Double Diffusive Natural Convection in Crystal Growth

点击翻译按钮获取中文摘要

In the process of crystal growing of pure materials, very small amount of impurities are accumulated just outside of the solidification front. This induces the concentration gradient an concentration natural convection. The cooling temperature gradient and concentration gradient induce so to speak double diffusive natural convection.This is the theme of the present research. At the beginning, two phase layrs were adopted as a most simple system of double diffusion. The lower half layr is a dense salt water layr and the upper half layr a pure water layr. Both layrs are heated from the one vertical side and cooled from opposing vertical side. After two layrs are strted to be heated and cooled, salt component is continuously diffused to the upper layr and the salt-thick plume is raised upward along the heated wall. Because of the high Lewis number of the system, the thick concentration boundary layr is kept for long and the core regime is relatively pure water for many hours. This induces oscillatory convection both in the upper and lower layrs. The temperature dependence of the properties were found to move the two-layr interface constantly upward. The mass transfer rate was correlated by a single equation. It is determined not by the concentration differece but by the diffusion coefficient. Various systems for the buoyant forces due to temperature and concentration either opposite or the same directions were studied for the oscillatory convection characterstics.