Effects of argon flow on heat transfer in a directional solidification process for silicon solar cells

A global heat transfer model, including the melt convection, argon flow, thermal conduction, thermal radiation and fully coupled boundary conditions, was developed to investigate the argon flow effect on the temperature distribution and melt convection in a directional solidification furnace for silicon solar cells. Both the effect of argon flow rate and the effect of furnace pressure were examined. It was found that the heat transfer at the melt free surface due to the gas convection cannot be neglected, though the argon flow contributes little to the global heat transfer at most radiative surfaces. The shear stress caused by the argon flow at the melt free surface becomes larger with the increase in argon flow rate and it further changes the velocity and temperature distributions in the silicon melt. We also found that the effect of argon flow on the melt convection at a low furnace pressure will be enhanced if the argon mass flow rate is kept constant. The solidification process can thus be controlled by modifying the argon flow rate and the furnace pressure.