熱對流及對流換熱Heatconvectionandconvectiveheattransfer《儲能技術概論》《EnergyStorageTechnology》主講教師：Instructor:

CONTENTS熱對流heatconvection01PART對流換熱Convectiveheattransfer02PART目錄熱對流及對流換熱的應用Applicationsofthermalconvectionandconvectiveheattransfer03PART熱對流heatconvectionPART01一、熱對流heatconvection熱對流Heatconvection又稱對流傳熱，是指流體（氣體和液體）其質(zhì)點發(fā)生相對位移而引起的熱量傳遞過程。alsoknownasconvectionheattransfer,referstotheheattransferprocesscausedbytherelativedisplacementofparticlesinafluid(gasandliquid).熱對流的原理Theprincipleofthermalconvection當流體被加熱時，其溫度升高，分子動能增加，分子運動加劇，導致流體體積膨脹，密度減小。由于密度差異，熱流體上升，而冷流體下沉，形成對流環(huán)流。Whenthefluidisheated,itstemperaturerises,themolecularkineticenergyincreases,andthemolecularmotionintensifies,resultingintheexpansionofthefluidvolumeandthedecreaseofdensity.Duetothedifferenceindensity,thehotfluidriseswhilethecoldfluidsinks,formingaconvectivecirculation.熱對流的發(fā)生依賴于流體的宏觀運動，可以由流體的內(nèi)部溫度差異引起，也可以由外部力量驅(qū)動。Theoccurrenceofthermalconvectiondependsonthemacroscopicmotionofthefluid,whichcanbecausedbyinternaltemperaturedifferencesinthefluidordrivenbyexternalforces.一、熱對流heatconvection熱對流可以根據(jù)不同的標準進行分類，其中最常見的分類方式是按流動介質(zhì)和發(fā)生原因進行分類。Thermalconvectioncanbeclassifiedaccordingtodifferentcriteria,amongwhichthemostcommonclassificationisbasedontheflowmediumandthecauseofoccurrence.一、熱對流heatconvection按流動介質(zhì)分類可以分為氣體對流和液體對流Accordingtotheclassificationofflowmedium,itcanbedividedintogasconvectionandliquidconvection氣體對流Gasconvection現(xiàn)象較為明顯，因為氣體的分子間距離較大，分子運動較為自由，容易形成對流。例如，房間內(nèi)加熱器加熱空氣，熱空氣上升，冷空氣下沉，形成自然對流。Thephenomenonismoreobvious,becausethedistancebetweengasmoleculesislarge,andthemovementofmoleculesisfree,soitiseasytoformconvection.Forexample,whenaheaterheatstheairinaroom,thehotairrisesandthecoldairsinks,formingnaturalconvection.01液體對流Liquidconvection雖然不如氣體對流明顯，但在某些情況下也非常重要。例如，在鍋爐和熱水器中，水被加熱后上升，冷水下沉，形成對流環(huán)流，使水溫均勻。Althoughlessobviousthangasconvection,itisalsoimportantinsomecases.Forexample,inboilersandwaterheaters,waterrisesafterbeingheated,whilecoldwatersinks,formingacirculatingconvectionthatmakesthewatertemperatureuniform.02一、熱對流heatconvection按發(fā)生原因分類可以分為自然對流和強制對流Accordingtothecauseofoccurrence,itcanbeclassifiedintonaturalconvectionandforcedconvection自然對流NaturalConvection由于流體內(nèi)部溫度差異引起的密度差異所導致的流體流動。這種流動不需要外部力量的驅(qū)動，完全由流體自身的性質(zhì)決定。自然對流的流速一般較低，換熱強度相對較低。例如，煮水時水的上下循環(huán)流動就是自然對流的一種表現(xiàn)。Afluidmovementdrivenbydensitydifferencescausedbytemperaturevariationswithinthefluid.Thisflowoccurswithoutexternalforceapplication,entirelydeterminedbythefluidsinherentproperties.Naturalconvectiontypicallyfeatureslowerflowvelocitiesandrelativelyweakerheattransferintensity.Aclassicexampleistheupwardanddownwardcirculationofwaterduringboiling,whichexemplifiesthisphenomenon.01一、熱對流heatconvection按發(fā)生原因分類可以分為自然對流和強制對流Accordingtothecauseofoccurrence,itcanbeclassifiedintonaturalconvectionandforcedconvection強制對流Forcedconvection由于外部力量推動流體運動所形成的對流。這種對流方式可以人為地控制流速和流動方向，因此換熱強度較高。例如，空調(diào)系統(tǒng)通過風扇強制氣流流動，實現(xiàn)室內(nèi)空氣的對流。