Numerical Simulation On Thermocapillary Convection During Crystal Growth With Liquid Encapsulation

Czochralski method is widely used in producing crystals. The thermocapillary convection induced by interface tension gradient becomes a prominent factor influencing the quality of materials under microgravity condition. The liquid encapsulation Czochralski (LEC) technology of crystal growth plays a very important role in reducing thermocapillary convection. The physical model of two immiscible liquid encapsulation technology is researched in this paper. The results obtained are directly used to crystal growth procedure in the production of pure and high quality crystals.The physical and mathematical models of thermocapillary convection in two immiscible liquid layers are established. The distributions of temperature and velocity in liquid layers are then obtained and effects of a series of non-dimensional parameters on the thermocapillary convection are analyzed. It is verified that liquid encapsulation can reduce thermocapillary convection in the LEC, and the flow profile of two liquid layers is much more complex than that of single liquid layer.In results, under microgravity condition, when the thickness of liquid encapsulation decreases, thermocapillary convection of the fluid in the up and down layers becomes weaker. The augmentation of kinetic viscosity ratio ?* of the liquid encapsulation to molten liquid makes thermocapillary convection of molten liquid be weaken a lot, and it is found that kinetic viscosity has an extremely remarkable effect on the flow profile. For ??<0, the nonlinear distribution of temperature and flow strength become much stronger along with the increase of the absolute of ratio ???of the temperature coefficient of free interface tension to liquid-liquid interface tension. The thermocapillary convection in the down liquid layer appears to get weaker along with the augmentation of Pr. When Ma increases, thermocapillary convection in the two liquid layers gets stronger.The thermocapillary convection in molten liquid can be much more weakened by selecting proper liquid encapsulation with reasonable physical parameters. In earthgravity environment, Gr>104, it is impossible to neglect the impact of buoyancy convection on flow and heat transfer. The convection in molten liquid can be much more weakened by buoyancy convection increasing the flow of liquid encapsulation in this model.