A simplified mathematical model of glass melt convection in a cold crucible induction melter

摘要

Cold crucible induction melting is emerging as a promising technology for immobilizing nuclear waste in glass matrices. Since the transport properties such as viscosity and electrical conductivity of molten glass exhibit strong temperature dependencies, performance of the cold crucible induction melter is highly sensitive to the thermal field prevailing in the molten glass pool. A simplified mathematical model was developed to numerically investigate the impact of molten glass properties such as viscosity, thermal conductivity and electrical conductivity on the performance of a cold crucible induction melter meant for high level radioactive waste vitrification. The present investigation of the thermal convection using the simplified model confirms the findings of previous studies. Numerical simulation of thermal convection shows that low electrical conductivity and high viscosity existing in the cooler parts of the molten glass bath can lead to poor electromagnetic induction and localized heating in the present melter-inductor configuration. The stable thermal stratification due to bottom cooling leads to a relatively stagnant fluid layer in the lower part of the glass melt. These features of the thermal convection can limit the heat transfer and mixing in the glass melt which in turn can affect both the melting capacity and product homogeneity adversely. Mechanical stirring using a water-cooled stirrer can overcome these limitations. The present study confirms that mechanical stirring of the glass melt can enhance the electromagnetic induction through thermal homogenization. Mechanical mixing eliminates the relatively stagnant fluid layer observed in thermal convection. Distribution of induced power, temperature and velocity predicted by the simplified model exhibit matching characteristics of the results obtained by other investigators. The simplified model reduces the computational load substantially as it eliminates complex electromagnetic computations.