相變材料微膠囊懸浮液在矩形小通道內(nèi)流動傳熱的實驗研究相變材料微膠囊懸浮液在矩形小通道內(nèi)流動傳熱的實驗研究

摘要：

本研究采用相變材料微膠囊懸浮液作為傳熱介質(zhì)，在微觀尺度的矩形小通道內(nèi)進行了流動傳熱實驗。通過在實驗中改變通道尺寸、相變材料微膠囊懸浮液濃度和速度等因素，探究了相變材料微膠囊懸浮液傳熱性能與流動特性之間的關(guān)系。實驗結(jié)果表明，相變材料微膠囊懸浮液流體的傳熱性能明顯優(yōu)于普通液體，同時隨著通道尺寸的減小和濃度的增加，傳熱效果進一步改善。此外，通過對流體的流動特性進行分析發(fā)現(xiàn)，在流體進口處存在著較為明顯的“矛盾點”現(xiàn)象。本研究為相變材料等非傳統(tǒng)傳熱介質(zhì)在微觀通道內(nèi)的傳熱研究提供了新的參考和思路，具有一定的理論和應用價值。

關(guān)鍵詞：相變材料微膠囊懸浮液、微觀通道、傳熱性能、流動特性、矛盾點

Abstract:

Inthisstudy,aphasechangematerialmicrocapsulesuspensionwasusedastheheattransfermedium,andtheflowandheattransferexperimentswerecarriedoutinamicro-scalerectangularchannel.Bychangingthechannelsize,concentrationandvelocityofthephasechangematerialmicrocapsulesuspensionduringtheexperiment,therelationshipbetweentheheattransferperformanceandtheflowcharacteristicsofthesuspensionwasexplored.Theexperimentalresultsshowthattheheattransferperformanceofthephasechangematerialmicrocapsulesuspensionissignificantlybetterthanthatoftheordinaryliquid,andtheheattransfereffectisfurtherimprovedwiththedecreaseofthechannelsizeandtheincreaseoftheconcentration.Inaddition,itisfoundthatthereisa"contradictionpoint"phenomenonattheinletofthefluidbyanalyzingtheflowcharacteristicsofthefluid.Thisstudyprovidesnewreferenceandideasfortheheattransferresearchofnon-traditionalheattransfermediumssuchasphasechangematerialsinmicro-channels,andhascertaintheoreticalandpracticalvalue.

Keywords:phasechangematerialmicrocapsulesuspension,micro-channel,heattransferperformance,flowcharacteristics,contradictionpoint.Theuseofphasechangematerials(PCMs)hasgreatpotentialforenhancingthethermalperformanceofmicro-channels.However,theflowcharacteristicsofPCMmicrocapsulesuspensioninmicro-channelsarecomplex,andtheheattransfermechanismisstillnotclear.Inthisstudy,weinvestigatedtheheattransferperformanceofPCMmicrocapsulesuspensioninamicro-channelandanalyzedtheflowcharacteristicsofthefluid.

OurresultsshowthattheheattransferperformanceofthePCMmicrocapsulesuspensioninthemicro-channelisaffectedbytheconcentrationandsizeofthemicrocapsules.Astheconcentrationofmicrocapsulesincreases,theheattransferperformancefirstimprovesandthendeterioratesduetotheincreaseinviscosityandthermalresistance.Inaddition,theheattransferperformancealsodecreaseswiththeincreaseofmicrocapsulesize,whichismainlyattributedtothedecreaseofeffectivethermalconductivityofthesuspension.

Furthermore,wefoundthatthereisa"contradictionpoint"phenomenonattheinletofthemicro-channel,wheretheheattransferperformancereachesamaximumvalueandthendecreasesastheflowrateincreases.ThisphenomenonisduetothecompetitionbetweentheeffectsofPCMmicrocapsulesontheconvectiveheattransferandthepressuredrop,whichleadstoatrade-offbetweentheheattransferperformanceandtheflowresistance.

TheanalysisofflowcharacteristicsshowsthatthePCMmicrocapsulesuspensioninthemicro-channelexhibitsdifferentflowregimes,includingsingle-phaseflow,two-phaseflow,andplugflow.Theflowregimeandthedistributionofmicrocapsulesintheflowfieldhaveasignificantimpactontheheattransferperformance.

Overall,thisstudyprovidesnewinsightsintotheheattransfermechanismofPCMmicrocapsulesuspensioninmicro-channelsandoffersguidanceforthedesignandoptimizationofmicro-channelheatexchangersusingPCMmicrocapsules.Inadditiontotheabovefindings,thisstudyalsohighlightssomechallengesandlimitationsofutilizingPCMmicrocapsulesuspensionforheattransferenhancementinmicro-channels.Oneofthemainchallengesisthedifficultyinachievingauniformlydispersedandstablesuspensionofmicrocapsulesintheworkingfluid.Anynon-uniformityoragglomerationofmicrocapsulescanresultinflowinstability,reducedheattransferperformance,andcloggingofthemicro-channel.Therefore,furtherresearchisneededtooptimizethemanufacturingtechniqueandtheformulationofthePCMmicrocapsulestoimprovetheirdispersionandstabilityintheworkingfluid.

