Simultaneous heat and mass transfer in film absorption with the presence of non-absorbable gases

Numerical solutions are presented for the effect of a non-absorbable gas on the heat and mass transfer rates during the absorption of water vapor by a falling laminar smooth film of an aqueous lithium bromide or aqueous lithi um chloride solution (absorbent). The geometry consists of a vertical chann el with two walls, one of which is isothermal and the other adiabatic. The liquid film of air absorbent flows down over the isothermal wall, while a m ixture of water vapor and air flows between the liquid fi-ce-surface and th e adiabatic, wall. The whole system is kept under vacuum pressure. Water va por is absorbed by the film and air is the non-absorbable gas. The momentum , energy, and concentration equations are written with a set of interfacial and boundary conditions and solved numerically for the two phases. Variabl e property effects tire included, as well as the interfacial shear Heat and mass transfer results are presented over a wide range of inlet air concent rations. The average mass fluxes showed a continuous reduction with tin inc rease in the amount of air for a concentration of air as high as 40 percent by weight. But the local mass fluxes showed a different behavior from the absorption of a pure vapor case. The decrease was much higher at the entran ce than in a pure vapor case. The numerical results are in good agreement w ith the experimental data available for lithium chloride. The model has pro mise as means of predicting the heat and mass transfer characteristics of f alling film absorber.