Buoyancy driven heat and species transports inside an energy storage enclosure partially saturated with thermal generating porous layers

Abstract

Combined thermal and moisture convections in an enclosure partially filled with porous medium are numerically and analytically investigated, aiming to enhance moisture transport in the thermal energy storage unit. Two representative configurations of porous layers were taken into considerations, being placed centrally in the space or attached to the vertical walls. Moist air motions are simultaneously driven by the internal heat generation and external concentration difference imposed across the enclosure. Effects of Darcy number, mass diffusion coefficient, thermal Rayleigh number and buoyancy ratio on the heat and moisture transfer across the enclosure are discussed. Heat and mass transfer of the fluid/porous interface is analyzed as a function of the permeability of the porous layer. In the extreme case of high permeability and solutal-driven flow, a scale analysis is applied to predict the order of magnitudes involved in the boundary layer regime. Also, correlations for the average Nusselt and Sherwood numbers based on discrete numerical results are proposed. There is an agreement between the analytical and numerical results of moisture transfer rate, while a slight difference of heat transfer rate is observed due to different configurations of porous layers were imposed. Present research could benefit future development of sustainable building energy storage.