工程传热学双语-四川大学chapter1-Introduction

工程传热学工程传热学（（EngineeringHeatTransferEngineeringHeatTransfer））SchoolofChemicalEngineeringDr.WenyunWEI•《传热学》杨世铭，陶文铨，第二版•《传热学》戴锅生，第二版•《HeatTransfer》(2ndEdition),byAnthonyF.Mills•《FundamentalsofHeatandMassTransfer》F.P.Incropera,D.P.DeWitt•《对流换热》V.S.阿巴兹•《凝结和沸腾》施明恒等编著•《数值传热学》陶文铨编著ReferenceCharacteristicsofthiscourse•Coveringavarietyofengineeringapplication,EngineeringHeatTransfer•Fundamentalcourse，introductioncourse,connectingwithprofessionalcourse•Mainline----conservationofenergy•Basedon:mathematics,physics,calculationmethod,fluidmechanics,engineeringthermodynamics,etal.Theimportanceandnecessityofthiscourse：•Temperaturedifferenceexistseverywhere.•Heattransferisthebaseofthetechnology,suchasenergyengineering,powerengineering,chemicalengineering,mechanicalengineering,electricalengineering,civilengineering,etal•Heattransfer,fluidmechanicsandengineeringthermodynamics-----threemainbasementforenergyandpowerengineeringChapter1Introduction1.Thecontentofheattransferasanengineeringcurriculum(2)Driveforceoftheheattransferprocess？Heatconduction,convection,radiation,andheatexchangeranalysisTheSecondLawofThermodynamicsTemperaturedifferenceHeattransfer-----sciencetorevealthelawofheattransferwhenatemperaturedifferenceexists.(1)Definition？2.ThreewaysofheattransferConductionConvectionRadiationResearchmethodNumericalmethodExperimentSeparationAnalogyvisualizationofnaturalconvectioninacirclespaceNumericalresultsofthetemperaturedistributioninaturbineTemperatureinanelectromotorCircumstanceinacarSoftwarestoresolvetheflowandheattransferissues:CHAMCompany(U.K.)PHOENICS，FLUENTCompany(U.S.)FLUENT,AEATechnology(U.K.)CFX,FlowScienceCompany(U.S.)FLOW-3D,ComputatioalDynamicsCompany(U.K.)STAR-CD,etal.3.ThedifferencebetweentheheattransferandthermodynamicsThermodynamics⇓Theconservationofenergyandthedirectioninwhichenergymaybetransferred,mostfrequentlythesituationsinequilibrium.Heattransfer⇓Themechanismsresponsibleforthetransferringenergyfromoneplacetoanotherwhenatemperaturedifferenceexists,bothequilibriumandnon-equilibriumprocesses.Thermodynamics：Heattransfer：mTQ(,,,)()TxyzQfττ=Water，M220oCIron,M1300oC4.ApplicationexamplesFigure1.1.1Moltenpolymerisdepositedasaliquidontoachillrollandremovedsomewheredownstream.4.ApplicationexamplesFigure1.1.2Aprocessforrecoveringsalt-freewaterfrombrine.4.ApplicationexamplesFigure1.1.3Radiantheatingofwaterflowinginsidesmalltubes.ThecoolingprocessofdrinksintherefrigeratorAirbrickwillbebenefittokeeptheroomtemperature.4.ApplicationexamplesNuclearreaction——Aconductionproblemwithinnerheatsource.Lasermachiningprocess4.ApplicationexamplesCoolingoftheelectronicunitForcedconvectionandnaturalconvectionAir-condition4.Applicationexamples厨师吹肉丝0065300.510030ttttθθ∞∞−−===−−一厨师在炒鸡肉丝时要品尝一下咸淡，于是他从100℃的热炒锅中取出一鸡肉丝，用口吹了一会，待其降至65℃时再放入口中。