Effect of operating conditions such as feed temperature, feed circulation rate and feed inlet concentration on permeate flux in a direct contact membrane distillation (DCMD) have been simulated. The effects of these parameters on both temperature and concentration polarizations have also been taken into account. A simultaneous heat and mass transfer model has been used in the DCMD system. The model has been solved numerically using MATLAB. Significances of the heat transfer due to mass flux, heat lost by conduction, as well as their contribution to the overall heat flux through the membrane have been determined. The variation of physical and flow properties with temperature and consequently heat transfer coefficients have been considered in this study. The influence of mass transfer on heat transfer coefficients and heat transfer rates has been considered in heat transfer equations. Finally, the simultaneously effects of the operating parameters on response variables have been studied. (c) 2012 Elsevier B.V. All rights reserved.