The impact of periodic forced convection on the double-diffusive convection of a liquid binary alloy during the unidirectional solidification process

In the past, one of the main issues for the solidification of a liquid binary alloy focused on how to eliminate or weaken the "double-diffusive convection" because it is the main reason to cause the poor quality of alloys. To find a method to remove or reduce the double-diffusive convection, the objective of this study is to investigate the effect of periodic lid-driven flow on the development of double-diffusive convection during solidification. A hypereutectic aqueous ammonium chloride (NH₄Cl-H₂O) solution was adopted as the test sample and it was put into an enclosure cooled from the bottom, known as unidirectional solidification (UDS) process, to investigate the heat and mass transport phenomena during solidification. The measurement of the flow visualization by shadowgraph technique, movement of liquid-mush interfaces, temperature distribution and concentration distribution were conducted during solidification. Experimental results revealed that with increasing the speed of periodic lid-driven flow, the double-diffusive convection became weak, the plume appeared rather late and the time of developing double-diffusive convection became short. For periodic lid-driven velocity with 5.3 cm/s, the number of the channels was reduced by 60% as compared to that of UDS without externally imposed periodic lid-driven flow.