试估算厨师需要吹多长时间？出锅时鸡肉丝可视为平均直径为2mm的圆条，厨师口中吹出的气流温度为30℃，其与鸡肉丝之间的表面传热系数为，鸡肉丝的解：首先检验是否可用集中参数法。为此计算故可以采用集中参数法。所以由此解得冰冻三尺，非一日之寒•设地表温度为10℃，后受到冷空气侵袭，地表温度降为-15℃并维持不变，确定这种条件下，地面下1m处温度降为0℃所需的时间。解：土壤地物性取为于是所以有即查表得得天由上面的分析可知当地表温度很低时，地下还可以保持较高的温度。所以将水管埋在地下可防止水结冰。Automobilecrankcase----HeatlossfrombottomsurfaceexposedtoairstreamCoolingairdrawnoverelectronicdevicesmountedonboard.Devicesare4x4mminsize,spacing=0.25mm.Findthesurfacetemperatureofthefourthdevice,assumeduniformsurfaceT.T∞=27ºCV=10m/sQ=40mWeachdevice“turbulator”15mmCLSpecialcase1Specialcase2Example：Assumethatapersoncanbeapproximatedasacylinderof0.3-mdiameterand1.8-mheightwithasurfacetemperatureof24℃.Calculatethebodyheatlosswhilethispersonissubjectedtoa15m/swindwhosetemperatureis-5℃.121320.6RePrNu=+MoltenleadSpecialcase3:Freefallingliquiddrops人体为恒温体。若房间里气体的温度在夏天和冬天都保持20度，那么在冬天与夏天、人在房间里所穿衣服能否一样？为什么？夏天人在同样温度（如：25度）的空气和水中的感觉不一样。为什么？北方寒冷地区，建筑房屋采用双层玻璃以利于保温。如何解释其道理？越厚越好？为什么冬天人脸的耳朵和鼻子最凉？日常生活中的例子能源动力、制冷、建筑环境、化工、机械制造、新能源、微电子、核能、航空航天、微机电系统（MEMS）、新材料、纳米技术、军事科学与技术、生命科学与生物技术…技术领域中大量存在传热问题AN-124协和式超音速客机AN-225Turbojet:涡轮喷气发动机航空发动机高温叶片冷却冷却技术失效时STS-110AtlantislaunchonApril8th2002火箭发动机神州5号神州6号顺利返回烧蚀防热火箭发动机火箭发动机推力室发汗冷却电阻电火箭电阻电热推进器冲压发动机X-51效果和构造示意图高超音速导弹鼻锥发汗冷却预警飞机金属泡沫换热器在预警飞机上的应用航空母舰上飞机的热防护热管散热器新材料热能工程系工程热物理研究所BlastFurnace（高炉）热能工程系工程热物理研究所CastingProcess锅炉汽轮机发电机给水泵凝汽器超临界压水堆超临界二氧化碳快速气冷堆热泵与制冷系统HeatcompressorExpansiondevicecondenserevaporatorcabinet太阳直太阳直射辐射射辐射大气长大气长波辐射波辐射太空散太空散射辐射射辐射对流对流换热换热地面反射辐射地面反射辐射环境长波辐射环境长波辐射地面长地面长波辐射波辐射壁体得热壁体得热室内表面与空气的热平衡关系示意室内表面与空气的热平衡关系示意JPX2幻灯片47JPX2JPX,2006-11-6Applicationsofporousmediahydrogen storage metalFuel CellElectrical CoolingPorous StructuresTranspirationcooling MicroscaleRocket2010‐9‐1949•Transpirationcooling–Rocketengine–Gasturbine–Scramjetfuelinjector2010‐9‐1950•HeattransferenhancementCPUCoolingPowerfullLasermirrorCooling2010‐9‐1951•Fuelcells•CCS2010‐9‐195253•PhononTransportOutsideNanostructuresPhononRarefactionSourceGateDrainHeatFlowHostWire•ThermalConductivityofNanocomposites•PhononTransportInsideNanostructurest0δxQ800°C20°C5HeattransferprocesssteadysteadyNonNon--steadysteadyt0δxHeatedto800°Csuddenly20°C