A 2-RAYLEIGH-NUMBER MODEL OF BUOYANCY-DRIVEN CONVECTION IN VERTICAL MELT GROWTH CONFIGURATIONS

This paper presents both experimental and numerical results for thermal buoyancy-driven convection in a model that can be extrapolated to various vertical melt crystal growth configurations if additional convective effects induced by rotation or gradients of the surface tension can be neglected. The model consists of a vertical cylinder with the top, bottom and side walls forming three independent, isothermal boundaries. The hydrodynamic state in this model is described by four dimensionless groups: the aspect ratio (height/diameter), the Prandtl number Pr, the vertical Rayleigh number Ra and a wall Rayleigh number Ra//w. Flow patterns as well as transitions from steady to unsteady convection were studied experimentally for Pr equals 6. 7 (H//2O) and an aspect ratio of 1 for a large range of combinations of Ra and Ra//w. Good agreement was obtained with results of three-dimensional numerical calculations.