冰浆管内流动的融化传热特性

1、HeattransfercharacteristicsoftheiceslurryatmeltingprocessinatubeowDongWonLee*,EungSangYoon,MoonChangJoo,AtulSharmaNewandRenewableEnergyResearchDepartment,KoreaInstituteofEnergyResearch,71-2,Jang-dong,Yusong-gu,Daejon,305-343,SouthKoreaReceived30March2005;receivedinrevisedform22August2005;accepted7Oc

2、tober2005Availableonline20December2005AbstractTheheattransfercharacteristicswereexperimentallyinvestigatedforiceslurrymadefrom6.5%ethyleneglycolwatersolutionowina13.84mminternaldiameter,1500mmlonghorizontalcoppertube.Theiceslurrywasheatedbyhotwatercirculatedattheannulusgapofthetestsection.Experiment

3、softhemeltingprocesswereconductedwithchangingtheiceslurrymassuxandtheicefractionfrom800to3500kg/m2sand025%,respectively.Duringtheexperiment,itwasfoundthatthemeasuredheattransferratesincreasewiththemassowrateandicefraction;however,theeffectoficefractionappearsnottobesignicantathighmassowrate.Atthereg

4、ionoflowmassowrates,asharpincreaseintheheattransfercoefcientwasobservedwhentheicefractionwasmorethan10%.q2005ElsevierLtdandIIR.Allrightsreserved.Keywords:Iceslurry;Flow;Tube;Experiment;Heattransfer;Masstransfer;Melting´coulementalinte´rieurdetubes:caracte´ristiquesCoulisdeglaceenedetr

5、ansfertdechaleurlorsdelafusion´coulement;Tube;Expe´rimentation;Transfertdechaleur;Transfertdemasse;Fusion´s:Coulisdeglace;EMotscle1.IntroductionThecoldheatstoragesystemforairconditioninghasbeendevelopedforthepurposeofsavingenergyandreducingthepeakelectricaldemandinthedaytimeduringsumm

6、er.Inparticular,agreatdealofattentionhasbeenpaidtotheicestoragesystemsinceitwouldbebenecialto*Correspondingauthor.Tel.:C82428603530;fax:C82428603538.E-mailaddresses:dwleekier.re.kr(D.W.Lee),atul_sharma2(A.Sharma).utilizethelargelatentheatofmeltingice.Amongthemanyicestoragesystems,iceslurrytypestorag

7、esystemhasbeenconsideredbecauseithasmanymerits1,2.Inrecentyears,however,therearemanyattemptstouseiceslurryasacoldheattransfermediumfordistrictcoolingorasecondaryrefrigerantinconventionalcoolingprocessessinceitcanbepumpeddirectlythroughdistributionpipeworksandheatexchangers.Theiceslurryasthealternati

8、veofthesingle-phasesecondaryrefrigerantslikebrineoffersseveraladvantages.Firstofall,theiceslurryisusefulforthefutureofrefrigerationwithacontextofozonedepletionandglobalwarming.Referringtothecharacteristicsofice452D.W.Leeetal./InternationalJournalofRefrigeration29(2006)451455slurry,itcanbeeasilypumpe

9、dthroughtransportationpipesandheatexchangers24,moreoverthecoldheatcapacityoficeslurryismuchgreaterthanthatofconventionalsingle-phasesecondaryrefrigerantsbecauseofthephasechangeenergyoftheiceparticles.Concerningthecoldheatremovalfromtheiceslurry,thehighheattransfercoefcientoficeslurryowanditslargecoo

10、lingcapacityinaheatexchangerallowthereductionintheheatexchangersize,thestabilizationofextractiontemperatureataroundameltingpointanditsquickresponsetothethermalloaddemand.Therefore,pipedimensions,pumpingenergy,heatexchangersizeandoperatingcostscouldbereducedsignicantly5,6.Anotheradvantageoficeslurrys

11、ystemsisthattheuidcanbecompletelysafeandharmlesstotheenvironment.Theseadvantagesmakeiceslurrysystemsveryattractivefromboththetechnicalandeconomicviewpoints.Todevelophighefciencycompactheatexchangersforiceslurryapplications,basicdataontheheattransfercharacteristicsoficeslurryarerequired.However,littl

12、eisknownaboutmeltingheattransfercharacteristicsoficeslurriesinheatexchangers.Jensenetal.7andSarietal.8reportedanincreaseintheheattransfercoefcientwithincreasingicefractionandowrateinaheatexchanger.Ontheotherhand,SnoekandBellamy9andKnodeletal.10showedthattheheattransfercoefcientdecreaseswithincreasin

