Heat transfer and cristallization kinetics of melted drops under intensive cooling

The process of microscopic melted drops solidification under intensive cooling is investigated. A two stage model of the process is suggested. At the first stage the volumetric mechanism of crystallization including formation of viable nuclei and their further growth is realized. It is shown that because temperature dependencies of the nucleation rate and of the crystal growth rate are nonmonotone the nucleation process near the cooling surface runs more intensively than in remaining volume of a drop. It results in formation of a continuous crystalline layer (in the external area). The consequent stage of frontal crystallization is described by a generalized Stephan problem. The process runs with a supercooling of front and the velocity of front moving is determined by thermal balance and frequency of incorporation of liquid phase atoms to a crystalline layer.