Gas Blowthrough of a Liquid Metal Bath by an Upward Directed Submerged Jet

A novel instrumentation system has been developed which can measure the fraction of time that a gas jet penetrates from its point of injection to the surface of a liquid metal bath. Such penetration of the bath by injected gas is also termed "blowthrough". Using this new instrument the conditions required for blowthrough have been studied using a liquid tin model of a bath smelting vessel. The experimental results confirm a criterion previously published by Kato et al. for the onset of blowthrough provided the gas injection rate is low. It is shown that the limit of applicability of the Kato criterion corresponds to the onset of compressibility effects in the injected gas. A modification to the Kato criterion is developed which extends its range of applicability into the compressible gas flow regime. Experimental results confirm that the modified Kato criterion correctly predicts the influence of injection nozzle diameter, gas density and gas sonic velocity on the gas flow required to cause blowthrough at a given bath depth.