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1、RemsburgR.“FluidDynamicsforElectronicEquipment”ThermalDesignofElectronicEquipment.Ed.RalphRemsburgBocaRaton:CRCPressLLC,2001?2001byCRCPRESSLLC0082-03-IPage85Wednesday,August23,20009:55AMFluidDynamicsfor3ElectronicEquipment3.1INTRODUCTIONTofullyunderstandhe
2、attransferbynaturalorforcedconvection,havingabasicunderstandingof?uiddynamicsisnecessary.Moreadvancedcoolingtechniquesthatinvolve?uiddynamicsincludeliquidimmersion,multiphasecooling,andjetimpingement.Thegeneralterm?uidconveysanysubstancethatdoesnothaveafor
3、m.Liquidsandgasesareboth?uids.Further,todifferentiateliquidsfromgases,liquidshaveasurface,whereasagaswillexpandto?llavolume.Liquidsaregenerallyconsiderednearlyincompressible,whereasgasesarereadilycompressible.Thevastmajorityofcoolant?owsareoftheincompressi
4、bletype.However,theequationsmayrequirecorrectionforthepropertiesofacompressible?uidduetothealtitude.Thistextemphasizesincompressible?ow.3.2HYDRODYNAMICPROPERTIESOFFLUIDS3.2.1COMPRESSIBILITYAltitudeaffectsthedensityoftheairduetocompressibility.Alongwiththec
5、hangeindensity,importantchangesarefoundinhowmuchheattheaircanabsorb,turbu-lence,heattransfercoef?cients,andmanyotherparameters.Theapplicationofpres-surecancompressallmaterials,withtheresultbeingthestorageofelasticenergy.Assumingperfectenergyconversion,them
6、aterialsexpandtotheiroriginalvolumeswhentheyreleasethepressure.Fluidsdonothavetherigidityofsolidmaterials,sothechangeinvolumede?nesthemodulus.ThechangeinvolumeiscalledtheBulkModulus.With?uids,espe-ciallygases,thecurveplottedbythebulkmodulusbecomessteeperwi
7、thincreasingpressure.Thisshowsthataswecompressthe?uid,itbecomesmoredif?culttocompressitfurther.Thebulkmodulusofa?uidisgivenby:??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
