过冷沸腾热传递不规则模型分析(分析中)VIP专享VIP免费

AfractalanalysisofsubcooledflowboilingheattransferBoqiXiaoa,b,BomingYua,*aDepartmentofPhysics,HuazhongUniversityofScienceandTechnology,1037LuoyuRoad,Wuhan430074,Hubei,PRChinabDepartmentofPhysicsandElectromechanicalEngineering,SanmingUniversity,25JingdongRoad,Sanming365004,Fujian,PRChinaReceived18July2006;receivedinrevisedform8April2007AbstractAfractalmodelforthesubcooledflowboilingheattransferisproposedinthispaper.Theanalyticalexpressionsforthesubcooledflowboilingheattransferarederivedbasedonthefractaldistributionofnucleationsitesonboilingsurfaces.Theproposedfractalmodelforthesubcooledflowboilingheattransferisfoundtobeafunctionofwallsuperheat,liquidsubcooling,bulkvelocityoffluid(orReynoldsnumber),fractaldimension,theminimumandmaximumactivecavitysize,thecontactangleandphysicalpropertiesoffluid.Noadditional/newempiricalconstantisintroduced,andtheproposedmodelcontainslessempiricalconstantsthantheconventionalmodels.Theproposedmodeltakesintoaccountallthepos-siblemechanismsforsubcooledflowboilingheattransfer.Themodelpredictionsarecomparedwiththeexistingexperi-mentaldata,andfairagreementbetweenthemodelpredictionsandexperimentaldataisfoundfordifferentbulkflowrates.�2007ElsevierLtd.Allrightsreserved.Keywords:Subcooledflowboiling;Fractal;Heattransfer1.IntroductionThesubcooledflowboilingiswidelyappliedinengineeringandtechnology.Inthedevelopmentofmoderncoolingsystemssuchasinternalcombustionengines,powerengineering,nuclearreactorsandmicroproces-sors,theincreasingoutputofspecificpowercombinedwithamostcompactspaceandweightsavingdesignleadstohighthermalloadsonheatingsurfaces.Forsuchdevices,ahighcoolantpoweristoberequiredwithlimitationsontheavailablesurfaceareaandthemassfluxofliquidcoolantaswellastheacceptablewalltem-perature,andacontrolledoperatingmodetotheboilingregimeisdesirable.Insubcooledflowboilingheattransferitisgenerallyrecognizedthattherearethreemainmechanismscon-tributingtothewallheatflux(qW):single-phaseheattransfer(qsp),micro-layerevaporation(qev),andthe0301-9322/$-seefrontmatter�2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.ijmultiphaseflow.2007.05.001*Correspondingauthor.E-mailaddress:yuboming2003@yahoo.com.cn(B.Yu).InternationalJournalofMultiphaseFlow33(2007)1126–1139www.elsevier.com/locate/ijmulflow过冷沸腾热传递的不规则分析本文提到的过冷沸腾传热是不规则模型，过冷沸腾传热模型的分析表达式是基于沸腾表面得成核集不规则分配而衍生的本文所推荐的过冷沸腾传热不规则模型是由壁面过热，过冷流体，流体体积速率或雷诺数，不规则容积最小及最大主动腔尺寸，接触角和流体物理特性而得出的方程。没有介绍附加的或新的经验常数，而且所推荐模型包含的经验常数比传统模型有的少.推荐模型解释了过冷沸腾传热的所有可能机理.模型的判断与已存在的经验数据比较,及二者间的清晰的一致性，从而发现不同体积流体率.过冷沸腾广泛的应用到工程技术领域,在现代冷却系统的发展中,如内燃机,发动机,核反应堆与微处理,结合极多的紧凑表面及节省重量的设计的越来越多的输出具体功率导致高热量加载于供热表面。对于这个设备,对于有效表面区域的局限性，高？功率是必需的.并且液体流量团也是可接受的壁温度,所以一个受约束的沸腾体系操作模型是值得的.在过冷沸腾传热普遍公认对于壁热流量有三个主要的机理因素:单相传热,微观层蒸发,流体的敏感热度(依靠气泡脱离的体积排空).sensibleheatoffluidthatoccupiesthevolumeevacuatedbyadepartingbubble(qb).ThusthewallheatfluxcanbeexpressedasqW¼qspþqevþqbð1ÞBowring(1962)obtainedtherelationbetweenqevandqbase¼qb=qevð2ÞTheevapo...