Freezing of Water-Saturated Porous Media in the Presence of Natural Convection: Experiments and Analysis

Freezing of superheated water-porous media (glass beads) contained in a rectangular test cell has been studied both experimentally and numerically. The effects of liquid superheat and imposed temperature difference were investigated. When the superheat across the liquid region was small the flow in the porous media was weak, and the interface was almost planar. For larger superheats, natural convection flow and the solidification front shape and velocity were found to depend on the imposed temperature and the permeability of the porous medium. Due to the density inversion of water, the rate of freezing was higher, either at the top or at the bottom of the cell, depending on the amount of superheat. The measured temperature distributions were compared with predictions of numerical model that considered both conduction in the solid and natural convection in the liquid region. This model is based on volumetric averaging of the macroscopic transport equations, with phase change assumed to occur volumetrically over a small temperature range. Both Brinkman and Forchheimer extensions were added to the Darcy equations. The effect of density inversion of water on the fluid flow and heat transfer has been modeled. Good agreement has been found between the experimental data and numerical predictions.