Rapid solidification of subcooled small metallic drops: Internal nucleation

Solidification of subcooled internally nucleated spheres is analyzed including surface energy and initial radius effects. Accurate and simple rapidly and slowly varying solutions are obtained. Large supercooling leads to enormous heat transfer rates during recalescence, comparable to those obtained in splat cooling, when the liquid shell increases very quickly from the nucleation temperature to the melting point. After recalescence, external convective heat transfer dominates and this period begins when the dimensionless thickness of the solidified core region is approximately equal to the cube root of the Stefan number. A simple analytical expression for complete freezing of the droplets is given. Recalescence is complete in microseconds, a small fraction of the total freezing time, which is typically on the order of milliseconds. The Gibbs-Thompson effect is important only at small times, on the order of 10-10 s, but during this period the growth rate is profoundly effected by surface energy effects.