Enhancement of Heat and Mass Transfer through Falling Liquid Film by Surface Wave Control

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From experimental measurement of oxygen absorption into falling water film imposed periodic disturbances, it has been clarified that an optimum wave exists for absorption enhancement. Numerical simulations have been carried out for wave evolution on falling liquid film and for steam absorption by wavy falling film of LiBr aqueous solution, where developments of the waves, absorption at the interface, and heat and mass transfer in the film are solved simultaneously. Small disturbance waves given at the inflow boundary, grow into developed waves. Wave evolution is classified into three categories, according to wave frequency. Streamlines, concentration and temperature fields in the wavy film are shown. Recirculation which appears in a large wave involves low, concentration solution near the interface and discharges it at the wave rear. Absorption rate is very high in the area of capillary waves accompanies with the large wave and it is minute in the region between the front and crest of the large wave. Velocity field around wave trough in front of large wave becomes complicated and back flow is generated.