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

在受控扰动的作用下，层流水膜上产生了二维波。并在室温下实验测定了薄膜对周围气体吸收速率的增大。在10-30赫兹的波频范围内，薄膜的整个表面都出现了二维波，否则两个波相互融合成为三维的。在低雷诺数Re&t；20时，增大随波频单调减小，而在高雷诺数Re&gt；20时增大。考虑到这些结果以及长崎和Hijikata(1990)等人的数值观测，建立了双边界层模型，其中传质系数α表示为α=xiroo&lt；3.46Dlpif_w&gt；其中D和f_w是扩散系数和波频。结果表明，在给定的液体物理性质下，该参数只是波速的函数，且随波速单调增大。

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.