A study on the snowing phenomenon in binary alloy solidification

The snowing phenomenon has been observed in some studies where seed crystals formed near the bottom of the test cell during solidification are carried up flow above the mushy layer by thermo-solutal convection flow, and they fall down on it just like atmospheric snow occurring in nature. In this study, snowing phenomenon was studied by varying parameters which could affect the thermal as well as solutal gradients, at six weight % concentrations of ammonium chloride solutions, from 23% to 26%, with temperatures −24 °C, −20 °C and −16 °C, and at volume of solution either full or half-full. Results show that increase in concentration decreases the onset of snowing, does not lengthen the period of the observed phenomenon, but increases the size of ejected crystals. Increase in temperature does not significantly affect the onset of snowing, but lengthens the period of snowing. Similarly, an increase in volume does not affect the onset of snowing but lengthens the process based on the ratio of the volumes. While concentration and temperature affects the final mush profile in the study, different volumes of solution does not. The combined Rayleigh number is calculated but found to produce no conclusive critical Rayleigh number to predict the onset of snowing.

► We observed snowing phenomenon of seed crystals during solidification of binary alloy from a bottom cold surface.
► Snowing phenomenon was investigated at six different concentrations of ammonium chloride solutions, from 23% to 26%.
► Snowing phenomenon was investigated at three different base temperatures of −24 °C, −20 °C and −16 °C.
► Snowing phenomenon was investigated for full volume or half-volume of binary alloy solution in the test cell.
► Results show that increase in concentration decreases the onset of snowing.