Thermal Field Coupled With Fluid Flow Numerical Simulation Of Multi-crystalline Silicon Continuous Casting Process

Multi-crystalline silicon (mc-silicon) which contributes a large portion of the photovoltaic materials is widely used for its significant cost advantage. Casting method for preparation of mc-silicon has been applied for its outstanding low-cost performance including filling method and directional solidification method. However, yield and production efficiency are still quite low in these methods. In order to improve the production efficiency, we conducted a study on the preparation of mc-silicon billet using continuous casting method including numerical simulation and preliminary experiments. By using the software ProCAST, different thermal behaviors between silicon and other metals during continuous casting process was analyzed. According to the special physical property during solidification of silicon, taper of the mold used for silicon continuous casting was carried out combined with contact stress simulation. Based on this, a silicon continuous casting apparatus was designed. Through the comparison with analytical solution and actual measurement results of a texting case, accuracy of thermal filed coupled with fluid flow simulation results of the software was verified. Based on this, the thermal-fluid coupled simulation about the entire mc-silicon continuous casting process was carried out including startup stage and steady stage. To optimize casting recipe and predict billet cooling behaviors during the casting process, a three-dimensional finite element model for the simulation of thermal field and fluid flow was built. The continuous casting of cylindrical silicon billet was studied considering different casting parameters such as withdrawal speed and heat transfer ability of mold. Simulation results indicate that lower casting speed and lower heat transfer coefficient of mold are beneficial to acquire better morphology. Experimental works were practiced lying on the modeling results, using the self-designed mc-silicon continuous casting apparatus, mc-silicon billet with a diameter of 100 mm was obtained.