Heat and mass transfer in film absorption in the presence of non-absorbable gases

This paper is concerned with the effect of non-absorbable gases on the combined heat and mass transfer process in film absorption. Some simple models of the phenomenon have been proposed before which have under-predicted the mass flux. Here, a detailed theoretical model has been developed for the film, taking into consideration bulk movements in the vapor and liquid phases in the direction perpendicular to the film flow, which occur to compensate for the molal flux due to concentration gradients in the absorbent and vapor. The energy and diffusion equations were solved analytically for the entrance region in both the liquid and gas phases to give the temperature and concentration distributions, from which heat and mass fluxes may be determined. The reduction in mass flux due to non;absorbable gases is related to the need for the absorbate to diffuse through a thin layer of these gases blocking its access to the interface, before it can be absorbed. This reduction was found to depend most critically on the ratio of resistance to absorbate diffusion between the liquid and the gas. Even a small amount of non-absorbables can inhibit absorption significantly. Particular cases including isothermal absorption have been considered and the effect of the heat of absorption and other process parameters has been studied. (C) 1997 Elsevier Science Ltd.