多相流基础.ppt

Other geometries（其他非圆通道内流型） Rectangular channels（矩形通道） —— Flow patterns are very similar to those in round tubes ——Liquid tends to collect in the corners Vertical downflow (in tubes)（垂直下降圆形通道） —— When gas and liquid phase are both flowing downwards annular flow occurs very frequency. Obstructions on the wall（壁面有障碍物） —— There is a tendency for the liquid to be thrown into the center of the channel Helical twisted tape insert（螺旋状插入物） —— This tend to throw the liquid on to the walls of the tube —— produce good heat transfer (heat transfer advanced method) Helically coiled tube（螺旋盘旋管） —— This tends to throw liquid onto the walls of the tube at point A or point B or somewhere in between (on ACB) due to the effect of gravity. Rod bundles （as in nuclear reactors）（棒束通道） —— similar to those found in round Chapter two — Two-phase flow patterns and flow pattern maps（第二章－两相流型和流型图） —— gas-liquid two-phase flow has obvious interface（气液两相流动具有明显的流动界面） —— has various geometric configurations（流动具有各种不同的几何构型） 1、Flow pattern or flow regime（流型） Introduction（简介） 2、Important physical parameters in determining the flow pattern:（流型） —— surface tension（表面张力） Keep channels walls always wet Make small liquid drops and small gas bubbles spherical —— gravity（重力） Tends to pull the liquid to the bottom of the channel especially in non-vertical channel …… 3、Flow patterns in vertical upward tubes ——gas and liquid phase both flowing upwards，adiabatic flow（垂直上升管内的流型 —— 气液两相均向上流，绝热流） ——When the quality is gradually increased from 0 to 1, the flow patterns can be classified: （1）Bubbly flow（泡状流） Liquid phase is the continuous phase Gas or vapor phase is the dispersed phase Gas or vapor bubbles are of approximately uniform size. （2）Plug flow or Slug flow（弹状流） Gas flows as large bullet-shaped bubbles（sometimes called Taylor bubble） Gas bubble and liquid slug flow across tube alternatively Some small gas bubbles distributed throughout the liquid phase. （3）Churn flow（搅拌流，块状流） Highly unstable flow，oscillat