Theconvectionformedbytheexternalforcetopromotethemovementoffluid.Thistypeofconvectioncanbeartificiallycontrolledintheflowrateanddirection,sotheheattransferintensityishigher.Forexample,theairconditioningsystemusesfanstoforcetheairflowtoachievetheconvectionofindoorair.02對流換熱ConvectiveheattransferPART02二、對流換熱Convectiveheattransfer對流換熱Convectiveheattransfer流體流經(jīng)固體表面時，流體與固體表面之間的熱量傳遞過程。theheattransferprocessbetweenafluidandasolidsurfaceasthefluidflowsthroughthesolidsurface.這一過程既包括流體分子間的熱傳導，也包括流體的宏觀位移所帶來的熱量傳遞。Thisprocessincludesboththeheatconductionbetweenfluidmoleculesandtheheattransfercausedbythemacroscopicdisplacementoffluid.對流換熱的原理Theprincipleofconvectionheattransfer單位時間內(nèi)通過單位面積的熱量與固體表面和流體之間的溫度差成正比，與對流換熱系數(shù)成正比。theheatpassingthroughaunitareaperunittimeisproportionaltothetemperaturedifferencebetweenthesolidsurfaceandthefluid,andproportionaltotheconvectiveheattransfercoefficient.二、對流換熱Convectiveheattransfer對流換熱Convectiveheattransfer流體流經(jīng)固體表面時，流體與固體表面之間的熱量傳遞過程。theheattransferprocessbetweenafluidandasolidsurfaceasthefluidflowsthroughthesolidsurface.這一過程既包括流體分子間的熱傳導，也包括流體的宏觀位移所帶來的熱量傳遞。Thisprocessincludesboththeheatconductionbetweenfluidmoleculesandtheheattransfercausedbythemacroscopicdisplacementoffluid.對流換熱系數(shù)受到流體性質(zhì)、流速、固體表面形狀和尺寸等多種因素的影響。Theconvectiveheattransfercoefficientisaffectedbyfluidproperties,flowvelocity,solidsurfaceshapeandsize.二、對流換熱Convectiveheattransfer對流換熱可以根據(jù)不同的標準進行分類，其中最常見的分類方式是按流動狀態(tài)和發(fā)生原因進行分類。Convectiveheattransfercanbeclassifiedaccordingtodifferentcriteria,amongwhichthemostcommonclassificationisaccordingtoflowstateandcause.二、對流換熱Convectiveheattransfer按流動狀態(tài)分類可以層流對流換熱和湍流對流換熱Accordingtothestateofflow,itcanbeclassifiedaslaminarconvectionheattransferandturbulentconvectionheattransfer層流對流換熱Laminarflowconvectionheattransfer在層流狀態(tài)下，流體質(zhì)點沿平行方向分層流動，層間無宏觀混合。此時熱量主要靠熱傳導傳遞，對流換熱較弱。Inlaminarflowstate,thefluidparticlesflowinparalleldirectionwithoutmacroscopicmixingbetweenlayers.Atthistime,heatismainlytransferredbyheatconduction,andtheconvectiveheattransferisweak.01湍流對流換熱Turbulentconvectionheattransfer在湍流狀態(tài)下，流體質(zhì)點劇烈混合，有強烈的橫向脈動。此時對流換熱效率遠高于層流對流換熱效率。Intheturbulentstate,thefluidparticlesareviolentlymixedandthereisastronglateralpulsation.Atthistime,theconvectiveheattransferefficiencyismuchhigherthanthatoflaminarflow.02二、對流換熱Convectiveheattransfer按發(fā)生原因分類分為自然對流換熱和強制對流化熱Accordingtothecauseofoccurrence,itcanbeclassifiedintonaturalconvectionheattransferandforcedconvectionheattransfer自然對流換熱Naturalconvectionheattransfer由于流體內(nèi)部溫度差異引起的密度差異所導致的流體流動，進而形成的對流換熱。theflowoffluidcausedbythedensitydifferencecausedbythetemperaturedifferenceinsidethefluid,andthentheconvectionheattransferisformed.01強制對流換熱Forcedconvectionheattransfer由于外部力量（如泵、風扇等）推動流體運動所形成的對流換熱。theconvectionheattransferformedbyexternalforces(suchaspumps,fans,etc.)topromotefluidmotion.02二、對流換熱Convectiveheattransfer對流換熱的影響因素Factorsaffectingconvectionheattransfer01.