Study on the Enhancement of Gas Absorption into a Falling Liquid Film Caused by Surface Waves and Modelling of the Gas Absorption

为了理解为什么表面波能极大地增强气体在下降液膜中的吸收并建立吸收模型，我们研究了三维表面波在下降液膜上的动力学。本次调查的主要结果可以总结如下。通过在膜入口引入可控的恒频扰动，在垂直表面上的水膜上激发分离良好的表面波（孤立波），并分析了表面波对膜入口下方扰动产生的空间扰动的响应。结果表明，小相速度的二维波在大波长空间扰动下不稳定，转化为具有正弦波阵面的三维波，而中、大相速度的波在小波长扰动下不稳定，波阵面在每个波阵面上弯曲形成多个u形。U形（或s）源于扰动，U'，它们与相应的扰动排成一行。当在薄膜上施加单个扰动时，由该扰动产生的“U”会导致两侧产生新的“U”，即发生自诱导的横向传播。指出这些表面波具有发生在以固体表面和自由液气界面为界的剪切层中的涡旋，其u形波类似于在壁面边界层中观测到的lambda -涡旋和马蹄形涡旋。

To understand why the surface waves drastically enhance the gas absorption into a falling liquid film and model the absorption, we investigated the dynamics of three-dimension surface waves on the falling liquid film. The major results of this investigation may be summarized as follows.Surface waves separated well from each other (solitary waves) were excited on a water film falling down a vertical surface by introducing controlled temporal disturbances of constant frequencies into the film entrance, and the response of the waves to spatial disturbances generated by perturbations located just below the film entrance is analyzed. The results show that the two-dimensional waves of small phase velocities are unstable to spatial disturbances of large wavelengths and transform into three-dimensional waves having sinusoidal wave fronts, while the waves of intermediate and large phase velocities are unstable to small wavelength disturbances and their wave fronts bend to form several U-shapes on each front. The U-shapes (or ' s) originate from the perturbations, U' and they align in a row with the corresponding perturbations. When a single perturbation is put on the film, a 'U' orginating from the perturbation leads to the generation of a new 'U' on either side, i.e.a self-induced lateral propagation occurs.It is pointed out that these surface waves hold vortices occurring in a shear layr bounded by a solid surface and a free liquid-gas interface, and the U-shaped waves resemble both the LAMBDA-vortices and horseshoe-shaped vortices observed in boundary layrs on walls.