Physical and Mathematical Modeling of Inert Gas-Shrouded Ladle Nozzles and Their Role on Slag Behavior and Fluid Flow Pa
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THE injection of argon gas into the ladle shroud and submerged entry nozzles (SENs) is a common practice in continuous casting to prevent the melt stream from reoxidation by the aspiration of ambient air. The benefits that result from shrouding the melt stream are manifold. The oxygen content in the bath experienced a definite reduction, a lesser number of oxide inclusions, a decrease in nozzle-clogging frequency, an improvement in the surface quality of slabs and billets, as well as a reduction of melt temperature loss from ladle to tundish.[1] Despite these benefits, argon gas should be avoided, because it forms an exposed eye of steel around the ladle shroud by sweeping off the protective layer of tundish slag. The optimal argon flow rate depends on casting speed, tundish level, and nozzle bore diameter.[2] G.M. Evans et al.[3] determined that for applications like SENs, too much gas injection results in a transition from the bubbly flow regime to the churn-turbulent regime, which is not desired. Thus, it is essential to have a scientific understanding of the gas-shrouding phenomenon to make it easier to optimize the process. Bai and Thomas[4,5] studied the turbulent flow of liquid steel and argon gas bubbles in a slide-gate tundish nozzle during the transfer of liquid steel from tundish to mould. They developed a Eulerian multiphase mathematical model using the finite difference program, CFX, and studied the three-dimensional (3D) turbulent flow of liquid steel and gas bubbles. The multifluid Eulerian multiphase model of CFX[6] was used to simulate the time-averaged KINNOR CHATTOPADHYAY, M. Engr. Candidate, MAINUL HASAN, Professor, MIHAIELA ISAC, Professor and Research Manager, and RODERICK I.L. GUTHRIE, Director and Professor, are with the McGill Metals Processing Centre, Department of Mining and Materials Engineering, McGill University, Montreal, Quebec, Canada H3A 2B2. Contact e-mail: [email protected]. Manuscript submitted February 22, 2009. Article published online September 11, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B
flow of argon bubbles within the liquid steel. In CFX modeling, each phase has its own set of continuity and momentum equations. Coupling is achieved through an empirical interphase drag between liquid steel and argon bubbles. The model predictions corresponded both quantitatively and qualitatively with measurements conducted using particle image velocimetry (PIV) on a 0.4-scale water model. G.M. Evans et al.[3] studied the flow characteristics of a down-flowing gas-liquid column that incorporated a submerged entry porous nozzle system. They developed the model based on the onedimensional drift flux analysis and critical Weber number for stable bubble size. The model was used to predict the bubble size and gas void fraction as a function of the gas and liquid flow velocities within the bubbly flow regime. It also could be used to predict the gas and liquid flow conditions at which the transition from bubbly to churn-turbulent flow occurs. Li Tao et al.[7] developed a mathematical model to s
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