Single- and multi-hole baffles—a heat transfer and fluid flow control for hydrothermal growth

Abstract

Hydrothermal solution growth is an important technique to grow high-quality single crystals. An autoclave, a closed cylindrical low-carbon steel vessel, is used to grow the large size crystals. A baffle located at the median height divides an autoclave into two chambers. Previous numerical studies indicate that the buoyancy-driven flow within an autoclave is very sensitive to the temperatures on the wall established by the heating. Baffles are required to establish the conditions for growth of high quality single crystals. This paper presents a numerical study of the effects of various baffles on the fluid flow and temperature fields in an industry-size autoclave. A wide range of baffle area openings for a single-hole baffle from 2 to 25%, together with five multi-hole baffles, is investigated. Computational results indicate that changing the baffle hole opening and the number of holes on a baffle are effective ways to control the temperature uniformity in the growing chamber. With a single-hole baffle, a smaller opening leads to a weaker flow field and a more uniform temperature profile. A multi-hole baffle establishes a more uniform temperature in the upper chamber than a single-hole baffle of the same area opening. The number of holes of a multi-hole baffle shows significant effects while the hole arrangements, however, affect the thermal condition only in the near-baffle region.