Gas-Liquid Reaction Model in Gas-Stirred Systems: Part 1. Numerical Model
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injection of inert gas (argon or nitrogen) is used in many steelmaking processes to promote stirring of liquid steel and chemical reactions, to remove particulates, to achieve chemical and thermal homogenization and to eliminate the possibility of steel solidification close to the ladle walls. The stirring gas introduced into the melt through the ladle bottom produces a circulatory flow pattern inside the liquid steel (Figure 1), which is significant for the distribution and residence time of the alloys injected into the ladle, for the separation of nonmetallic inclusions, for the emulsification of the slag phase and for the kinetics of different reactions among the phases: gas, molten steel, and slag.[1] The discharge of gas into a liquid produces the ‘‘suction’’ of liquid in the lowest part of the system and its drive in a vertical direction. This phenomenon, in addition to the radial turbulent diffusion exerted on the dispersed phase during its vertical rising, enlarges the two-phase zone diameter, which consequently acquires a characteristic conical shape (Figure 1). The ascending gas is completely discharged once the steel reaches the surface and the remaining liquid completes the circulation flow along the ladle walls.[1] Immediately above the injector, the disintegration of the gas stream into bubbles takes place. In this regime, called the momentum region, the gas transfers its initial momentum to the liquid. At some distance upward, the disinteGABRIELA VENTURINI, formerly Research Assistant, Center for Industrial Research, Tenaris B2804MHA, Campana, Argentina, is Graduate Student, California Institute of Technology, Pasadena. MARCELA B. GOLDSCHMIT, Head, Computational Mechanics Department, is with the Center for Industrial Research, Tenaris B2804MHA, Campana, Argentina. Contact e-mail: mgoldschmit@ tenaris.com Manuscript submitted February 6, 2006. Article published online May 30, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
gration of the gas stream is completed and the bubble zone, or buoyancy region, becomes fully developed. This regime is similar to a one-phase plume driven by density differences and is usually called two-phase plume. Consequently, liquid motion is caused by momentum transfer from the gas jet in the zone close to the injector and by the buoyancy force of the bubbles in the preceding region. The transition between those two regions may be taken as the development height, z0, that is, the distance from which the bubble/liquid mixture is fully developed.[2] Mazumdar et al.[3] reported that, under typical ladle operation, hydrodynamic conditions at the injector only marginally influence the physical characteristics of the two-phase plume (except in the surroundings of the nozzle/orifice). Unlike most refining reactions in steelmaking, such as the refining reaction for silicon, manganese, sulfur, or phosphorus, dissolved nitrogen is not removed by slagmetal reactions but by special treatments such as vacuum degassing, in which a carrier gas (argon) is injected into a liquid steel vessel whose atmosp
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