The transient natural convective thermal/fluid processes during discharge of an inclined rectangular solar storage tank via an immersed heat exchanger are modeled and compared to prior experimental data. The model treats the heat exchanger as a porous medium within the storage fluid and is applicable to a wide range of tank/heat exchanger configurations. In the present study, a two-dimensional model is applied to discharge of a 126 1 storage tank inclined at 30 deg with respect to the horizontal and with a height to width ratio of 9:1. The heat exchanger has 240 tubes arranged in parallel and is located near the top of the tank. Transient temperature distributions and flow streamlines demonstrate the complexity of the flow field and the extent of mixing during discharge. The predicted results compare favorably to prior measurements of heat transfer and temperature distribution.