Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

Abstract

A numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM®. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a “multiroll” flow pattern in the mold. This phenomenon can be explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple damping effect; depending on the field strength, its action is found to be topologically complex.

Analysis of a New SEN Design with an Inner Flow Divider

“…These differences, in turn, generate an asymmetric hydrodynamic behavior inside the mold. Recently, Vakhrushev [5] reported that growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related to the formation of a "multi-roll" flow pattern in the mold. On the other hand, several works have reported that the sustained switching of the fluid flow pattern inside the SEN bottom zone can also produce considerable differences between the jets emerging from the nozzle [6,7].…”

Effect of Electromagnetic Brake on Transient Asymmetric Flow, Solidification, and Inclusion Transport in a Slab Continuous Casting

“…When EMBr is applied, with a B U of 0 T, the braking effect is not achieved, and the surface velocity increases to some extent; one possible explanation for this phenomenon is that the jet flows are uplifted under current location of lower coil, resulting in the excessive surface velocity. [ 37 ] When the magnitude of B U increases, the surface velocity decreases significantly, as does the velocity gap between the two halves of the mold, implying that the asymmetry of the flow field has improved under the influence of EMBr.…”

Modeling Asymmetric Flow in the Thin‐Slab Casting Mold Under Electromagnetic Brake

“…[22] A recent study of the EMBr effect on the nonmetallic inclusions removal was done by Yin et al [23] An advance technique, combining a mold EMBr and a strand electromagnetic stirring (SEMS) to enhance uniformity of the solidification, was presented by Wang et al [24] Another new approach, introducing two vertical magnetic poles (VMPs) in a freestanding and adjustable EMBr (FAC-EMBr) to weaken the jets interference with the shell and meniscus region, was proposed by Li et al [25] Nowadays, the advance numerical modeling technique resulted in the numerous studies on this topic. [24,[26][27][28][29] In the presented study, the coupled solidification and magnetohydrodynamics (MHD) models, previously developed and verified by the current authors, [30][31][32][33] implemented in the open-source computational fluid dynamics (CFD) package OpenFOAM, [34] are applied to simulate the effects of the electromagnetic braking on the asymmetric melt flow caused by the partial SEN clogging.…”

“…Nowadays, the advance numerical modeling technique resulted in the numerous studies on this topic. [ 24,26–29 ] In the presented study, the coupled solidification and magnetohydrodynamics (MHD) models, previously developed and verified by the current authors, [ 30–33 ] implemented in the open‐source computational fluid dynamics (CFD) package OpenFOAM, [ 34 ] are applied to simulate the effects of the electromagnetic braking on the asymmetric melt flow caused by the partial SEN clogging.…”