2025/6/21112.1Two-phaseflowpatternandheattransfer
第一节两相流的流型与传热Flowpatternoftwo-phaseflow汽水两相流体的流型Heattransferinwater-cooledwall水冷壁管内的传热Parametersoftwo-phaseflow汽水两相流的特性参数Velocity两相流体的速度Steamqualitybymass两相流体的含汽率Density两相流体的密度
2025/6/21212.1Two-phaseflowpatternandheattransfer
第一节两相流的流型与传热1.蒸发管内的汽水两相流型Two-phaseflowpattern
2025/6/21312.1Two-phaseflowpatternandheattransfer
第一节两相流的流型与传热Fig.2isaclassicpictureofboilingwaterinalong,uniformlyheated,circulartube.Floworforcedconvectiveboiling,whichisfoundinvirtuallyallsteamgeneratingsystems,isamorecomplexphenomenoninvolvingtheintimateinteractionoftwo-phasefluidflow,gravity,materialphenomenaandboilingheattransfermechanisms.Thewaterentersthetubeasasubcooledliquidandconvectionheattransfercoolsthetube.Thepointofincipientboilingisreached(point1inFig.2).Thisresultsinthebeginningofsubcooledboilingandbubblyflow.欠焙水内管子下部进入，完全蒸发后生成的过热蒸汽由上部流出。如受热不太强烈，区域A为单相水的对流传热，水温低于饱和温度，管壁金属温度稍高于水温。在B区内，紧贴壁面的水虽到达饱和温度并产生汽泡，但管子中心的大量水仍处于欠热状态．生成的汽泡脱离壁面后又凝结并将水加热，这区域内的壁温高于饱和温度，进行着过冷核态沸腾传热。
2025/6/21412.1Two-phaseflowpatternandheattransfer
第一节两相流的流型与传热Fluidtemperaturecontinuestoriseuntiltheentirebulkfluidreachessaturationtemperatureandnucleateboilingoccurs,point2.Atthislocation,flowboilingdepartssomewhatfromthesimplepoolboilingmodelpreviouslydiscussed.Thesteam-watermixtureprogressesthroughaseriesofflowstructuresorpatterns:bubbly,intermediateandannular.Thisisaresultofthecomplexinteractionofsurfacetensionforces,interfacialphenomena,pressuredrop,steam-waterdensitiesandmomentumeffectscoupledwiththesurfaceboilingbehavior.当水进入C区时全部达到饱和温度，传热转变为饱和核态沸腾。此后生成的汽泡不再凝结，沿流动方向的含汽量逐渐增大，汽泡分散在水中，这种流型称为汽泡状流。
2025/6/21512.1Two-phaseflowpatternandheattransfer
第一节两相流的流型与传热Whileboilingheattransfercontinuesthroughout,apointisreachedintheannularf