Fluid flow and inclusion removal in continuous casting tundish
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I. INTRODUCTION
THE requirements regarding the improvement of quality of steel and performances achieved in ladle metallurgy lead us to consider the tundish not as a simple liquid steel container but as a real metallurgical reactor capable of appreciably diminishing the inclusion of the molten steel. Inclusions can greatly influence the properties of steel. The studies about improving the removal of inclusion from the molten steel in tundish are thoroughly carried out.[1–5] Kaufmann et al.[1] and Tacke and Ludwig[2] modeled fluid flow and inclusion removal based on the general viewpoint that inclusions tend to rise to the top surface slag with their Stokes velocities,[2] which come from the density difference between molten steel and inclusions, but the collision of inclusions and adhesion to the solid surface are ignored. Ilegbusi and Szekely[3] studied the turbulent collision and coalescence effect on inclusion removal in a tundish with electromagnetic force imposed on but only for inclusions with size of 20, 40, 60, 80, and 100 mm. Sinha and Sahai[4] took into account the buoyancy, turbulent collision, and adhesion to the solid surface, but not for every size. Sahai and Emi discussed the criteria for water modeling of the melt flow and inclusion removal in tundish, especially the criteria for collision and coalescence of inclusions. All the existing models had varying degrees of success in predicting the inclusion removal efficiency in tundish. However, none of the above investigations attempted to study the whole effect of inclusion size. Although the study of Sinha and Sahai[4] is for 12 sizes of inclusions, inclusions less than 25 mm in size were ignored. The following section of this article will verify that smaller inclusions have a much LIFENG ZHANG, Postdoctoral Fellow, Japan Society for the Promotion of Science, and SHOJI TANIGUCHI, Professor, are with the Department of Metallurgy, Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan. KAIKE CAI, Professor, is with the School of Metallurgy, University of Science and Technology Beijing, Beijing 100083, People’s Republic of China. Manuscript submitted February 22, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
larger collision removal rate and adhesion removal rate to the solid surfaces than bigger ones. On the other hand, other important collision modes, such as the Stokes collision, were not discussed. Also, all the studies on the inclusion removal in tundishes quoted the turbulent collision rate constant from Saffman and Turner[6] and took the coagulation coefficient as 1, in fact, because not all the inclusions colliding each other can coalesce for the reason of the force balance between the viscous force and van der Waals force; because some aggregates of inclusions will detach again, the coagulation coefficient must be less than 1. In this article, three-dimensional fluid flow velocity distributions of liquid steel in tundish with and without flow control devices are calculated. The results of the turbulent energy dissipation
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