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1、RemsburgR.“FluidDynamicsforElectronicEquipment”ThermalDesignofElectronicEquipment.Ed.RalphRemsburgBocaRaton:CRCPressLLC,2001©2001byCRCPRESSLLC0082-03-IPage85Wednesday,August23,20009:55AMFluidDynamicsfor3ElectronicEquipment3.1INTRODUCTIONTofullyunderstandhe
2、attransferbynaturalorforcedconvection,havingabasicunderstandingoffluiddynamicsisnecessary.Moreadvancedcoolingtechniquesthatinvolvefluiddynamicsincludeliquidimmersion,multiphasecooling,andjetimpingement.Thegeneraltermfluidconveysanysubstancethatdoesnothaveafor
3、m.Liquidsandgasesarebothfluids.Further,todifferentiateliquidsfromgases,liquidshaveasurface,whereasagaswillexpandtofillavolume.Liquidsaregenerallyconsiderednearlyincompressible,whereasgasesarereadilycompressible.Thevastmajorityofcoolantflowsareoftheincompressi
4、bletype.However,theequationsmayrequirecorrectionforthepropertiesofacompressiblefluidduetothealtitude.Thistextemphasizesincompressibleflow.3.2HYDRODYNAMICPROPERTIESOFFLUIDS3.2.1COMPRESSIBILITYAltitudeaffectsthedensityoftheairduetocompressibility.Alongwiththec
5、hangeindensity,importantchangesarefoundinhowmuchheattheaircanabsorb,turbu-lence,heattransfercoefficients,andmanyotherparameters.Theapplicationofpres-surecancompressallmaterials,withtheresultbeingthestorageofelasticenergy.Assumingperfectenergyconversion,them
6、aterialsexpandtotheiroriginalvolumeswhentheyreleasethepressure.Fluidsdonothavetherigidityofsolidmaterials,sothechangeinvolumedefinesthemodulus.ThechangeinvolumeiscalledtheBulkModulus.Withfluids,espe-ciallygases,thecurveplottedbythebulkmodulusbecomessteeperwi
7、thincreasingpressure.Thisshowsthataswecompressthefluid,itbecomesmoredifficulttocompressitfurther.Thebulkmodulusofafluidisgivenby:PBV-------V-©2001byCRCPRESSLLC©2001byCRCPRESSLLC0082-03-IPage86Wednesday,August23,20009:55AMwhere:Bbulkmodulus(N/m2)Vori
8、ginalvolume(m3)pchangeinpressure(N/m2)Vchangeinvolume(m3)Valuesofthebulkmodulusarepositive.Inthepreviousequation,thenegativesigncompensatesforthefactthatthevolumeiscompressing.Thebulkmodulusofmostliquidsi
