A numerical study of heat transfer and fluid flow in a hydrothermal autoclave with a single- or multi-hole baffle

Hydrothermal solution growth is an important technique to grow high quality piezoelectric single crystals. In industry hydrothermal crystal growth, an autoclave is divided into two chambers by a baffle located in the middle height. Industrial practice found that better quality crystals could be grown under certain baffle hole openings or using a multi-hole baffle. This paper presents a numerical study of the effects of the baffle opening, as well as the arrangement of holes on the baffle, on the fluid flow and temperature fields in an industry-size autoclave. A wide range of baffle hole openings from 2% to 25%, together with five hole-arrangements, is investigated. Computational results indicate that changing the baffle hole opening and number of holes on the baffle are effective ways to control the temperature uniformity in the upper growing chamber. With a single-hole baffle, a smaller hole-opening leads to a weaker flow field and more uniform temperature in the growing chamber. With the same opening area, a multi-hole baffle will perform better than a single-hole baffle. The number of holes in a multi-hole baffle shows a strong effect on thermal condition in the upper chamber with 8-hole baffles working better than both baffles with 4 and 16 holes. The hole-arrangement, however, does have significant effect on thermal condition in the growing chamber.