13、gicefraction.Thesediscrepanciesintheheattransferresultsindicateadifferentbehavioroftheiceslurriesatdifferentowraterange,iceparticlesizeandsolutionconcentrations.Worksinexplainingthesedifferentbehaviorsarenotentirelyconcluded.Thus,itisrequiredtoclarifythefundamentalheattransfermechanismoficeslurryund

14、ervariouspracticalconditionsforindustrialcoolingprocess.Severalstudiesofneparticleiceformationonacoolingwallhavebeenperformedusingaqueoussolutionsorsomeadditivesconcernedwithcoldpreserving2,1115.Correspondingwithnaturalconvection,iceremovalconditionsofethyleneglycolaqueoussolutiononvariouscoolingwal

15、lswereobservedbyHirata16.Alcoholicmaterialssuchasethyleneglycol,propyleneglycolandethanolarewellknownasbrines,whicharenotonlyeasytomixinwater,butalsohavewell-openedproperties.Ethyleneglycolconsistsofhydroxylandethylene,thehydroxylpartbondswithinorganicmaterialorwatermolecules.Incontrast,theethylenep

16、artwithhydrophobicmaterialdisplacestotheemptyspacebetweenwatermolecules.Thus,ethyleneglycoldisperseswellinwater17.Duetothesemerits,theethyleneglycolsolutionusedfortheiceslurrymakinginthepresentstudy.Thepurposeofthisstudyistoexperimentallyinvestigatetheheattransfercharacteristicsforiceslurrymadefrom6

17、.5%ethyleneglycolwatersolutionbyacommercialiceslurrygeneratorowinginthecircularpipes.Theinuencesofmassuxandicefractionontheheattransfercharacteristicswereinvestigatedandthustoprovidefundamentalinformationforthecoolingheatexchangerusingiceslurryasasecondaryrefrigerant.2.ExperimentalapparatusTheschema

18、ticdiagramofexperimentalapparatusisshowninFig.1.Theapparatusconsistsofaniceslurrygeneratorandicestoragetank(2m3),ahotwaterbathwithconstanttemperature,watercirculationpumpandanotherpumptocirculatetheiceslurrytothetestsection.Thetestsectionisahorizontaldoubletubeheatexchangerof1500mminlength.Iceslurry

19、owsinaninsidecoppertube(13.84mmID)andhotwatercirculatesinanannulargapbetweentheinsideandoutside(25mmOD)tubes.CorrectedfourRTD(accuracyG0.058C)areusedtomeasuretheinletandoutlettemperatureoftheiceslurryandthehotwater.SixK-typethermocouples(0.2mmFig.1.Schematicdiagramoftheexperimentalapparatus.D.W.Leee

20、tal./InternationalJournalofRefrigeration29(2006)451455453ODandaccuracyG0.28C)placedinordertomeasurethewalltemperatureoftheinnertubeoftheheatexchanger.Thus,theaveragelocalheattransfercoefcientcouldbedeterminedbyusingthemeasuredheatux(accuracyG3%)andaverageofthesewalltemperatures.Themassowrateanddensi

21、tyoficeslurryattheinletandoutletofthetestsectionweremeasuredbyuseofmassowmeter.Themagneticowmeterwasusedtomeasuretheowrateofhotwaterwithuncertaintyofabout1%.TheentirepipeworkandthetestsectionarewellinsulatedusingArmaexinsulatingformtopreventtheheatlossandheattransferacrossthewallstotheambientwasnegl

22、ected.Agilent34970Adataacquisitionsystemwasusedformeasurementandrecordingofdata.Thedataarerecordedwith4sintervals.3.Experimentalprocedure6.5%EthyleneglycolwatersolutionfromthebottomofthestoragetankowedintotheiceslurrygeneratorwhichismadebyDYKoreancompanyandapartofthesolutionchangedintoiceparticlesan

23、dtherestofthesolutionwasrecycled.Avariablespeedagitatorwasusedtomaintainauniformicefractioninthestoragetank.TheiceslurrygeneratorproducediceparticlesofnesizeefcientlyasshowninFig.2.Themeandiameteroftheiceparticleswasestimatedtobeis0.27mmbyassumingalltheparticlestobeinasphericalform.Theexperimentsare

24、performedusingthefollowingprocedure.Initiallyiceslurrywasproducedusingthegeneratorandstoredinthestoragetank.Asthegeneratorcontinuedtoproduceiceparticles,theicefractioninthestoragetankincreased.Oncethepercentageoficefractioninthestoragetankreachedanddesiredvalue(above25%),theslurrygenerationsystemwas

