Enhanced thermal stratification in a liquid storage tank with a porous manifold

Experiments were conducted to investigate the effectiveness of a porous manifold in the formation and maintenance of thermal stratification in a liquid storage tank. A thermal storage tank with a capacity of 315 L and a height-to-radius ratio of 4 was used for the experiment. The porous manifold used was made from rolling up a nylon screen into the shape of a tube. Stratification was observed at a Richardson number as low as 0.615. Flow visualization was also performed to confirm the effectiveness of the porous manifold in the promotion and maintenance of stable thermal stratification. From the results of flow visualization, one can conclude that a porous manifold is able to reduce the shear-induced mixing between fluids of different temperature, and thus is able to promote and maintain a stable stratification.

► Porous manifolds are shown to be an effective means in the promotion and maintenance of thermal stratification in a liquid storage tank.
► Porous manifolds are rather inexpensive, which can be made by rolling up a nylon screen into the shape of a tube.
► It has been observed that thermal stratification can be established at a Richardson number as low as 0.615.
► The degree of stratification is shown to be a function of Richardson number and inversed Peclet number.
► The degree of stratification is mainly a function of the Richardson number when the inversed Peclet number is small, but becomes independent of the Richardson number for larger inversed Peclet number.