Double-diffusive natural convection in a trapezoidal solar pond with discrete heat boundary conditions: Effects on non-convective zones

Abstract

A three-dimensional numerical study is conducted to investigate the double-diffusive natural convection inside a trapezoidal solar pond filled with water and salt solution and subjected to discrete heat boundary conditions. It investigates the effect of stored thermal extraction on the non-convective zone (NCZ) of the solar pond. The heat extraction from the middle region on the lower convective zone (LCZ) is modeled as a discrete thermal boundary condition in the NCZ-LCZ. The governing equations are developed using the three-dimensional potential-vorticity formulation and solved using the finite volume method. The numerical computations are performed for the following parameter ranges: Rayleigh number 10³ ≤ Ra ≤ 10⁵ and buoyancy ratio－10≤ N ≤0. Two different cases related to the thermal boundary conditions are investigated. The most important results that are drawn from this study are: (i) the non-uniform heat extraction from the LCZ increased due to vortex formation which disturbed the structure of the flow, and (ii) the three-dimensional effects become more pronounced that caused a decrease in the efficiency of the solar pond. Therefore, when extracting the stored heat from the LCZ layer, it is imperative to maintain the surface temperature as constant as possible and to avoid getting discrete heat surfaces.