Enhancement of Mass Transfer into a Falling Liquid Film by Two-Dimensional Waves

在有可控扰动输入的层流水膜上激发二维波。并在室温下实验测定了波对膜对周围气体吸收率的提高。在10-30Hz的波频率范围内，二维波出现在整个薄膜表面，其他波相互合并成为三维波。在低雷诺数Re<20时，随波频的增加，增大量呈逐波递减。而在高雷诺数时则增大。二维波的吸收率随雷诺数的增加而增加。在雷诺数为Re>50时，其速率是平面膜的2.5倍。根据这些结果和Nagasaki和Hijikata（1990）等人的数值观测，建立了双边界层模型，其中传质系数alpha表示为alpha=xiROO<3.46Dlpif_w>，其中D和f_w分别为扩散系数和波频，引入了波xi对近地表高浓度层的扫描运动参数。结果表明，在给定的流体物理性质下，该参数仅是波速的函数，并随波速单调增加。

Two-dimensional waves are excited on a falling laminar water film with input of controlled disturbances. and the augmentation in absorption rate of the film from the surrouding gas by the waves are experimentally determined at the room temperature. Two-dimensional waves appear on the whole surface of the film in the range of wave frequencies 10-30Hz, and otherwise waves coalesce with each other to become three dimensional. The augmentation decreases momotonecally with wave frequency at low Reynolds numbers Re<20. while increases at high Reynolds numbers Re>20. Two-dimensional waves increase in absorption rate with Reynolds number. and the rate becomes 2.5 times larger than the values for flat surface films at Reynolds numbers Re>50.Taking account of these results and the numerical observations by Nagasaki and Hijikata (1990) and others, the double boundary layr model is built up, inwhich the mass transfer coefficient alpha is expressed as alpha=xiROO<3.46Dlpif_w>, where D and f_w are diffusivity and wave frequency, introducing the parameter for sweeping motion of high concentration layr near the surface by the waves xi. It is found that the parameter is a function only of wave velocity at the given physical properties of the liquid and increases monotonically with wave velocity.