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IranC2112012ElsevierLtd.Allrightsreserved.applyingandlesssusceptibletobrakefade,whichlargelycontributedtotheirpopularity1.Thethermalanalysisofbrakediscsisaprimarystageinthestudyofthebrakesystemsbecausethetemperaturedeterminesthermomechanicalbehaviorofthestructure.Inthebrakingsurface,hightemperaturesandthermalgradientsareproduced.Thisgeneratesstressanddeformationsinxstructureofeinthelocalheattransfercoefficientdistribution.Therefore,assumingaconstantvalueforheattransfercoefficientdoesnotseemtobelogical.Inthispaper,thermalanalysisofthewheelmountedbrakediscR920KfortheER24PClocomotivewhichismanufacturedinMAPNALocomotiveEngineeringandManufacturingCompanyMLCincooperationwithSIEMENSAGisinvestigated.DrivingforceofER24PCLocoissuppliedusingadieselelectricenginewiththemaximumspeedof160km/h.Thislocomotiveisusedtopullthepassengerwagons.Forcalculatingtheheattransfercoefficient,Correspondingauthor.Tel.þ989197481360faxþ982188013029.ContentslistsavailableatAppliedThermalEngineering512013948e952EmailaddressBehnam.ghadimiut.ac.irB.Ghadimi.brakesinmanydifferenttypesofvehicles.Severaladvantagesofbrakediscsovershoesbrakesarereported,includingbetterstoppingperformancedisccooledreadily,easytocontrolnotselfcalculationsinbrakediscs5,12,13.Asitisreportedintheexperimentalresults,CompletheventilatedtypebrakedisccausesagreatchangAsthespeedrestrictionoftrainscontinuestoexpand,overheatingandthermaldeformationonbrakesystemsaregoingtobecriticalforemergencybraking.Evenifdynamicbrakingsystemsareusedinnormalservicebraking,theirperformancesarenotsufficienttoensureanemergencybrakingathighspeed.Sofrictionbrakingsystemshavecrucialroleinemergencybraking.Forseveralyears,brakediscsincreasinglybecamemorepopularthanshoestransferonthetotalamountofdissipatedenergytothesurroundisinsignificant3e7,andconductionandconvectionmodesofheattransferplayacrucialroleincontributionofheatexchangeofthebrakesystem.TheproblemofthefluidflowbetweenthefinsoftheventilatedtypeofbrakediscsisoftenanalyzedinindividualstudiesbasedontheCFDmethod8e11.Neverthelessoftenanaverage,constantvalueoftheheattransfercoefficientisusedattemperature1.Introductionwhichtheconsequencesaremanifestedbytheappearanceofcracks2.Duringthenormalbraking,influenceoftheradiationheatarticleinfoArticlehistoryReceived17September2012Accepted29October2012Availableonline7November2012KeywordsWheelmountedbrakediscPadHeattransferLocomotive13594311/eseefrontmatterC2112012ElsevierLtd.http//dx.doi.org/10.1016/j.applthermaleng.2012.10.05abstractInrecentdecadestheimprovementofthebrakingperformancesarerequiredduetohighspeedoftrains.Thegeneratedfrictionalheat,duringbrakingoperationcausesseveralnegativeeffectsonthebrakesystemsuchasbrakefade,prematurewear,thermalcracksanddiscthicknessvariation.Itisthenimportanttodeterminethetemperaturefieldofthebrakedisc.Inthepresentwork,thermalanalysisofthewheelmountedbrakediscR920KfortheER24PClocomotiveisinvestigated.Thebrakediscandfluidzonearesimulatedasa3Dmodelwithathermalcouplingboundarycondition.Thebrakingprocessissimulatedinlaboratoryandtheexperimentaldataareusedtoverifythesimulationresults.Duringthebraking,themaximumtemperaturewasobservedinthemiddleofbrakingprocessinsteadofthebrakingendpoint.Moreover,alargelaggingwasobservedforfinstemperaturewhichrendersnocoolingatthebeginningofthebraking.Discsurfacetemperaturesincreasedbrakingtime,andthendecreased.Laggingeffectrendersnocoolingatthebeginningofthebraking.withincreasingThermalanalysisoflocomotivewheelmountedB.Ghadimia,,F.Kowsarya,M.KhoramibaSchoolofMechanicalEngineering,CollegeofEngineering,UniversityofTehran,Tehran,bMechanicalEngineeringDepartment,MAPNALocomotiveCompany,Karaj,IranhighlightsAteachtimestepthelocalHTCwascalculated,andusedfordiscthermalNumericalresultscomparewellwithexperimentaldata.AppliedThermaljournalhomepagewww.elseviAllrightsreserved.1brakediscanalysis.SciVerseScienceDirectEngineeringer.com/locate/apthermengparts.IfthelocomotivestopscompletelyV2¼u2¼0thenalltherotatingpartswillbeexpressedrelativetotherevolutionsofthewheel.Eq.1canberewrittenasfollowsEb¼12m1þIR2wmV21¼12kcfmV212flywheelmassesandassemblyoflocowheel.lEngineering512013948e952949thefluidflowwithinthechannelwasmodeledusingtheFLUENTCFDsoftware.Ateachtimestep,duetothelocomotivespeedandtemperaturedistributioninthebrakedisc,thelocalheattransfercoefficientoffinswascalculatedandwasappliedasaboundaryconditionforthebrakediscthermalanalysis.Anexperimentaldataverifiedthemodelingresults.2.ExperimentalsetupArailwaybrakediscsystemistestedontheZFDynamometerFig.1intheFaiveleyTransportCompanyandresultswerereportedtoMLC14.ZFDynamometerisabletorunwithspecificmissionprofilesindryandwetconditions.Thedynamometerhasanelectricmotorof536kWanduptofourcoupleableflywheelmassestosimulatevariousweightsandloadsofvehicles.Themeasurementoftemperatureisaveryimportantstepinthetestprocedure.Forthispurpose,aKTypeThermocouplein1.5mmthicknesswasused.Formodelingthebrakingphenomena,locomotivewheelwasacceleratedwiththeconstantvalueof0.8m/s2andreachedtothedesiredvelocity,thenthebrakingstartedandcausedconstantdecelerationwiththerateof1.117m/s2.Duringthebraking,brakingsurfaceandfinswalltemperatureswererecordedandusedforvalidatingthenumericalresults.3.ModelingTheER24PClocomotiveconsistsoftwobogies.EachbogiehasfourwheelswithonesetofwheelmountedbrakediscswhichconsistsoftwobrakediscsarrangedonbothsidesofawheelandareboltedtogetherthroughthewheelwebFig.2.3.1.ThermalmodelingRegardingtotheuniformpressureortheconstantwearFig.1.ZFdynamometerwithcoupleableB.Ghadimietal./AppliedThermaboundaryconditionatthecontactsurface,twomethodsareavailableforcalculatingthebrakingheatgenerationrate.Uniformpressuredistributioninthecontactregionisoftenvalidwhenthepadisnew.Howeverafterbrakingforseveraltimes,assumptionofuniformwearismorepragmatic.Inthisstudy,thepadwasusedseveraltimesanduniformwearbetweenpadandbrakediscisstabilized,hencetheheatfluxisjustafunctionoftimeanditisindependenceofthespatialvariables5.ForavehiclewhichisdeceleratingonalevelsurfacefromahighervelocityV1toalowervelocityV2thebrakingenergyEbcanbewrittenasEb¼12mC16V21C0V22C17þ12IC16u21C0u22C171whereIisrelatedtothemassmomentofinertiaoftherotatingparts,mlocomotivemassanduistheangularvelocityofrotatingFig.2.aWheelmountedbrakedisc,bwheelmountedbrakediscR920K,set,mounted.wherelistheheatgenerationratio,q00dandq00paretheheatfluxabsorbedbythebrakedisc,andpad,rrepresentsdensity,Cisthespecificheat,kthethermalconductivityandtheindexdandpindicatediscandpad,respectively.UsingEq.4and5,theheatTable1BrakediscR920Kdata.Brakingmassperbrakedisckg5456.5Wheeldiameteroriginmm1100Brakediscouterdiametermm920Brakediscinnerdiametermm640Widthofringmm24Widthoffinsmm30Densityofbrakediscmaterialkg/m37246SpecificheatofbrakediscmaterialJ/kgK500ThermalconductivityofbrakediscmaterialW/mK58Densityofbrakepadkg/m32180SpecificheatofbrakepadJ/kgK1090ThermalconductivityofbrakepadW/mK1.67Averagefrictioncoefficientm0.32AmbienttemperatureC14C55StarttemperatureofbrakediscC14C55Decelerationofvehicleaveragem/s21.177Engineering512013948e952B.Ghadimietal./AppliedThermal950wherekcfisthecorrectionfactorforrotatingmassesandRwisthewheelradius.BrakingpowerPbisequaltobrakingenergydividedbythebrakingtimet,orPb¼dEbdt3Forconstantdeceleration,Eq.2andEq.3yieldthebrakepowerasPb¼kcfmaðV1C0atÞ4whereaisthedecelerationofthelocomotive.Thedistributionofbrakingenergybetweenpadanddisccannotbepredictedreadily.Generally,thermalconductivityofthebrakepadsissmallerthanthedisckpkd,soonecanconsiderthatthetotalamountofthebrakingheatwillbecompletelyabsorbedbythebrakedisc.Thisassumptionleadstohighertemperatureestimationforbrakedisc.Toavoidthisissue,supposethatthebrakingoperationtimeisshort,hencethepadandbrakecanbeconsideredassemiinfinitesolidsandtheheatgenerationratiocanbecalculatedasfollows15l¼q00dq00p¼rdCdkdrpCpkp125Fig.3.Meshconstruction,abrakedisc,bfluidregion.fluxonthebrakingsurfacecanbefoundq00d¼lAðlþ1ÞkcfmaðV1C0atÞ6whereAisthediscandpadcontactarea.3.2.ModelingandboundaryconditionsForFEMandCFDanalysis,threedimensional3DconstructionsofbrakediscandcoolingairdomainweremodeledFig.3.Forsolvingthecontinuity,momentumandenergyequations,FLUENTunsteadysolverwasusedwithSIMPLEalgorithmforpressureandvelocitycouplingandkC0εrealizablemodelforviscousflowmodeling.PhysicalpropertiesofbrakediscandboundaryconditionsforanalysisaregiveninTable1.HeatfluxinthebrakingsurfaceiscalculatedfromEq.6.Ateachtimestep,accordingtothelocomotivespeedanddistributionoftemperatureinthebrakedisc,theFig.4.ThermalsimulationofbrakediscR920K,onestopsfrom154km/h.lEngineering512013948e952951B.Ghadimietal./AppliedThermalocalheattransfercoefficientoffinsiscalculatedbysolvingtheRANSandEnergyequationsinthefluidzone,andusedasaboundaryconditionforthebrakediscthermalanalysis.Thentheenergyequationwassolvedinthebrakediscandtemperaturedistributionatthesubsequenttimestepwascalculated.Thisprocedurecontinuesuntilthelocomotivecametoastop.4.ResultsanddiscussionThethermalanalysisofwheelmountedbrakediscofMAPNALocoER24PCwasconducted,inthecaseofoneemergencystopfrom154km/h.Fig.4showsnumericalresultsingoodcomparisonwithexperimentaldata.Fromthisfigure,itisseenthatthediscsurfacetemperaturewillincreasewithincreasingbrakingtimeandthenitdecreasesduetoasignificantreductioninheatgenerationvalueoverthebrakesurface.Duetotheheatconductioneffects,itispossibletoseealargedelayortimelaginfinstemperature.Thislaggingeffectrendersnocoolingatthebeginningofthebraking,sothesurfacetemperaturewillincreasesharply.Afterafewseconds,theheatfluxaffectsthefinsandfinstemperatureincreases.Byconvectioncoolingofthefins,brakingheatdissipatestotheair,andtherateofincreasinginsurfacetemperaturewillbereduced.TemperaturedistributiononthebrakediscinthreedifferenttimesispresentedinFig.5.Duetononuniformcoolingofthefinsintheirlength,themaximumtemperaturewasobservedinthedifferentregionsinthedifferenttimes.FromFig.5itisobviousthatthetemperaturevalueatthetopofthefinsisgreaterthanthetemperaturevaluebetweenthefins.Toelaboratethisbehavior,thedistributionofvelocityvectoratt¼20.5sispresentedinFig.6.LinearandrotationalvelocityeffectsFig.5.Temperaturedistributionsoftheontheairflowthroughthediscareclearlyvisibleinthisfigure.Stagnationandwakeregionregionaatthetopofthefins,andhighairvelocityabout22m/scanbeseenbetweenthefinsregionb.Stagnationregioncausedlowlocalheattransfercoefficientatregiona,whichleadstoareductioninheattransferanditcausesahighertemperaturevalue.Additionally,higherairvelocitybetweenthefinsleadstohighheattransfercoefficientbrakediscatdifferenttimes.Fig.6.Velocityvectordistributionatt¼20.5s.
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