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大大增强气体吸收到一个下降的液体膜和模型的吸收，我们研究了三维表面波的动态下降的液体膜。本文的主要研究结果可以概括如下：通过在垂直表面上下落的水膜入口处引入恒定频率的受控时间扰动，在水膜上激发出相互分离的表面波（孤立波），并分析了孤立波对空间扰动的响应。结果表明，小相速的二维波对大波长的空间扰动不稳定，并转变为具有正弦波前的三维波;中、大相速的波对小波长扰动不稳定，其波前在每个波前上发生弯曲，形成多个U形。U形（或“s”）源自扰动U'，它们与相应的扰动排成一行。当在膜上施加一个扰动时，由扰动产生的“U”导致在两侧产生一个新的“U”，即发生自诱导横向传播.本文指出，在由固体表面和自由液-气界面所围成的剪切层中，这些表面波包含着涡，U形波既类似于在壁面边界层中观察到的LAMBDA涡，也类似于马蹄形涡。

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.