水平管外降膜厚度分布规律的数值模拟研究

Numerical Simulation Study of the Law Governing the Distribution of the Falling-film Thickness Outside a Horizontal Tube

液膜厚度分布规律对水平管降膜蒸发过程有重要的影响。本研究建立了水平管外降膜流动的CFD模型,通过模拟不同入口流速、管径大小的液膜厚度来研究冷态情况下管外液膜厚度的影响因素及其沿环向角的分布规律。模拟结果表明:对于固定管径,液膜厚度随着入口速度的增大而增大;在入口速度一定时,管外液膜厚度在管顶区域较大,在周向105°附近达到最小值;且液膜厚度随着管径的增大而缓慢减小,当入口速度减小到一定程度时,管壁会出现"干涸"现象。

The law governing the distribution of the liquid film thickness exercises an important influence on the falling film evaporation process outside a horizontal tube. A CFD model for the falling film flow outside a horizontal tube was established and through simulating the liquid film thickness at various inlet speeds and different sizes of the diameter of the tube,the factors influencing the liquid film thickness outside the tube in the cold state and the law governing its distribution along the circumferential angle were studied. The simulation results show that for a constant diameter of the tube,the liquid film thickness will increase with an increase of the inlet speed. When the inlet speed is constant,the liquid film thickness outside the tube will be relatively big in the zone at the top of the tube and arrive at its minimum around a place at a circumferential angle of 105 degrees. Moreover,the liquid film thickness will gradually decrease with an increase of the tube diameter. When the inlet speed decreases to a certain extent,the'dry-up'phenomenon will appear on the tube wall