Numerical Simulation And Optimization Of Directional Solidification Heat Transfer In Polycrystalline Silicon

Due to difficulties in experimental testing, numerical simulation is a very useful tool to study the directional solidification process. In this paper, numerical simulation was carried out to investigate the temperature distribution, melt convection and melt/crystal interface and the impurity distribution to predict. And thus the quality of the final production of silicon ingots can be predicted and the process improvements and optimization design of furnace can be obtained by providing theoretical guidance.A transient global simulation was carried out to investigate the effect of pulling-down rate on in vacuum directional solidification purification process for SoG-Si in metallurgical route. Simulation results show that the m-c interface is less convex to the crystal and its variation is smaller for10μm/s, it further contributes to desirable crystal growth. We found that silicon ingots produced by vacuum directional solidification purification with pulling-down rate of10μm/s can meet the crystal morphology requirement of solar grade silicon (SoG-Si). So we proposed a new route for metallurgical production of solar wafers which combining with removal of impurities and ingot casting process into a process. The effect of silicon nitride (Si3N4) crucible compared with silica crucible and the susceptor (with or without graphite susceptor) on purification in vacuum directional solidification process is also studied. As a result of greater melt flow intensity, higher gas/melt interface temperature, slower solidification rate and slightly convex solid/melt interface shape, silicon vacuum directional solidification purification process using Si3N4crucible without susceptor will have a better purifying effect. A geometry modification has been made on laboratory multi-crystalline directional solidification furnace in order to save energy by a cylindrical solid block added on lower corner of insulations. We performed a transient simulation to investigate the effect of modification on the thermal field. We found that the total energy consumption, convection heat loss and radiation heat loss decreases for optimized furnace.a new model established for flow, heat and mass transfer coupling, which including the process of segregation and vacuum volatile of impurities.we calculated the distribution of impurities Al. But the large difference between the simulation and experimental results, which need to further modified.