Freezing of aqueous sodium chloride solution saturated packed bed from a vertical wall of a rectangular cavity

Abstract

Freezing of an aqueous sodium chloride (H 2O-NaCl) solution saturating a packed bed of glass spheres is investigated experimentally. Experiments are conducted on the hypoeutectic side, and the cold wall temperature is lower than the eutectic point. Spherical soda-lime glass beads 2.85 mm and 6 mm in average diameter constituted the packed bed. The effects of initial salt concentration, superheat and bead diameter are investigated. Three distinct regions came into existence during the freezing process. Supercooling was observed only at early times of the freezing process for an experiment with 5% initial salt concentration. However, small supercooling was observed throughout the freezing process for the 15% initial salt concentration experiment. Reheating of the mixture was intensified with an increase in the bead diameter, initial salt concentration, and near the vertical hot wall. At the end of the freezing process, remelting was observed only at the mush-liquid interface for the 10–15% initial salt concentration experiments. Flow visualization experiment and mush-liquid interface observations revealed natural convection in the upper part of the liquid region. An enriched and stratified fluid layer existed in the bottom of the liquid region. The intensity of natural convection was affected by both the Darcy and modified Rayleigh numbers.