Gallium nitride (GaN) is a semiconductor material with a wide array of applications in the manufacture of blue/green light LEDs, lasers and high power electronic devices. In the ammonothermal growth, ammonia is used as a solvent instead of water as in the hydrothermal process. We modeled ammonothermal growth of GaN crystal of 1 in. size in a cylindrical high-pressure autoclave and discussed the effects of the different baffle design. We can conclude that, under the condition of forward solubility, the small opening is not in favor of the crystal growth. When the opening increases from 12% to 16%, the flow direction in the central hole changes from positive to negative. In the cases of 16% and 20% openings the flow in the autoclave exhibits a steady circulation, so the growth is stable. The transfer of raw material depends on the baffle opening and the temperature difference between growth zone and dissolving zone. (C) 2010 Elsevier B.V. All rights reserved.