The absorption of water vapour in aqueous solutions of lithium bromide is modelled for a falling-film, vertical-tube absorber. The model is based on the solution of three ordinary differential equations to calculate axial solution concentration and temperature distributions and coolant temperature distribution. The heat and mass transfer coefficients employed in the equations are extracted from the literature, incorporating recent information on wavy-laminar flows. Under certain conditions, the numerical solution exhibits instabilities in the entrance region of the absorber tube, which are corrected by the introduction of a dampening factor incorporating relevant thermophysical properties. The usefulness of the model for generating absorber performance charts is demonstrated.

KEYWORDS: Models, computers, calculating, designing, lithium bromide, vertical, tubes, absorbers, performance.