Hydrothermal growth is the industrial method of preference to synthesize high-quality single crystals. The growth vessels, called autoclaves, are cylindrical containers filled with solutions of the crystal material. Under normal conditions, the fluid flows are three-dimensional. A baffle is used to partition the container into two chambers. This paper presents a systematic investigation on the transports through the baffle openings. Results indicate that a single-hole baffle is effective in controlling the fluid exchange and heat transfer between the two chambers. A smaller baffle opening establishes more uniform temperatures in the chambers. The flow structure shows that there is a pair of flow streams across the baffle opening. However, the heat exchange carried by this pair of streams, as well as heat exchange through molecular diffusion, is small. The transport through baffle opening is dominated by turbulence diffusion. Further heat transfer analysis shows that the characteristic length scale in industry growth vessels is a combination of the diameter of the baffle opening, the diameter of the autoclave, and the height of the chambers.