建筑环境与能源应用工程专业英语5.ppt

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1、LessonFiveHeatTransferTopicsWordslearning1Introducitonofheattransfer2Workingsitepictures33Textlerning44heattransferequipment传热设备heatexchanger热交换器boiler锅炉condenser冷凝器radiator散热器refrigerator冰箱solarcollector太阳能集热器heattransferrate传热(速)率temperaturedifference温差factorofsafety安全系数experiment

2、alerror实验误差operatingcondition运行条件heattransfercoefficient传热系数undertheseadverseconditions在最不利工况下threeformsofheattransfer:conduction传导convection对流radiation辐射heattransferequipment传热设备heatexchanger热交换器boiler锅炉condenser冷凝器radiator散热器refrigerator冰箱solarcollector太阳能集热器heattransferrate传热(速)率

3、temperaturedifference温差factorofsafety安全系数experimentalerror实验误差operatingcondition运行条件heattransfercoefficient传热系数undertheseadverseconditions在最不利工况下threeformsofheattransfer:conduction传导convection对流radiation辐射Topicone:FrequentlyusedwordsandphrasesHeatSensibleHeatLatentHeatduetomolecular

4、thermalmotionSolidificationfusionLiquefactionevaporationTopictwo:IntroducitonofheattransferConductionConvectionRadiationThreeformsofheattransferForsteady-stateheatconductioninonedimension,theFourierlawistemperaturegradientcross-sectionalareanormaltoflowthermalconductivityheatflowrat

5、eEquation(1)statesthattheheatflowrateqinthexdirectionisdirectlyproportionaltothetemperaturegradientdt/dxandthecross-sectionalareaAnormaltotheheatflow.Theproportionalityfactoristhethermalconductivityλ.Theminussignindicatesthattheheatflowispositiveinthedirectionofdecreasingtemperature

6、.Conductivityvaluesaresometimesgiveninotherunits,butconsistentunitsmustbeusedinEquation(1).(1)Thefundamentalequationforunsteady-stateconductioninsolidsorfluidsinwhichthereisnosubstantialmotioniswherethermaldiffusivityαistheratioλ/ρcp;λisthermalconductivity;ρ,density;andcp,specifiche

7、at.Ifαislarge(highconductivity,lowdensityandspecificheat,orboth),heatwilldiffusefaster.Isthereanymistakes?Heattransferinvolvingmotioninafluidduetothedifferenceindensityandtheactionofgravityiscallednaturalconvectionorfreeconvection.Heattransfercoefficientsassociatedwithgasesfornatura

8、lconvectionaregener