Heat transfer, fluid flow, and transport control during hydrothermal growth of quartz single crystals.

摘要

Hydrothermal growth is currently the industrial method of preference of obtaining high quality piezoelectric single crystals. In order to obtain high quality single crystals, industry hydrothermal growth is normally a surface kinetics dominated process. However, the growth rate and quality depends on the temperature, which in turn is determined by the buoyancy force driven fluid flow. On the other hand, flow and heat transfer process in industry hydrothermal autoclaves are not well understood to date.; The focus of this study is on the heat transfer and fluid flow in industry hydrothermal autoclaves and the transport control methods to improving the growth environments. Published works in literature related to this topic and flow studies with similar configurations are intensively reviewed. Heat and mass transfer and growth mechanism are analyzed. Based on the previous efforts, numerical models are first developed. Second, the numerical models are experimentally validated. Third, simulation runs are carried out for the flow and heat transfer in industry scale autoclaves. Finally flow control methods are developed.; Results show that an axially symmetric flow is established when the thermal (heating) condition of an autoclave is axially symmetric. The axially symmetric flow is ideal to growth with large flow and temperature variations in the near baffle region and the rest of the growing chamber enjoys a uniform temperature and low strength flow. Larger space with uniform growth environment can be obtained by using higher aspect ratios. The axially symmetric flow, very sensitive to the asymmetric factors, can be broken and switched to an asymmetric one-cell pattern by a small asymmetric factor. In most of the industry autoclaves, flow is three dimensional. The conjugate model shows that small asymmetric heating on the wall outside surface can cause a small temperature deviation, which is still large enough to change the flow pattern.; Finally based on the understandings of the flow and the heat transfer process, flow and transport control methods are proposed and developed. An inverse algorithm is developed. It is shown that baffles and the outside heating are effective for transport control methods for industry autoclaves.