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1、4ppliedEnergy33(1989)235-252Heat-ExchangerPerformance:EffectofOrientationC.W.LeungDepartmentofMechanicalandMarineEngineering,HongKongPolytechnic,HungHorn,HongKong&S.D.ProbertDepartmentofAppliedEnergy,CranfieldInstituteofTechnology,BedfordMK430AL,UKABSTRACTForanextende
2、d-surfacenatural-convectivetypeheat-exchangerinair,withitsbaseatupto40°Cabovethetemperatureoftheambientenvironment,thesteady-stateheat-transferperformancesofthethreemostcommonlyemployedorientationsofthereetangularfinsandbase(namelyverticalfinsperpendiculartoaverticalb
3、ase,orprotrudingverticallyi4pwardsfromahorizontalbase,orhorizontalfinsattachedtoaverticalbase)havebeenconsidered.Thelatterconfigurationisofnopracticalinterestfortheintendedpurposebecauseofitsrelativelyinferiorheat-transfercapabilities.Ifanoptimalinter-finseparationofa
4、pproximately10mmisadopted,allotherconditionsremaininginvariant,ahigherheat-transferrateperunitbaseareaisusuallyachievedfromthearrayoffinswhentheyareattachedorthogonallytothevertical,ratherthanthehorizontal,base;butthisisnotunequivocallyso~Morethan300setsofexperimental
5、data,obtainedfromseveraldifferentarraysofverticalrectangularhighlypolishedduraluminfinsprotrudingorthogonallyeitherfromavertical,orupwardsfromahorizontal,rectangularhighlypolishedduraluminbasewereassessed.Thenon-dimensionaldatacorrelationsthatemergedenabletheaverageco
6、efficientforheat-transferfromafinnedsurfaeetotheambientenvironment,forallthefinnedsurfaeesinthesetwotypesofconfiguration,tobeeasilypredicted.235AppliedEnergy0306-2619/89/$03"50O1989ElsevierSciencePublishersLtd,EnglandPrintedinGreatBritain236C.W.Leung,S.D.ProbertNOTATI
7、ONaPowerindexineqn(21)bRectangularfins'protrusion(seeFig.1)(m)CNumericalconstantineqn(21)Specificheatofair(Jkg-'K-')gAccelerationduetogravity(ms-2)Gr(=gflOs3/v2),aGrashofnumberfortheairflowGr'(=gflOs3/v2{s/[(bZ)'/2]}exp{-kb/kr6}),amodifiedGrashofnumberh(=Q/{OL[W+2b(n+
8、1)]}),overallheat-transfercoefficientbe-tweenthefinnedsurfaceanditsambientenvironment(Wm-ZK-1)kThermalconductivityofair,eval