流體性質(zhì)Fluidproperties導熱系數(shù)大的流體，分子熱運動傳遞熱量的能力強，有利于對流換熱。比熱容大的流體，吸收或放出相同熱量時溫度變化小，能攜帶更多熱量，對流換熱效果好。密度大的流體，單位體積質(zhì)量大，攜帶熱量多，對對流換熱有促進作用。粘度大的流體，流動阻力大，流速低，不利于對流換熱。Fluidswithhighthermalconductivitydemonstratesuperiorheattransferefficiencythroughmolecularmotion,enhancingconvectiveheatexchange.Thosewithhigherspecificheatcapacityexhibitminimaltemperaturefluctuationswhenabsorbingorreleasingequivalentheat,allowingthemtocarrymorethermalenergyandimproveconvectiveperformance.High-densityfluids,characterizedbygreaterunitmasscapacity,effectivelytransportmoreheatandfacilitatebetterconvection.Conversely,viscousfluidsgeneratesignificantflowresistanceandlowflowvelocities,whichhindereffectiveheattransferthroughconvection.二、對流換熱Convectiveheattransfer對流換熱的影響因素Factorsaffectingconvectionheattransfer02.流速Flowrate流速越大，流體與固體表面之間的熱量交換越迅速，對流換熱強度越高。然而，流速過大也會導致流動阻力增加和能量損失增大。thegreatertheflowrate,thefastertheheatexchangebetweenthefluidandthesolidsurface,andthehighertheintensityofconvectionheattransfer.However,toolargeaflowratewillalsoleadtoincreasedflowresistanceandenergyloss.二、對流換熱Convectiveheattransfer對流換熱的影響因素Factorsaffectingconvectionheattransfer03.固體表面形狀和尺寸Surfaceshapeanddimensionsofsolids不同形狀的表面會影響流體的流動和換熱。例如，肋片管通過增加表面積來強化換熱。固體表面的粗糙度也會影響對流換熱效果。粗糙度大的表面會使流體流動紊亂，增加流體與表面的接觸面積，從而增強對流換熱。Differentsurfaceconfigurationssignificantlyinfluencefluidflowandheattransfer.Forexample,finnedtubesenhanceheatexchangebyincreasingthesurfacearea.Theroughnessofsolidsurfacesalsoimpactsconvectiveheattransferefficiency.Roughersurfacesinduceturbulentflowpatterns,whichincreasesthecontactareabetweenthefluidandthesurface,therebyboostingconvectiveheattransfer.二、對流換熱Convectiveheattransfer對流換熱的影響因素Factorsaffectingconvectionheattransfer04.溫度差Temperaturedifference溫差越大，單位時間內(nèi)傳遞的熱量越多，對流換熱強度越大。thegreaterthetemperaturedifference,themoreheatistransferredperunittime,andthestrongertheconvectiveheattransferintensity.熱對流及對流換熱的應用ApplicationsofthermalconvectionandconvectiveheattransferPART03三、熱對流及對流換熱的應用Applicationsofthermalconvectionandconvectiveheattransfer（一）應用于熱儲能系統(tǒng)Appliedtothethermalenergystoragesystem熱量通過熱對流傳遞到儲能介質(zhì)中，實現(xiàn)能量的儲存。當需要釋放能量時，儲能介質(zhì)中的熱量再通過熱對流傳遞到工作介質(zhì)中，實現(xiàn)能量的釋放。Theheatistransferredtotheenergystoragemediumthroughheatconvectiontorealizeenergystorage.Whentheenergyneedstobereleased,theheatintheenergystoragemediumistransferredtotheworkingmediumthroughheatconvectiontorealizeenergyrelease.三、熱對流及對流換熱的應用Applicationsofthermalconvectionandconvectiveheattransfer（二）應用于電池熱管理Appliedtobatterythermalmanagement設計合理的散熱結(jié)構(gòu)和流動通道，可以利用熱對流將電池產(chǎn)生的熱量及時散發(fā)出去，保持電池在適宜的溫度范圍內(nèi)運行。thereasonableheatdissipationstructureandflowchannelcanbedesignedtousetheheatconvectiontodissipatetheheatgeneratedbythebatteryintime,soastokeepthebatteryrunningintheappropriatetemperaturerange.（三）應用于微電網(wǎng)能量管理Appliedtoenergymanagementofmicrogrid在微電網(wǎng)中，儲能裝置起著平衡供需、提高供電可靠性和穩(wěn)定性的重要作用。Inmicrogrid,energystoragedeviceplaysanimportant