Numerical-simulation-study-on-discharging-process-

Numericalsimulationstudyondischargingprocessofthedirect-contactphasechangeenergystoragesystemWeilongWanga,HailongLib,ShaopengGuoc,ShiquanHed,⇑,JingDinga,JinyueYanb,e,⇑,JianpingYangfaSchoolofEngineering,SunYat-senUniversity,Guangzhou,ChinabSchoolofBusiness,SocietyandEnergy,MälardalenUniversity,Västerås,SwedencSchoolofEnergyandEnvironment,InnerMongoliaUniversityofScienceandTechnology,Baotou,ChinadAcademyofBuildingEnergyEfficiencyofGuangzhouUniversity,Guangzhou,ChinaeEnergyProcessDivision,RoyalInstituteofTechnology,Stockholm,SwedenfSchoolofChemistryandChemicalEngineering,SouthChinaUniversityofTechnology,Guangzhou,ChinahighlightsDischargingprocessofthedirect-contactTEScontainerarestudiedexperimentally.Direct-contactsolidificationprocessaremodeledandsimulatedbyCFD.EffectsofHTOflowrateandinlettemperatureonsolidificationrateofPCMareclarified.articleinfoArticlehistory:Received4August2014Receivedinrevisedform4March2015Accepted22March2015Availableonline18April2015Keywords:MobilizedthermalenergystoragesystemPhasechangematerialsComputationalfluiddynamicsSolidificationabstractThemobilizedthermalenergystoragesystem(M-TES)hasbeendemonstratedasapromisingtechnologytosupplyheatusingwasteheatinindustriestodistributedusers,whereheatdischargingdetermineswhetherM-TESsystemcansatisfytherequiredheatingrate.Theobjectiveofthisworkistoinvestigatethesolidificationmechanismofphasechangematerials(PCM)forheatdischarginginadirect-contactthermalenergystorage(TES)containerforM-TES.A2-dimensional(2D)numericalsimulationmodeloftheTEStankisdevelopedinANSYSFLUENT,andvalidatedwiththeexperimentalmeasurement.Effectsofflowrateandinlettemperatureofheattransferoil(HTO)werestudied.Resultsshowthat(a)thedischargingprocessincludestheformationofsolidifiedPCMfollowedbythesinkingofsolidifiedPCM;(b)thedischargingtimeofM-TEScanbereducedbyincreasingtheflowrateofheattransferoil.Whentheflowrateisincreasedfrom0.46m3/hto0.92m3/h,thesolidifiedPCMisincreasedfrom25vol.%to90vol.%within30min;(c)thedischargingtimecanbereducedbydecreasingtheinlettem-peratureofHTO.Whiletheinlettemperatureisreducedfrom50Cto30C,thesolidifiedPCMisincreasedfrom60vol.%to90vol.%within30min.ThisworkprovidesengineeringinsightsfortherationaldesignofdischargingprocessforM-TESsystem.2015ElsevierLtd.Allrightsreserved.1.IntroductionEnormousamountoflow-temperatureheatproducedinindus-trialprocessisrejectedtoambientsurroundingdirectlywithoutfurtherusage[1].Thedistrictheating(DH)networkprovidesaviablepathtodeliversuchkindofexcessheattocoverdailyheatconsumptioninresidentialsectors[2–4].However,buildingaDHisnotalwayscost-efficientduetotremendousinvestmentsonpipelineconstruction,especiallywhenthelocalheatdemandissmall[5,6].Asanalternative,mobilizedthermalenergystorage(M-TES)system,supplyingheatbythermalenergystorage(TES)containerinatruck,hasbeenproposedasanewenergytrans-portationsystem,inwhichhighenergy–densityTEStechnologyisthekeyfactorforsystem’senergy-utilizationefficiency[7–9].TwokindsofM-TESsystemusingadirect-/indirect-contactTEScontainerhavebeenbuiltinYan’slaboratorytotesttheirenergytransferandstorageperformance[10–13].Tillnow,forindirect-contactTEScontainerinM-TESsystem,studieshavebeencarriedoutondevelopingeffectiveTESmaterials,aswellasenhancedheattransferfromtheaspectsofbothTEScontainer2015ElsevierLtd.Allrightsreserved.⇑Correspondingauthorsat:SchoolofBusiness,SocietyandEnergy,MälardalenUniversity,Västerås,Sweden(J.Yan),AcademyofBuildingEnergyEfficiencyofGuangzhouUniversity,Guangzhou,China(S.He).E-mailaddresses:[e-mail](S.He),[e-mail](J.Yan).AppliedEnergy150(2015)61–68ContentslistsavailableatScienceDirectAppliedEnergyjournalhomepage:ficiencywithlargerenergystoragecapacityandshortercharginganddischargingtimeneeded.InYan’slatestwork,thechargingprocesshasbeensimulatedtounderstandthemeltingbehaviorofphasechangematerial(PCM)andheatandmasstransfermechanisminthedirect-contactTEScontainer[14].Incontrast,dischargingprocessofdirect-contactTESsystemhasnotbeenfullyunderstood,whichisessentialfortheoptimizationoftheM-TESsystem.However,toourbestknowl-edge,duetoitscomplicatedmassandheattransferprocess[15],fewexperimentalandsimulationworkshavebeencarriedoutonthedirect-contactdischargingprocess.Herein,thesolidificationmechanismofPCMforheatdischarg-inginadirect-contactcontainerforM-TEShasbeenstudiedinthiswork.A2-dimensionalnumericalsimulationmodelforthedis-chargingprocessofthedirect-contactTESsystemisdevelopedinANSYSFLUENT,andverifiedbytheexperimentaldata.Withtheverifiedmodel,theeffectsoftheheattransferoil(HTO)flowrateandinlettemperatureonthedischargingtimeandphasechangebehaviorofthePCMareinvestigated.Theresultsprovideinsightsandguidelinesfortherationaldesignandoptimizationofthedirect-contactM-TESsystem.2.ExperimentsLab-scaleM-TESsystemwiththedirect-contactTEScontainerwasconstructedinthelab,asshowninFig.1.Thedirect-contactcontaineriscomposedofacyli