This paper describes a model of the absorption process in a falling film Lithium Bromide-Water absorber. Absorption of a gas or vapor into a laminar falling film on the surface of a vertical tube is taken into account. Necessary boundary conditions are provided to solve simultaneous parabolic partial-differential equation which are obtained by diffusion and energy equations characterizing absorption process. To solve these partial differential equations Crank-Nichelson Method was used. Solutions for temperature and concentration distributions were obtained by applying these equations in discretized flow field. Nusselt and Sherwood numbers are calculated for absorber. The coolant-side heat transfer coefficient may be calculated using standard correlations. The effect of varying coolant flow rate, solution flow rate and coolant temperature are also studied.