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2. Background Aconsiderable body of theoretical and experimen-tal work concerning gas injection systems has been undertaken in recent years. In most of these studies, air and water were used to model gas injection in metallurgical processes. 112) Inthese studies it was assumedthat gas penetration is confined in a cylindrical or conical region around the axis of the injection nozzle. Single phase flow equations were solved for the liquid phase with spatially varying density. Thedensity of the mixture wascalculated as a function of the phasevolume fractions. Boundaries of the gas-liquid two-phase plume were determined from experimental observations. To investigate the structure of the two-phase plumeregion, Castillejos and Brimacombel3~ 15) performed experi-mental studies in airwater, nitrogen-mercury and helium-mercury systems. From the results of these studies they suggested correlations for the gas phase volume fraction distribution as a function of fluid properties and system geometry. Realizing the limitation, s of the single phase formula-tion. McKelliget et al., 16) Lai and Salcudean, 17) Salcudean and Lail8) and Lai et a/. i9) used a mathematical model in which Navier-Stokes equations were solvedfor the liquid phase, while a set of simplified conservation equations were solved to predict the gas phase fiow.