ENHANCEMENT OF MASS-TRANSFER INTO A FALLING LAMINAR LIQUID-FILM BY TWIG-DIMENSIONAL SURFACE-WAVES - SOME EXPERIMENTAL-OBSERVATIONS AND MODELING

Two-dimensional surface waves were produced on a falling laminar water film by input of controlled disturbances, and the increase in the fil m absorption of the surrounding gas was determined at temperatures, 17 .1-18.4 degrees C. The augmentation decreases constantly with wave fre quency for low Reynolds numbers Re < 20, whereas it constantly increas es for higher Reynolds numbers Re > 20. Taking account of these experi mental results and the numerical observations by Nagasaki and Hijikata (1990, Proceedings of the 3rd Japan Mechanical Engineering Society Sy mposium on Numerical Dynamics, No. 900-69, pp. 47-48) and others, we c onstructed a double boundary layer model, in which the mass transfer c oefficient k(L) is expressed as k(L) = xi root 3.46Df(w)/pi, where D a nd f(w) are the diffusivity in the film and the frequency of the waves , respectively. The equation, which is derived from the penetration th eory, introduces the parameter xi for waves sweeping highly concentrat ed thin layers on the surface. It was found that at constant physical properties of liquid the parameter is a function only of phase velocit y, and thus increases with phase velocity.