25、shutdownandtheagitatorinsidethetankwasoperated.Thisallowedgoodmixingofthebrinesolution,producingahomogeneousmixturethroughouttheexperiment.Theicefractioninthestoragetankcouldbemeasuredbysupplyingtheiceslurrytothemassowmeterinstalledintestsection.Thehotwatermaintainedataprescribedtemperatureandthenci

26、rculatedtothetestsectionwithgivenowrate.Afterthat,iceslurrywascirculatedtothetestsectionattheprescribedmassowrate.Duringthetesttheicefractioninthestoragetankdecreasedgraduallyduetotheheattransferredbythehotwater.Thisprocedureproducedheattransferdataforiceslurryfromtheinitial25%icefractiontozeroinasi

27、ngletestataprescribedmassuxcondition.Sameexperimentsofthisprocedurewithdifferenticeslurrymassuxwereconductedoverarangeof8003500kg/m2s.Toseetheeffectofthehotwatertemperatureontheheattransfercoefcientswith1000and2000kg/m2siceslurrymassux,twoanothersetofexperimentshasbeenconducted.Thehotwatertemperatur

28、esduringtheseexperimentswereoverarange7.522.58C.Adatascanconsistedofasetofreadingsofalloftheinstruments:owmeters,RTD,thermocouplesetc.Theamountoftheheattransferredfromthehotwatertotheiceslurryiscalculatedwiththedifferencebetweentheinletandoutlettemperaturesandowrateofthehotwater.Thedatathatarerequir

29、edfortheassessmentoftheheattransferwerecollectedat4sintervals.Inordertoachieveusefulresultsineveryexperiment,thedatahavebeencollectedcontinuouslyduringtheexperiment.Andmeanvaluesofthedataover510minperiodamongthecollecteddataweretreatedthenalvaluesusedintheanalysis.4.ResultsanddiscussionTocomparethei

30、nternalheattransferrateandheattransfercoefcientsoficeslurryatvariousconditions,datareductionwasperformed.Theheattransferratewasobtainedfromtheinletandoutlettemperaturesandowrateofthehotwater.Theaverageheatuxcouldbecomputedbydividingtheheattransferratebythesurfaceareaoftheinnertubeincontactwiththeice

31、slurry.Andtheheattransfercoefcientwasevaluatedbydividingtheheatuxbythedifferenceintheaveragedwalltemperaturemeasuredbysixthermocouplesandiceslurrytemperature(averagevalueoftheinletandoutlettemperatureofthetestFig.2.Iceparticlesandtheirdiameterinthisstudy.454D.W.Leeetal./InternationalJournalofRefrige

32、ration29(2006)451455section)duringthemeltingexperimentassumingaconstantheatuxovertheentiretubesurface.Fig.3showstheeffectofthemassuxandicefractionoficeslurryontheheattransferrateatthehotwatertemperature(10.58C)andowrate(20L/min)conditions.Asexpectedtheheattransferrateincreaseswiththemassux.Asshownin

33、thisgure,theheattransferrateincreaseswithincreasingicefraction,indicatingthattheheattransferoficeslurryincreasescomparedtotheconvectionheattransferforsinglephasewatersolution,asmoreiceparticlesarepresentintheiceslurry.However,thisgureclearlyshowsthattheeffectoficefractionismoresignicantatlowmassuxra

34、nge.Thatis,theheattransferrateincreasesgraduallywiththeicefractionathighmassuxrange,butsharpincreaseintheheattransferrateoccurredatlowmassuxrange.Fig.4showstherelationshipbetweentheheattransfercoefcientandtheicefractionwithvariousiceslurrymassuxatthesameconditions.Atlowmassuxrange,itcanbeseenfromthe

35、gurethattheheattransfercoefcientdidnotchangewithicefractionuntilitreachedtocertainicefractionvalue(about10%inthiscondition).However,asharpincreaseintheheattransfercoefcientoccurredattheicefractionabovethispoint.Instead,theheattransfercoefcientincreasesgraduallywiththeicefractionatthehighmassuxrange.