AnotherchallengeisthelimitedheatcapacityofPCMmicrocapsulesuspensioncomparedtoconventionalheattransferfluids.WhilePCMmicrocapsulesuspensioncanofferefficientthermalenergystorageandreleaseduringphasechange,theyhavealoweroverallheatcapacitythanconventionalheattransferfluids.Thiscouldlimittheirapplicationincertainheattransferscenarioswhereahighheattransferrateoralargeamountofheattransferisrequired.

Inconclusion,thisstudydemonstratesthepotentialofutilizingPCMmicrocapsulesuspensioninmicro-channelsforheattransferenhancementandthermalenergystorage.Thefindingsprovidevaluableinsightsintotheheattransfermechanismandflowbehaviorofthissystem,whichcanguidethedesignandoptimizationofmicro-channelheatexchangersusingPCMmicrocapsules.However,furtherresearchisneededtoovercomethechallengesandlimitationsassociatedwithutilizingPCMmicrocapsulesuspensionandtoexploretheirpotentialapplicationsindifferentheattransferscenarios.Inaddition,theuseofPCMmicrocapsulesinheatexchangersalsobringssomechallengesandlimitations.Oneofthemajorchallengesisthedifficultyincontrollingthesize,shape,anddistributionofthemicrocapsules,whichcanaffecttheirthermalperformanceandstability.Moreover,thestabilityanddurabilityofthemicrocapsulesunderrepeatedthermalcyclingandmechanicalstressrequirefurtherinvestigation.Furthermore,theoptimizationofthemicroencapsulationprocessandthechoiceofsuitablePCMmaterialsarealsocriticaltoachievehighthermalenergystorageandreleaseefficiency.

AnotherpotentiallimitationofthePCMmicrocapsulesuspensionistheriskofcloggingorfoulingofthemicro-channels,especiallywhensmall-sizedmicrocapsulesareused.Thiscanreducetheheattransferperformanceandincreasetheflowresistance,leadingtoenergylossandsystemfailure.Therefore,thedevelopmentofeffectivecleaningandmaintenancemethodsandtheevaluationofthelong-termperformanceandreliabilityofthePCMmicrocapsule-basedheatexchangersareessentialforpracticalapplications.

Nevertheless,despitethechallengesandlimitations,thePCMmicrocapsulesuspensionhasshownpromisingpotentialinvariousheattransferapplications,suchasthermalmanagementofelectronics,solarenergystorage,andwasteheatrecovery.Itcanalsobecombinedwithotherheattransferenhancementtechniques,suchassurfacemodificationandflowcontrol,tofurtherimprovetheoverallperformanceofthesystem.

Inconclusion,theuseofPCMmicrocapsulesinmicro-channelheatexchangersisapromisingapproachforenhancingheattransferperformanceandachievingthermalenergystorage.Theexperimentalandnumericalstudieshaveprovidedvaluableinsightsintotheheattransfermechanismandflowbehaviorofthissystem,whichcanguidethedesignandoptimizationofthemicro-channelheatexchangersusingPCMmicrocapsules.However,furtherresearchisneededtoovercomethechallengesandlimitationsassociatedwiththisapproachandtoexploreitspotentialapplicationsindifferentheattransferscenarios.OneareathatrequiresfurtherinvestigationisthestabilityofthePCMmicrocapsulesinlong-termoperation.Thedurabilityofthemicrocapsulesiscriticalforthepracticalimplementationoftheheatexchangers,astheleakageordegradationofthePCMmaterialcancompromisetheperformanceandreliabilityofthesystem.Severalstudieshavedemonstratedthevulnerabilityofthemicrocapsulestochemicalandmechanicalstresses,suchasoxidation,abrasion,anddeformation,whichcanalterthethermalpropertiesandphase-changebehaviorofthePCM.Hence,itisessentialtodevelopmorerobustencapsulationmethodsandmaterialsthatcanwithstandharshoperatingconditionsandextendthelifespanofthemicrocapsules.

Anotherchallengethatneedstobeaddressedisthescalabilityofthemicro-channelPCMheatexchangers.Whilethemicro-scaledesignallowsforhighheattransferratesandcompactsize,italsoposessignificantmanufacturingandassemblydifficulties,particularlywhendealingwithlarge-scalesystems.Theuseofmicrofabricationtechniques,suchaslasercutting,micro-injectionmolding,andmicro-3Dprinting,canhelptoovercomesomeofthescalabilityissues,buttheyalsorequirespecializedequipmentandexpertise.Therefore,developingcost-effectiveandscalablemanufacturingmethodsforthemicro-channelPCMheatexchangersiscrucialtoenabletheircommercialviabilityandwidespreadadoption.

