Modeling of biased flow phenomena associated with the effects of static magnetic-field application and argon gas injecti
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I. INTRODUCTION
THE trend toward increased production with higher casting speeds from a conventional continuous caster has emphasized the importance of maintaining a stable and relatively quiescent meniscus in the slab continuous-casting mold. However, the molten steel flow in a mold is unstable, and different types of biased flow exist, specifically for high casting speeds. These include off-center placement of a submerged entry nozzle (SEN), periodic oscillations and random fluctuations due to argon gas injection and turbulence, etc. Vortexing is generally associated with draining of a metallurgical vessel.[1] As the vessel is drained, a slag-entraining vortex appears as the bath reaches a critical depth. This vortex is composed of a downward flow toward the outlet and a planar vortex (two-dimensional rotation of fluid). It is believed to be a significant contribution to mold powder entrapment; the entrapped flux may be carried deeply down into the mold by downward flows and results in the uncleanness of the steel. Water modeling studies have revealed the existence of the vortex in the slab mold adjacent to the SEN.[1,2,3] Wang[1] reported the appearance of a vortex adjacent to the SEN. The results from surface-quality and sliver-defect analysis revealed that most defects occurred at the middle of the slab width, which suggested that the vortex may be a source of slag entrapment and sliver defects. He[2] concluded that the existence of a vortex in the mold was the result of biased BAOKUAN LI, Professor, is with the Department of Thermal Engineering, The School of Materials and Metallurgy, Northeastern University, Shenyang, 110006, P.R. China. TOSHIMITSU OKANE, Research Associate, and TAKATERU UMEDA, Professor, are with the Department of Metallurgy, Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan. Manuscript submitted April 19, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
flow between the SEN ports, generated by the effects of the slide gate, nozzle clogging, turbulent flow, etc. Using a series of flow visualization experiments, Gebhard et al.[3] found that this vortexing had the same mechanism as what is commonly termed a “bathtub vortex,” and the surface velocity affected the depth and stability of the vortex. The study of Honeyands and Herbertson[4] shows the biased flow at high casting speeds to be caused by transients. Gupta and Lahri[5] illustrate the biased flow caused by geometrical conditions of the mold. Huang and Thomas[6] studied the transition from biased flow to symmetrical steady flow by changing the nozzle inlet conditions, but they did not mention a vortexing phenomenon. Argon gas is added to the SEN during continuous casting to deter clogging by solid inclusions. It also affects the flow pattern in the mold. Some research efforts have been dedicated to elucidating gas-liquid flow dynamics, both experimentally with physical water models and numerically with mathematical models.[7,8] Application of a static magnetic field, which is known as the electromagnetic b
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