Non-absorbable gas effects on heat and mass transfer in wavy laminar falling film absorptin

Abstract

Absorption of water vapor in a liquid film is an important process in a proposed solar cooling system. Film absorption involves simultaneous heat and mass transfer in the gas—liquid system. The heat of absorption gives rise to temperature gradients leading to the transfer of heat while temperature affects the vapor pressure-composition equilibrium at the interface between the two phases which in turn influences mass transfer. The composition of the gas phase, in which a non-absorbable gas is combined with the absorbate, also influences the combined heat and mass transfer. The non-absorbable gas, in conjunction with the absorbate, is transported by convection and diffusion toward the liquid-gas interface. Since the interface is impermeable to the non-absorbable gas, the concentration of the non-absorbable gas at the interface is significantly greater than that in the bulk of the gas resulting in a reduction in absorbate mass transfer. An experimental program has been utilized to study this non-absorbable gas effect on the combined heat and mass transfer in film absorption. As expected from numerous previously reported studies, the experimental results indicate that significant increases in the heat and mass transfer rates can be obtained by reducing the non-absorbable gas concentration to levels approaching 0%. The Sherwood number and film Nusselt number are correlated using the film Reynolds number, Prandtl number, Schmidt number, Lewis number and air concentration. These effects are shown to have similar trends when compared to a numerical solution of the smooth falling film problem in which the absorbent and absorbate flow concurrently.