Dynamics of surface waves on films falling down horizontal tubes and associated gas absorption

对一种液膜沿水平管下落并吸收周围气体的气体吸收器进行了实验和理论分析，并与垂直管气体吸收器的分析结果进行了比较。假设浓度边界层从管的顶部开始沿光滑表面发展到管的底部，从理论上分析了水平管中光滑膜的下降和伴生气体的吸收。当管间距小于毛细常数时，液体在管间形成片状，并在管内连续流动，形成几乎均匀的薄膜，沿各管下落。当管间距变宽时，液体从每根管上滴下，产生振幅较大的波，这些波在覆盖下一根管的薄膜上迅速传播。水滴使薄膜在较低的管子上流动更不均匀。与管间的片状流动相比，水滴引起的波增强了伴生气体吸收50%或更多。在雷诺数Re<30时，对上管进料流施加周期性扰动使管间片流膜的气体吸收率提高了约20%。在直径为6mm管的薄膜上观察到瑞利不稳定性，并增强了气体吸收。在水平管上的膜流中，水滴完全更新了浓度边界层，并在下管顶部开始形成新的边界层。在水平管上的膜流中，膜流的气体吸收率比垂直管上的膜流大，垂直管上的滚波大大增强了气体吸收率。

A gas absorber, in which liquid films fall down horizontal tubes and absorb surrounding gas, was experimentally and theoretically analyzed, and the analytical results were compared with those of a vertical-tube gas absorber.Smooth film falling down horizontal tubes and the associated gas absorption were theoretically analyzed, assuming that a concentration boundary layer starts at the top of tube and develops along the smooth surface to its bottom.When the tube spacings are smaller than the capillary constant, liquid forms sheets between tubes and continuously flows in them, and forms nearly uniform films falling down all tubes.With wider tube spacings, liquid drips off each tube and causes the large-amplitude waves which rapidly spread on the film covering the lower tube.The drip makes the films flow more unevenly on lower tubes.The drip-caused waves enhance, the associated gas absorption by 50% or more, compared with the sheet flow between tubes.Imposing periodical perturbations on feeding flow to the top tube enhances the gas absorption of films with the sheet flow between tubes by 〜20% at the Reynolds number Re<30.Rayleigh instability was observed on films covering 6 mm diameter tubes and enhanced the gas absorption. The film flow on horizontal tubes, in which the drip completely renews concentration boundary layers and a new boundary layer starts at the top of lower tube, has larger gas absorption rate than the films falling down vertical tubes on which roll waves greatly enhance the gas absorption.