Unsteady thermocline degradation in a fluid-saturated, porous medium

Abstract

A numerical model is developed to describe unsteady, three-dimensional, natural convective flows in a fluid-saturated, porous medium having a rectangular volume with impervious walls and finite heat transfer at the boundaries. The model is used to predict the transient decay of a thermocline in a packed bed during a period of stagnation in which there is zero net flow and no energy input into the bed. The computed results compare favorably with experimental data from a packed bed consisting of air and natural stone of mixed sizes and irregular shapes. The results show an upward shift in the position of maximum temperature along the vertical centerline of the bed and confirm the important influence of internal convection on the process. The results also demonstrate that a purely diffusive model would be incapable of a reliable predication. Further, the recognition of finite heat transfer rates at the boundaries is shown to be a significant factor in improving the predictive capability of the model.