We carried out global simulations of heat transfer to investigate the argon flow effect on the melt convection and melt-crystal (m-c) interface shape at different stages of an industrial directional solidification (DS) process for the multi-crystalline silicon (me-Si) ingot. We found that the convective heat transfer at the melt free surface due to the argon flow significantly changed the temperature distribution in the upper layer of the silicon melt. The shear stress caused by the argon flow along the melt free surface increases with an increase in argon flow rate. The melt flow pattern under the central area of the free surface changes accordingly. The argon flow has little impact on the m-c interface shape at the early stage of the DS process. At the middle stage, the m-c interface shape is mainly influenced by the pattern and intensity of the melt convection, which are modified by the argon flow. It is less convex to the melt with a larger argon flow rate. However, the m-c interface is more convex to the melt with an increase in argon flow rate at the final stage of the DS process, because it is then directly affected by the cooling effect of the gas flow. (C) 2011 Elsevier B.V. All rights reserved.