Numerical analyses have been performed to estimate the absorption heat and mass transfer coefficients in absorption process of the LiBr aqueous solution and the total heat and mass transfer rates in a vertical tube absorber which is coolING ed by air. Axisymmetric cylindrical coordinate system was adopted to model the circular tube and the transport equations were solved by the finite volume method. Absorption behaviors of heat and mass transfer were analyzed through falling film of the LiBr aqueous solution contacted by water vapor in tube. Effects of film Reynolds number on heat and mass transfer coefficients have been also investigated. Especially, effects of tube diameter have been considered to observe the total heat and mass transfer rates through falling film along the tube. Based on the analysis it has been found that the total mass transfer rate increases rapidly in a region with low film Reynolds number(10 ~ 40) as the film Reynolds number increases, while decreases beyond that region. The total heat and mass transfer rates increase with increasing the tube diameter.