Multiphase Mass Transfer Gas Blowing Model for Wave-Enhanced Boron Removal from Molten Silicon

As the world transitions further towards green energy, the demand for high-purity silicon is increasing due to the importance of photovoltaics in the market—one of the industrial steps to obtain solar grade silicon can be gas blowing refinement, which removes unwanted impurities from silicon, including boron. However, to keep up with global demand, production costs must be driven down. This paper describes a novel numerical gas blowing refinement model, implemented with a custom OpenFOAM solver, which investigates the possibility of increasing the efficiency of the gas blowing refinement process by introducing surface waves on the silicon melt. The model is a two-phase, multi-species model which includes species mass transfer at the melt–gas interface, as well as interfacial chemical reactions. The model is initially verified with experimental results, then used to investigate the impact of surface waves on boron removal during gas blowing. The results indicate that introducing waves on the silicon melt surface can significantly improve boron mass transfer from the melt to the gas. Wave amplitude and wave steepness are singled out as important factors that determine how beneficial the waves are to mass transfer. Specific mechanisms why these factors impact boron mass transfer are discussed.