PIV Study on Double-Diffusive Convection during the Unidirectional Solidification of a Hypereutectic Binary Solution

The solidification of a binary solution occurs in a variety of industrial applications. The fundamental mechanism of the development of "double-diffusive convection" during solidification was one of the main subjects of study in the past. This study focused on the effect of the initial concentration of an aqueous ammonium chloride solution on the development of double-diffusive convection during the solidification process. ne particle image velocimetry (PIV) technique was employed to measure the flow velocity and observe the morphological conditions associated with the unidirectional solidification (UDS) from below. In addition, the temperature distribution and the growth rates of mushy and solid zones within a test cell were measured by using the designed experimental system. The experimental results revealed that a hypereutectic binary solution with higher initial concentration generated stronger double-diffusive convection, causing the liquid with lower temperature to be transported to the top of the test cell. The channel flows that caused "freckling" during UDS were disclosed in the PIV measurement for the binary solution with high concentration. Moreover, with an increase in the initial concentration of the binary solution, the growth rate of the mushy zone increased, while that of the solid zone was unaffected. The nonequilibrium phenomena that caused the deviation of the liquidus front from the measured liquid/mush interface were also discussed in this study.