A two - fluid turbulence model is used to develop a two - dimensional theoretical model for predicting the two - phase flow on a sieve tray. Then the influence of the turbulence of the third dimension on the two - dimensional flow pattern is considered by correlating the constants of the model to the height of the overflow weir. Comparison of the computed results with the experiments of the sieve tray shows that the proposed model can successfully simulate the velocity field on the tray.