Simulation of Phase Change and Convective Heat Transfer in Float Zone Processing

A computational capability has been developed to predict the free surface shape, heat transfer and melt-crystal interface shapes in float zone processing. A moving boundary, second order, finite volume, incompressible Navier-Stokes solver has been developed for the fluid flow and heat transfer calculations. The salient features of the approach include solving the dynamic form of the Young-Laplace equation for the free surface shape, dynamic remeshing to fit the free boundary, a flexible, multi-block, grid generation procedure and the enthalpy method to capture the melt-crystal and the melt-feed interfaces without the need for explicit interface tracking. Important convective heat transfer modes; natural convection and thermocapillary convection have been computed. It is shown that, whereas the overall heat transfer is not substantially affected by convection, the melt-crystal interface shape acquires significant distortion due to the redistribution of the temperature field by the thermocapillary and buoyancy-induced convective mechanisms. It is also demonstrated that the interaction of natural and thermocapillary convection can reduce the melt-crystal interface distortion if they act in opposing directions.