Numerical modelling of the flow and concentration polarization in pressure driven membrane process is challenged by the complex coupling in the flow, mass and energy equations along with any added effects of variable solution properties. The present study is directed towards the establishment of a numerical method capable of predicting the flow and concentration characteristics of the laminar channel flows with permeable wall taking into account the variable properties of the stream. The present results highlights the necessity of the fine mesh grid near the membrane wall to cope with the very steep changes in concentration and temperature there and to the importance of making the permeation velocity vary with concentration. The model was validated and the results showed a good agreement with the previous numerical and experimental results.