(传热英文课件)chapter 9(condensation and boiling heat transfer).ppt

examples Rohsenow correlation Forced convection boiling for full developed nucleate boiling calculation Peak heat flux for nucleate pool boiling Zuber correlation Other correlation and the applicable conditions are shown in the books Stable film boiling Bromley correlation(stable film boiling region on horizontal tubes) Total heat transfer coefficient (hr is the radiation heat transfer coefficient) Where hr is the radiation heat transfer coefficient , Reference temperature 9-6 simplified relations for boiling heat transfer with water the heat pipe tgcavszhjdbvnm f High heat-transfer coefficient Low temperature difference Reliability Adjustable heat flux Temperature control(space) Heat transfer(High-power electronic components) The characteristics of heat pipe Application Chapter 9 condensation and boiling heat transfer 9-1 introduction The heat transfer convection we discussed before is considered homogeneous single-phase systems. For convection associated with a change of phase of fluid .usually we deal with two conditions. condensation boiling 9-2 condensation heat-transfer phenomena When temperature of the plate below the saturation temperature of the vapor, with the action of the gravity . The condensate form and flow down the surface . Filmwise condensation : the liquid can wet the surface , a smooth film formed ;the thickness of the film on the surface grows as it goes down the plate , there is a gradient exists in the film. The film also presents thermal resistance to heat transfer. Dropwise condensation: the liquid can’t wet the surface, droplets formed on the surface , the surface is not completely covered by the liquid , and when droplets goes down ,they can take many droplets in their way with them , so dropwise condensation has no film barrier for heat flow , and its heat transfer rates may be as much as 10 times higher th