Numerical study of heat transport and fluid flow of melt and gas during the seeding process of sapphire Czochralski crystal growth

For the seeding process of the Czochralski crystal growth of sapphire, the flow and temperature field with a nonflat melt-gas interface have been studied numerically using the finite element method. The configuration usually used initially in a real Czochralski crystal growth process consists of a crucible, active afterheater, induction coil with two parts, insulation, melt, and gas. At first, the electromagnetic field produced by the radio frequency (RF) coil in the whole system and the volumetric distribution of heat inside the metal crucible and afterheater were calculated. Using this heat distribution as a source, the fluid flow and temperature field were determined in the whole system. We have considered two cases: (1) configuration without a gap between crucible and afterheater and (2) with a gap, corresponding to an often used growth situation in our lab. It was shown that an active afterheater and its location with respect to the crucible influences markedly the temperature and flow field of the gas in the chamber and partly also in the melt.