Effect of Crucible Location on Heat Transfer in Sapphire Crystal Growth by Heat Exchanger Method

A global model of heat transfer, including melt convection, solid conduction, surface radiation, and crystal internal radiation, as well as phase change, is established for a sapphire crystal growing system by a heat exchanger method. Global simulations are carried out to investigate the effects of crucible location on heat transfer and sapphire crystal growth in the growing system. It is found that the crucible location has a significant effect on the heat transfer in the crystal and melt domains. When the crucible rises up, the melt flow is enhanced and the convexity of the melt-crystal interface increases at the crystallization stage. The thermal stress in the growing crystal decreases at the annealing stage. It therefore can be concluded that the crucible should be lowered at the crystallization stage, and raised up at the annealing stage, to obtain high-quality sapphire crystals.