Modeling study of the influence of turbulence inhibitors on the molten steel flow, tracer dispersion, and inclusion traj
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I. INTRODUCTION
THE new role of the tundish as a continuous metallurgical reactor is to provide steel to the continuous-casting mold at a desired flow rate, constant temperature, uniform chemistry, and low inclusion count. Fluid-flow-phenomena principles have been applied in the tundish to increase steel quality and productivity by improving molten steel cleanliness, decreasing refractory wear, increasing casting sequences, and controlling turbulence at the startup and grade-change operations. A general trend to attain those goals has been to increase the volume tundish size; this has been assumed to increase the flotation and removal of nonmetallic inclusions by increasing the overall residence-time distribution of liquid steel. However, the melt flow has to be optimized using flow-modifying devices in the interior of the tundish. Otherwise, the effects of the volume-capacity increase on the melt flow may have opposite results of those desired.[1] Small nonmetallic inclusions (less than 20 m in size) do not have enough buoyancy force to float and reach the slag layer. For this reason, the bulk flow should be redirected toward the top free surface in a controlled manner to maximize the contact time with the slag. For these purposes, different flow-modifying devices have been tried. Lately, turbulence-inhibiting designs have been used to reduce turbulence at the top free surface and to redirect the flow.[2,3,4] The turbulence inhibitor allows a reduction in the velocity gradients among the entry flow and the bulk flow inside the tundish, minimizing the disturbances on the slag layer and improving the cleanliness of the steel. In order to optimize steel flow and maximize the contact time of the inclusions with the slag layer inside the tundish, a study must be conducted to determine the optimum ´ PEZ-RAMIREZ and J. PALAFOX-RAMOS, Lecturers, and R.D. S. LO MORALES, Professor, are with the Department of Metallurgy and Materials Engineering, Instituto Polite´cnico Nacional-ESIQIE, Me´xico D.F., CP 07300. J. de J. BARRETO, Professor, is with the Materials Graduate Center, Instituto Tecnolo´gico de Morelia, Morelia Mich., Me´xico. D. ZACHARIAS, Research Engineer, is with FOSECO Inc., Cleveland, OH 44142. Manuscript submitted May 18, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS B
arrangement. This arrangement must be designed by considering the shape, the dimensions of the prototype, and the plant operating conditions of the tundish. Physical modeling and mathematical simulation are two complementary tools to simulate and evaluate the effects of the flow-control arrangements on the operating conditions of the tundish. A detailed knowledge of the molten steel flow is a prerequisite toward any effective flow-control optimization. In this study, these tools were used in a complementary fashion to simulate and evaluate the influence of a turbulence-inhibiting device on the velocity fields, tracer dispersion, small- and large-particle trajectories, flow-pattern characteristics, and grade changes in a large-volume tundish. F
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