Conceptual Design of a Downward-Convecting Solar Pond Filled With a Water-Saturated, Porous Medium

Abstract

Previous results from a stability analysis of natural convection in a water-saturated porous medium with externally imposed downward flow of the fluid and distributed internal heat generation are used in this study for a preliminary design of a saltless solar pond. The pond is filled with a water-saturated porous medium to inhibit natural convection. Downward flow of water is steadily imposed to allow the absorbed solar radiation, dependent upon the extinction coefficient of the water-saturated porous medium, to be carried down to the bottom of the solar pond from whence warm water is conveyed to the point of use. The downward velocities used have small magnitudes to allow useful bottom temperatures to be obtained. A steady-state analytical study was performed to determine the maximum temperature that can be obtained at the bottom of the saltless solar pond which resulted in a relationship involving the internal and external Rayleigh numbers, extinction coefficient, and Peclet number of the imposed downward flow. Results from this analytical study are combined with results from the stability analysis in a design procedure. This procedure is used to design a saltless solar pond of the concept described above for several cases.