Analytical investigation of a combined heat and mass transfer process in a counter-current ammonia water based absorber is presented. The model accounts for both liquid and vapor phase mass transfer resistances, and uses empirical correlations to predict the heat and mass transfer coefficients. The model was used to analyze a lamella, plate based absorber with falling film absorption. A finite difference technique was employed to solve the numerical model. It was found that the major portion of the mass transfer resistance lies primarily in the liquid phase. A parametric analysis was also conducted to assess the effect of various parameters on the performance of the absorber. (C) 2004 Elsevier Ltd. All rights reserved.