Double-diffusive convection during solidification of a metal analog system (NH4Cl–H2O) in a differentially heated cavity

This experimental study focused mainly on the solidification of a binary mixture of ammonium chloride and water (NH4Cl–H2O) in a differentially heated cavity. One vertical wall was cooled to temperature TC=−20 °C, and the other opposite vertical wall was kept at a constant temperature TH=+20 °C. The effect of the initial concentration of ammonium chloride on the solidification process was considered. Particle image velocimetry was used in this study for the visualization of the dynamic field during the solidification process. The temperature distribution at discrete locations in the solution and on the vertical cooling wall were monitored using thermocouples. The convection flow patterns, the ice thickness, and the temperature distribution were obtained for various initial concentrations of ammonium chloride ranging from 0 to 20 wt.% (sub-eutectic and near-eutectic growth). The results obtained in the course of this study reveal that (1) the initial concentration plays a significant role in the evolution of convection flow patterns, (2) the thickness of the frozen layer depends on position inside the cavity (top, middle, bottom), (3) the ice growth rate was almost double at the bottom of the cavity, and (4) the process of solidification is slower with an increase in the initial concentration levels of the binary solution.