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InternationalJournalofThermalSciences45(2006)269–283www.elsevier.com/locate/ijtsAstudyoflocalheattransfermechanismsalongtheentireboilingcurvebymeansofmicrosensorsM.Buchholza,H.Aurachera,∗,T.Lüttichb,W.MarquardtbaInstitutfürEnergietechnik,TechnischeUniversitätBerlin,Marchstr.18,KT1,D-10587Berlin,GermanybLehrstuhlfürProzesstechnik,RWTHAachen,Turmstr.43,D-52064Aachen,GermanyReceived22December2003;receivedinrevisedform24August2004;accepted24August2004Availableonline12October2005AbstractAnarrayof36microthermocouples(38µmdiameter)embeddedinahorizontalcopperheater(distancetothesurface3.6µm),amicroopticalprobe(tipdiameter∼1.5µm)andamicrothermocoupleprobe(tipdiameter∼16µm),bothmoveableabovetheheatersurface,areappliedtostudyheattransfermechanismsalongtheentireboilingcurveundersteady-stateconditions.TestﬂuidsareisopropanolandFC-3284.Innucleateboiling,verylocalizedandrapidtemperaturedropsareobservedindicatinghighheatﬂuxesatthebottomofthebubbles.AlreadybeforereachingCHF,hotspotsoccurthesizeofwhichincreasestowardstheLeidenfrostpoint.Intheentiretransitionboilingregimewettingeventsareobserved,butnoonesinﬁlmboiling.Inlowheatﬂuxnucleateboilingsmallvaporsuperheatsexistinthebubblesandstrongsuperheatsinthesurroundingliquid.Thischaracteristicchangescontinuouslywithincreasingwallsuperheat:theliquidsurroundingthevaporapproachessaturationwhereasthevaporbecomesmoreandmoresuperheated.Inﬁlmboilingthebubblesleavingthevaporﬁlmcanreachsuperheatsof40Knearthesurface.Theopticalprobesconﬁrmaliquidrichlayernearthesurfacebetweennucleateboilingandhighheatﬂuxtransitionboiling.Thevoidfractioninthislayerincreasescontinuouslywiththedistancetothesurfaceuntilamaximumvaluewhichseemstobelinkedtothebubbledeparturediameter.2005ElsevierSAS.Allrightsreserved.Keywords:Microthermocouple;Opticalprobe;Microthermocoupleprobe;Poolboiling;Transitionboiling;Surfacewetting;Drypatch;Surfacetemperature;Boilingmechanism;Voidfraction;Isopropanol;FC-3284;PF-5052;Temperatureﬁeld;Temperaturecontrol;Tw