Effect of an Electromagnetic Brake on the Turbulent Melt Flow in a Continuous-Casting Mold
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ve relationship between the quality of the solidified steel products and the properties of the melt flow during the continuous-casting process has been demonstrated in many studies (for instance, see Reference 1 and the references therein). The application of various magnetic fields provides an innovative and efficient tool for an effective and contactless flow control (FC) in the mold, which facilitates substantial capabilities to improve the quality of the steel and to enhance the productivity of the process. The principle of an electromagnetic brake (EMBR) employs a static magnetic field aligned perpendicular to the main flow direction. It relies on the interaction between the electrically conducting melt and the applied magnetic field resulting in a retarding force to slow down the mold flow and to damp strong velocity fluctuations. A uniform reduction of the melt flow especially in the neighborhood of the jet emerging from the submerged entry nozzle (SEN) is the main goal of the FC because violent flows at high velocities are supposed to cause
XINCHENG MIAO and KLAUS TIMMEL, Ph.D. Students, SVEN ECKERT, Department Head, and GUNTER GERBETH, Director, are with the MHD Department, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), 01314 Dresden, Germany. Contact e-mail: [email protected] DIRK LUCAS, Department Head, is with the CFD Department, Helmholtz-Zentrum Dresden-Rossendorf (HZDR). ZHONGMIN REN, Professor, is with the Key Laboratory of Metallurgy & Materials Processing, Department of Materials Science and Engineering, Shanghai University, Shanghai 200072, P.R. China. Manuscript submitted February 2, 2012. Article published online May 8, 2012. 954—VOLUME 43B, AUGUST 2012
an entrapment of bubbles or nonmetallic inclusions impairing, therefore, the steel cleanliness significantly. Although various EMBR designs have already been adopted for industrial use for more than 20 years,[2,3] the impact of a direct current (DC) magnetic field on such highly turbulent and complex flows is a complicated phenomenon and has not been fully understood until now. Contrary to the usual expectations, static magnetic fields may even destabilize liquid metal flows. Respective indications have been found in convection experiments in liquid metals, where it could be demonstrated that a weak DC magnetic field can enhance the convective heat transfer.[4–6] First, direct observations of the destabilizing effect on the velocity field by an applied DC magnetic field were reported by Zhang et al.,[7,8] who considered the imposition of a horizontal magnetic field on a bubble-driven flow inside a cylindrical liquid metal column. For a certain parameter range, the DC magnetic field gives rise to the development of distinctive transient flow pattern with increased turbulent perturbations. A similar effect has been shown recently by Timmel et al.[9] for the mold flow within a small-scale mockup of the continuous-casting process. Furthermore, it is worth noting that the phenomenon of magnetorotational instability exists, where a laminar flow is made turbulent by the influence of a
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