A predictive model is developed to describe heat transfer and fluid dynamic behavior of a helical double-pipe vertical condenser used in an absorption heat transformer integrated to a water purification process. The condenser uses water as working fluid connected in countercurrent. Heat transfer by conduction in the internal tube wall is considered; in addition the change of phase is carried out into the internal tube. The dynamic model considers equations of continuity, momentum and energy in each flow. The discretized governing equations are coupled using an implicit step by step method. Comparison of the numerical simulation over range of experimental data presented in the heat device is applied to validate the model developed. The model is also evaluated of form dynamic to determine the principal operation variables that affect the condenser with the main objective to optimize and control the system. A variation of mass flow rate in the internal pipe induces important changes on the heat flux that the pressure and temperature. (c) 2010 Elsevier Ltd. All rights reserved.