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1、学校代码：10128学号：本科毕业论文外文翻译（题目：空冷热交换器和空冷塔学生姓名：学院：电力学院系别：能源与动力工程专业：热能与动力工程班级：动本2003②指导教师：二〇〇七年六月Air-cooledHeatExchangersandCoolingTowersD.G.KROGERSc.D.(MIT)(ThistextisapartofMRKROGER'sbook.include8.4,9.3,9.4)8.4RECIRCULATIONHeatedplumeairmayrecirculateinan
2、air-cooledheatexchanger,therebyreducingthecoolingeffectivenessofthesystem.Figure8.4.1depicts,schematically,across-sectionofanair-cooledheatexchanger.Intheabsenceofwind,thebuoyantjetorplumerisesverticallyabovetheheatexchanger.Apartofthewarmplumeairmayh
3、oweverbedrawnbackintotheinletofthetower.Thisphenomenonisknownas"recirculation".Plumerecirculationisusuallyavariablephenomenoninfluencedbymanyfactors,includingheatexchangerconfigurationandorientation,surroundingstructuresandprevailingweatherconditions.
4、Becauseofhigherdischargevelocities,recirculationisusuallylessininduceddraftthaninforceddraftdesigns.Figure8.4.1:Air-flowpatternaboutforceddraftair-cooledheatexchanger.Lichtenstein[51LI1]definesarecirculationfactoras(8.4.1)wheremristherecirculatingairm
5、assflowrate,whilemaistheambientairflowrateintotheheatexchanger.Althoughtheresultsofnumerousstudiesonrecirculationdoappearintheliterature,mostareexperimentalinvestigationsperformedonheatexchangershavingspecificgeometriesandoperatingunderprescribedcondi
6、tionse.g.[74KE1,81SL1].GunterandShipes[72GUlldefinecertainrecirculationflowlimitsandpresenttheresultsoffieldtestsperformedonair-cooledheatexchangers.Problemsassociatedwithsolvingrecirculatingflowpatternsnumericallyhavebeenreported[81EP1].Krogeretal.in
7、vestigatedtheproblemanalytically,experimentallyandnumericallyandrecommendaspecificequationwithwhichtheperformanceeffectivenessofessentiallytwo-dimensionalmechanicaldraftheatexchangersexperiencingrecirculation,canbepredicted[88KR1,89KR1,91DU1,93DU1,95D
8、U1].8.4.1RECIRCULATIONANALYSISConsideronehalfofatwo-dimensionalmechanicaldraftair-cooledheatexchangerinwhichrecirculationoccurs.Forpurposesofanalysis,theheatexchangerisrepresentedbyastraightlineatanelevationHiabovegroundlevelasshowninfigure8.4
