Hydrodynamic aspect of hydrothermal synthesis of quartz bulk flow regimes

Abstract
In crystal growth autoclaves, dissolution zone and cristallisation zone are connected through a diaphragm. The flow regimes in such a configuration are quite complex, as they result from two buoyancy mechanisms, solutal and thermal, acting in opposite directions. In addition, the autoclave walls are thick and heat transfer in it strongly affect heat transfer in the bulk (conjugate problem). Several model with increasing difficulties have been numerically tested to calculate the bulk flow. For a thermal boundary condition with a flux imposed at the external wall, the temperature distribution along the internal wall is found to be almost linear. For "thermosiphon" configuration, the axisymmetric solution is completely different, but still the flow goes up along the internal wall inside the two zones. For three-dimensional solutions, the flow is going up along the axis in the crystallisation zone ; showing that the axisymmetric solution is not realistic. In addition, the stability theory indicates that after a certain threshold, the solution would become anti-symmetric and thus will be three-dimensional too.