A numerical model has been developed to study the effects of a porous manifold on thermal stratification in a storage tank. The model is used to predict the development of flow and temperature fields during a charging process. Computations have covered a wide range of the Grashof number (1.8 × 10 5 < Gr < 1.8 × 10 8 ) and Reynolds number (10 ≤ Re ≤ 10 4 ), or in terms of the Richardson number, 0.1 < Ri < 10 5 . The results obtained compare favorably well with the experimental data. In addition, the present results have confirmed the effectiveness of porous manifold in the promotion of thermal stratification and provide useful information for the design of such system.