Lateral freezing of an anisotropic porous medium saturated with an aqueous salt solution

Abstract

Lateral freezing of a porous medium saturated with an aqueous salt solution was investigated experimentally and theoretically to obtain the improved understanding of the solute redistribution during solid/liquid phase change. The emphasis was on the interaction between hydrodynamics and transport of energy and species in the solidifying and unsolidified regions and on the effect of the flow characteristics possessed by the porous matrix and dendrite arrays. Freezing experiments were performed in a square cross-section enclosure chilled and heated from the side by imposing uniform but different temperatures, and filled with the artificial porous structure. The latticed structure of the porous matrix phase and the shadowgraph enabled the flow visualization and the observation of the solidus and liquidus positions. Simultaneous measurements of local temperature and liquid composition at selected locations were also made. An analytical model based on heat and species conservation and relations from the phase diagram is suggested, and the predictions are compared with experimental data. The effect of porous matrix permeability was examined over a wide range of parameters by performing numerical experiments. The porous matrix phase affected the freezing of an aqueous salt solution by offering an additional resistance to the motion of the fluid and migration of separated crystals. The amount of macrosegregation was found to be mainly controlled by the porous matrix permeability in the direction of gravity. Macrosegregation was decreased when the permeabilities of the porous matrix phase and/or dendrite arrays were decreased.