

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InspiredbyNamibdesertbeetleMimicswingwithamicroscopic

patternofwaterattractingandwaterrepellingareas

Alsoseenonlotusleaves

ApplicationsincludeSelfdecontaminatin surfaces

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AntifoggingsurfacesMicrofluidicchips

HarvestingdewsasdrinkablewaterPocketsizedchemicaltestingdevices

video.mpg

RubnerandCohen,NanoLetters6(6),12131217(2006)

Nanostructuredfilmmadeofalternatinglayersofpositivelyandnegativelychargedpolymersandsilicananoparticles

Dualqualitymaterialcanbepatternedtorepelwaterin

someareas sp er ca droplets)andattractitinothers(flattenedones).

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Thet eofboilin de endson PoolBoiling(waterinapanontopofastove)

Subcooled(local)Tliq


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Effectofsubstrate(Layeredstructureofanelectricheater)

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enhancedwallfunction Macroscale(jetflow) Microscale(dropletdynamics)

Impactofsingledroplet

Impactofmultipledroplets

Garbero,etal.,Gas/surfaceheattransferinspraydepositionprocesses,Intl.J.HeatandFluidFlow,Vol.27,Issue1,Feb2006,pp.105122

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Singleroundjet:

Multiplejets:

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SingleDroplet WeD


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B Correlationnumber D jet/nozzlediameter d dropletdiameter K dropletsplashing criterion n numberofdroplets numberfluxofdroplets Nu Nusseltnumber,hD/k Nu0 Nusseltnumberinabsence

o part c es massloading surfacetension

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ComparisonwithparallelflowExample:SubstratecoolingofaplasticsheetL=20cm,Ts =95

OC,Tf,=20OC,

Uf,=5m/sforparallelflow;=25m/sinnozzleFluid:water

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Beforeimpact

AfterimpactDropletdeformation(spreading)duringimpact

(dp = 200m,Up = 10 m/s).

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Contoursoftotalsurfaceheatflux(seenfrombelow)

Velocityvectorsduringtheimpactofthreedroplets:threedroplet

Garbero,Vanni,andFritscling,Gas/surfaceheattransferinspraydepositionprocesses,IntlJ.HeatandFluidFlow,Vol.27,Issue1.Feb2006,pp.105122. 78


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Bai and Gosman (1995): Drop collision model, , , ,

inducedbreakup,Randombreakup,Splash) Wang and Watkins (1990)

We80

Park,K.,andWatkins,A.P.,Comparisonofwallsprayimpactionmodelswithexperimentaldataondropvelocitiesandsizes, Int.J.HeatandFluidFlow,Vol.17,No.4,August1996.

Where,

Cwb =1/3

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Rebound, Rebound with breakup, Break-up, and Splash(Park and Watkins, 1996)

Spreading velocity

Film thickness

SplashingCriteria(Bussmann,2000)K


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For additional questions, Pleaseemail [email protected].

Finnedtubes [1]A.Abhat,S.AboulEnein,N.Malatidis,Heatoffusionstoragesystemsforsolarheatingapplications,in:

. en u en . , erma torageo o ar nergy, art nus o ,19 1. [2]V.H.Morcos,Investigationofalatentheatthermalenergystoragesystem,SolarWindTechnol.7(2/3)

(1990)197202. [3]M.Costa,D.Buddhi,A.Oliva,NumericalSimulationofalatentheatthermalenergystoragesystemwith

enhancedheatconduction,EnergyConvers. Mgmt.39(3/4)(1998)319330. [4]P.V.Padmanabhan, M.V.KrishnaMurthy,Outwardphasechangeinacylindricalannuluswithaxialfins

ontheinnertube,Int.J.HeatMassTransfer29(1986)18551868. [5]R.Velraj,R.V.Seeniraj,B.Hafner,C.Faber,K.Schwarzer,Experimentalanalysisandnumericalmodelling

ofinwardsolidificationonafinnedverticaltubeforalatentheatstorageunit,SolarEnergy60(1997)281290.

[6]R.Velraj,R.V.Seeniraj,B.Hafner,C.Faber,K.Schwarzer,Heattransferenhancementinalatentheatstoragesystem,SolarEnergy65(1999)171180.

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Embedding

in

Graphite

Matrices [7]P.Satzger,B.Exka,F.Ziegler,Matrixheatexchangerforalatentheatcoldstorage,Proceedingsof

Megastock98, Sapporo(Japan),1998. [8]H.Mehling,S.Hiebler,F.Ziegler,LatentheatstorageusingaPCMgraphitecompositematerial:

advantagesandpotentialapplications,Proceedingsofthe4thWorkshopofIEAECESIAAnnex10,Bendiktbeuern(Germany),1999.

[9]X.Py,R.Olives,S.Mauran,Paraffin/porousgraphitematrixcompositeasahighandconstantpowerthermalstoragematerial,Int.J.HeatMassTransfer44(2001)27272737.

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