竖直平板表面流动液膜厚度的实验研究

液膜厚度是研究液膜流动特性的重要参数，为了得到液膜流动过程中厚度的变化规律，对竖直平板表面上由重力驱动的水膜流动进行实验测量。自主设计并搭建降液膜流动实验台，利用电容式液膜测厚仪统计分析层流流动，距离入口25cm处的流动液膜厚度随时间的演化状况。实验结果表明：在时间域上，观测点的液膜厚度值不断发生变化。Re=297时，0至70 s内的流动液膜的波动性平稳，厚度平均值接近168.5um 。Re=462与Re=627时，在0至40 s时间段内波动较强烈，40至70 s的液膜流动趋于平稳状态。Re=814时，所测时间段0-70 s，液膜波动较剧烈，波动幅度增大。液膜厚度与雷诺数呈正线性相关关系。当Re=814时，每个时间点的液膜厚度在360um以上，高于其他三种不同雷诺数时的液膜厚度。高雷诺数时液膜的波动状况更加剧烈，减小雷诺数有利于形成光滑的液膜。从侧面体现出流动液膜具有不稳定性。

Experimental study on the thickness of flowing liquid film on vertical flat surface

The thickness of liquid film is an important parameter to study the flow characteristics of liquid film. In order to obtain the thickness change rule of liquid film flow, the gravity driven water film flow on the vertical plate surface was measured experimentally.. A falling film flow test rig was designed and built independently. The laminar flow was analyzed by capacitive liquid film thickness gauge. The thickness of the falling film at the distance of 25 cm from the inlet changed with time. The experimental results show that in the time domain, the liquid film thickness of the observation points is constantly changing. When Re=297, the flow liquid film in 0 to 70 s fluctuates smoothly, and the average thickness is close to 168.5um. When Re = 462 and Re = 627, the fluctuation is strong in 0-40 s, and the liquid film flow tends to be stable in 40-70 s. At Re=814, the liquid film fluctuated more sharply and the fluctuation amplitude increased when 0-70 s was measured. The thickness of liquid film has a positive linear correlation with Reynolds number. When Re = 814, the liquid film thickness at each time point is above 360 um, which is higher than that at the other three different Reynolds numbers. When the Reynolds number is high, the fluctuation of the liquid film is more intense. The reduction of Reynolds number is conducive to the formation of a smooth liquid film. The flow liquid membrane shows instability.