Modeling mean flow and turbulence characteristics in gas-agitated bath with top layer
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INTRODUCTION
RECENT advances in computational methods have generated considerable interest in the mathematical representation of flow phenomena in gas-agitated systems. Such phenomena are relevant in the clean-melt treatment of steel in ladle metallurgical operations, various direct iron and steelmaking operations that are currently being implemented in industry, and the secondary refining of aluminum and copper. This method of agitation has two major advantages. First, by injecting the gas at high pressure through molten steel, a recirculating current is generated, which serves to mix the steel and homogenize the temperature. Second, through careful choice of the dispersed phase, a chemical reaction may be promoted with the impurities in the native steel, thereby enhancing their flotation to the surface to form a slag. A major problem with this method of fluid mixing and impurity removal is the re-entrainment of the slag into the molten steel. This phenomenon, which is generally associated with the mixing and flow characteristics at the slag/metal interface, has attracted the interest of many researchers in recent years.[1–8] Although the mechanism of slag entrainment is well understood, relatively little is known about the effect of such entrainment and the slag layer on flow characteristics of gas-agitated systems. Such a problem is addressed in this article through numerical study of a water system agitated by bottom-blown air and a critical comparison with the experimental data for two distinct water systems of different overlying fluid layers. OLUSEGUN J. ILEGBUSI, Associate Professor, is with the Department of Mechanical, Industrial and Manufacturing Engineering, Northeastern University, Boston, MA 02115. MANABU IGUCHI, Professor, is with the Division of Materials Science and Engineering, Hokkaiddo University, Sapporo, 060 Japan. KEIJI NAKAJIMA, Research Scientist, is with Sumitomo Metal Industries Ltd., Hyogo, 660 Japan. MITSUHIRO SANO and MITSURU SAKAMOTO are Graduate Students with the Graduate School, Osaka University, Osaka, 565 Japan. Manuscript submitted November 1, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
The mechanism for initiation of slag entrainment into molten steel has been investigated by several researchers.[1– 8] Iguchi et al.[9] used water-model experiments to establish an empirical correlation between the critical conditions and the gas flow rate, geometry of the vessel, and physical properties of the slag and metal. While this correlation has been validated for a few nonisothermal systems, its applicability to real steelmaking systems has not been established. Lin and Guthrie[10] investigated the effect of density ratio between the two layers on the emulsification of the top layer. This work has demonstrated that emulsification is dominated by the entrainment of the lower (denser) layer into the upper layer at large density ratios, while inverse emulsion of top layer droplets occurs in the lower layer at small density ratios. The experimental measurement of Nakajima et al.[11]
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