A numerical model for a porous manifold has been developed to study its effects on thermal stratification in a typical storage tank. The tank considered has a capacity of 300 1 and a height-to-diameter ratio of 2. The numerical model employs a transient stream function-vorticity formulation to predict the development of flow and temperature fields in a charging process. The Reynolds number of the inlet flow is fixed at 200 and a wide range of the Richardson number (0.01 less than or equal to Ri less than or equal to 100) is considered. Other parameters considered include the Biot number (i.e. heat loss from the tank), the Darcy number (permeability of the porous manifold), the location of baffle, and the thickness of the porous tube. The results show that all these factors should be taken into account for a better design of a thermal storage tank. In addition, the results provide an envelope for these design parameters.