This paper presents a numerical investigation on a new heating configuration for hydrothermal crystal growth vessels. On the upper growth camber, the top wall is cooled and the sidewall is insulated while the lower chamber is heated on the side wall. The thermal environments in the autoclaves with the top wall cooling and the conventional sidewall-cooling configurations are compared. Results show that the top wall cooling configuration establishes a much better thermal and flow environment in the upper growth chamber. With the sidewall-cooling configuration, the flow consists of a jet-like flow along the vertical centerline and downward wall layers. Comparatively, with the top wall-cooling configuration, the three-dimensional unsteady swirling flow establishes a more homogeneous and isotropic thermal and flow environment in most of the space in the main growth region which is ideal for the crystal growth. In the lower dissolving chamber, which is heated on the sidewall, temperature is higher near the baffle and lower at the bottom. Such a temperature distribution guaranties the raw material on the top of the stack be dissolved first. (c) 2006 Elsevier B.V. All rights reserved.