EFFECTS OF A NONABSORBABLE GAS ON INTERFACIAL HEAT AND MASS-TRANSFER FOR THE ENTRANCE REGION OF A FALLING FILM ABSORBER

An analytical solution is presented for the effect of air (nonabsorbab le gas) on the heat and mass transfer rates during the absorption of w ater vapor (absorbate) by a falling laminar film of aqueous lithium br omide (absorbent), an important process in a proposed open-cycle solar absorption cooling system. The analysis was restricted to the entranc e region where an analytical solution is possible. The model consists of a falling film of aqueous lithium bromide flowing down a vertical w all which is kept at uniform temperature. The liquid film is in contac t with a gas consisting of a mixture of water vapor and air. The gas p hase is moving under the influence of the drag from the falling liquid film. The governing equations are written with a set of interfacial a nd boundary conditions and solved analytically for the two phases. Hea t and mass transfer results are presented for a range of uniform inlet air concentrations. It was found that the concentration of the nonabs orbable gas increases sharply at the liquid-gas interface. The absorpt ion of the absorbate in the entrance region showed a continuous reduct ion with an increase in the amount of air.