Besides,thereisaneedtoexploretheintegrationofthemicro-channelPCMheatexchangersintovariousthermalmanagementsystemsandapplications.Thecurrentstudieshavemostlyfocusedonthecoolingandheatingofelectronicdevicesandbuildings,butthereareotherpotentialfieldswherethePCM-basedheatexchangerscanprovidesignificantadvantages.Forinstance,theycanbeusedinthesolarenergysystemtostoreandreleasethermalenergy,intheprocessindustrytoimproveheatrecoveryandenergyefficiency,andinthetransportationsectortoenhancethethermalmanagementofvehiclesandaircraft.Investigatingthefeasibilityandbenefitsoftheseapplicationscanexpandthescopeandimpactofthemicro-channelPCMheatexchangersandbringnewopportunitiesforinnovationanddevelopment.

Inconclusion,themicro-channelPCMheatexchangerisapromisingtechnologyforenhancingtheheattransferperformanceandachievingthermalenergystorageinvariousapplications.Theexperimentalandnumericalstudieshaveshedlightontheunderlyingphysicsandflowbehaviorofthissystem,butfurtherresearchisneededtoaddressthechallengesandlimitationsassociatedwithitsimplementationandexploreitspotentialindifferentfields.Withcontinuouseffortsandinnovations,themicro-channelPCMheatexchangercancontributetotheadvancementofenergyconservation,environmentalprotection,andsustainabledevelopment.Inadditiontoitsapplicationsinthermalmanagement,themicro-channelPCMheatexchangerhasalsobeeninvestigatedforotherareassuchasfoodpreservation,medicalcooling,andwasteheatrecovery.Inthefieldoffoodpreservation,PCM-basedpackaginghasbeenshowntoimprovetheshelflifeofperishableproductsbymaintainingaconstanttemperatureduringtransportationandstorage.TheuseofPCMinmedicalcoolingcanhelppreventhypothermiaduringsurgeryandreducetheriskoftissuedamageinorganpreservation.Thewasteheatrecoverypotentialofthemicro-channelPCMheatexchangercanbeutilizedinindustriessuchasautomotiveandpowergeneration,wheretherecoveryofwasteheatcanimproveefficiencyandreducegreenhousegasemissions.

However,theimplementationofmicro-channelPCMheatexchangertechnologyfacesseveralchallengesandlimitations.Oneofthemajorchallengesisthecostofproductionandscalingupthetechnologytomeetcommercialdemands.Theuseofexpensivematerialsforthemicro-channelfabricationandthecostofPCMencapsulationcanincreasethecostofproduction.Furthermore,theoptimizationoftheheatexchangerdesignandtheselectionofsuitablePCMarecriticalfactorsthatcanaffecttheperformanceandefficiencyofthesystem.

AnotherlimitationisthepotentialforPCMleakageormelting,whichcancausedamagetothesystemandtheenvironment.Properinsulation,PCMselection,andsystemmaintenancearenecessarytominimizetheriskofleakageandensuresafeoperation.Additionally,thethermalresistancecausedbyfluidflowandheattransferlimitationsinthemicro-channelscanaffecttheoverallheattransferperformanceofthesystem.Thetrade-offbetweenthepressuredropandheattransferratemustbecarefullyconsideredinthedesignandoperationofthemicro-channelPCMheatexchanger.

Despitethesechallengesandlimitations,themicro-channelPCMheatexchangerpresentsapromisingtechnologyforenergyconservation,environmentalprotection,andsustainabledevelopment.Ongoingresearchanddevelopmentcanaddressthecurrentlimitationsandexpandthepotentialapplicationsofthistechnology.Theintegrationofmicro-channelPCMheatexchangerswithotherrenewableenergysystems,suchassolarthermalandgeothermalsystems,canfurtherenhancetheirefficiencyandperformance.Thedevelopmentofcost-effectiveandenvironmentallyfriendlyPCMmaterialscanalsocontributetothecommercializationandwidespreadadoptionofthistechnology.Withtheincreasingdemandforenergy-efficientandsustainablethermalmanagementsystems,themicro-channelPCMheatexchangerispoisedtoplayasignificantroleinshapingthefutureofenergyutilizationandconservation.Inadditiontothepotentialadvantagesmentionedabove,micro-channelPCMheatexchangerscanalsoaddresscertainchallengesassociatedwithconventionalcoolingandheatingsystems.Forinstance,inairconditioningunits,conventionalrefrigerantsareknowntohavehighglobalwarmingpotential(GWP),andtheirusecancontributetothedepletionoftheozonelayer.Micro-channelPCMheatexchangers,ontheotherhand,canusenon-hazardousandnon-toxicmaterialsasphasechangemedia,makingthemasaferandmoreeco-friendl