A crucible cover is designed in a furnace for growing sapphire crystals by heat exchanger method. Global simulations of heat transfer are carried out to investigate its effects on the thermal held and melt flow in the crucible during the growth of sapphire crystal, It is found that the crucible cover has significant effect on the thermal field in the melt. When the crucible cover is installed, the radial temperature gradient in the melt at the melt-crystal interface decreases while the axial temperature gradient increases. The melt flow is weakened accordingly. The melt-crystal interface becomes Hatter and the thermal stress in the crystal is reduced with the installed crucible cover, It can be therefore concluded that use of a crucible cover is favorable for crystal growth. (C) 2014 Elsevier B.V. All rights reserved.