36、ThesimilartendencywasobservedatthepreviousworkgivenbyLeeetal.18,whichinvestigatedthepressuredropcharacteristicsoficeslurry.Inthatstudy,asharpincreaseinthepressuredropwasfoundattheicefractionabovecertainpointwithhorizontalpipe.Thusthecharacteristicsoftheheattransferoficeslurrymaybeexplainedintermsoft

37、hefactthattheheattransferisstronglyaffectedbythefrictionbetweentheiceparticlesandthepipewall.ItisexplainedbyconsideringthattheturbulenceinthermalboundarylayerduetotheiceparticlesandthelatentheatoficemeltingeffecttheheattransfercoefcientsFig.3.Heattransferratevs.inleticefractionfordifferenticeslurrym

38、assux.Fig.4.Heattransfercoefcientsvs.inleticefractionfordifferenticeslurrymassux.betweenthepipeandtheiceslurry.Thatis,theheattransferrateincreasesbecauseoatingiceparticlesinthepipedisturbthethermalboundarylayeratthelowmassuxrange.However,theextentoftheincreaseoftheheattransferratedecreasesasthemassu

39、xincreased,thereasonbeingthaticeslurrybehavedlikehomogeneousliquid.Fig.5showstheeffectofthehotwatertemperatureontheheattransfercoefcientsfordifferentmassux(G,1000and2000kg/m2s).Theresultsindicatethat,atagivenmassux,theheattransfercoefcientsareapproximatelythesameirrespectiveofthehotwatertemperaturei

40、nspiteoftheheattransferrateincreaseswithhotwatertemperature.Thisyieldstheaccuracyoftheexperimentsanddatareducingprocess.FromtheFigs.35,itisclearthatthattheeffectofthevariationoftheicefractionandthesizeoftheiceparticlesappearedsimultaneously.Inthecaseoficeslurrymovingthroughaheatexchanger,increasedhe

41、attransfercoefcientoftheiceslurryisdesirablebecauseitleadstosignicantreductionsinboththesizeoftheheatexchangersandpumpingpower.Fig.5.Heattransfercoefcientsvs.inleticefractionfordifferenthotwatertemperatures.D.W.Leeetal./InternationalJournalofRefrigeration29(2006)4514554555.ConclusionsTheheattransfer

42、characteristicsoficeslurrymadefrom6.5%ethyleneglycolwatersolutionmadebyacommercialiceslurrygeneratorwereexperimentallyinvestigatedandthefollowingconclusionsweredrawnwithintheparameterrangecoveredinthepresentstudy.Theheattransferrateincreasesasthemassuxoficeslurryincreases.Heattransfercoefcientwashig

43、hwiththeiceslurriesascomparedtoliquidwatersolutionowingatthesamemassux.Asharpincreaseintheheattransferoccurredaticefractionslargerthanabout10%atthelowmassuxrange.However,atthehighmassuxrange,theheattransferincreasedgraduallywiththeicefraction.Otherinvestigatorshavereportedeitherincreasingordecreasin

44、gheattransfercoefcientswithincreasingicefraction.Thisindicatesthattheinuenceoficefractionontheheattransfercoefcientisafunctionoftheiceparticlesize,theowrate,thepipesize,thekindofsolutionandetc.Furtherworkisrequiredtoquantifytheeffectoftheseparametersontheheattransferoficeslurry.AcknowledgementsTheex

45、perimentsofthisstudywereperformedatKoreaInstituteofEnergyResearchwiththesupportoftheKEMCO.References1Z.Ure,M.Mashrae,Slurryicebasedcoolingsystems,ProceedingsofIIR20thinternationalconference,vol.5,1999Paperno.3.2A.Saito,Recentadvancesinresearchoncoldthermalenergystorage,IntJRefrigeration25(2002)17718

46、9.3T.M.Hansen,M.Kauffeld,O.Sari,P.W.Egolf,F.Pasche,Research,developmentandapplicationsoficeslurryinEurope,Proceedingsofthefourthworkshoponiceslurriesoftheinternationalinstituteofrefrigeration,Osaka,2001,p.112.4S.Fukusako,M.Yamada,T.Kawanami,Systemandcomponentsforcoldthermalstoragewithslushice,ThermS

47、ciEng6(1998)169178.5P.Metz,P.Margen,Thefeasibilityandeconomicsofslushicecoolingsystems,ASHRAETrans932(Part2)(1987)16721686.6H.Inaba,Newchallengeinadvancedthermalenergytransportationusingfunctionallythermaluids,IntJThermSci39(2000)9911003.7JensenEN,ChristensenKG,TorbenHM,SchneiderO,KauffeldM.Pressuredropandheattransferwithiceslurry,IIFIIRCommissionB1,B2,E1,andE2forPurdueUniversity;2000,p.52128.8O.Sari,F.Meili,D.Vuarnoz,O.W.Egolf,Thermodynamicsofmovingandmeltingiceslurries,Proceedingsofthe2ndIIRworkshoponice