Visualization of Liquid Metal Two-phase Flows in a Physical Model of the Continuous Casting Process of Steel
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ZLE clogging has to be considered as a serious adverse event with respect to a failure-free operation of the tundish-mold system in continuous casting machines. The regulation of the steel flow from the tundish into the nozzle by a stopper rod or sliding gate causes a constriction of the flow path, which leads to a pressure drop in the SEN. If the pressure inside the nozzle falls below the atmospheric pressure air aspiration through the porous refractory could occur. Oxides are formed, which may stick at the inner nozzle wall. The consequential gradual reduction of the effective nozzle cross section may change the flow pattern in the mold. Such a process involves a significant risk for worsening of the quality of steel products. Argon gas is added to the flow in many cases to avoid clogging inside the casting nozzle. Moreover, the argon bubbles are supposed to drag alumina particles into the mold and transport them toward the slag layer at the free surface. On the other hand, the gas injection leads to highly turbulent and KLAUS TIMMEL, Ph.D. Student, NATALIA SHEVCHENKO, Research Assistant, MICHAEL RO¨DER, Assistant, SVEN ECKERT, Head of Department of Magnetohydrodynamics, and GUNTER GERBETH, Director of Institute of Fluid Dynamics, are with the Department of Magnetohydrodynamics, Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Bautzner Landstr. 400, 01328 Dresden, Germany. Contact e-mail: [email protected] MARC ANDERHUBER, Senior Research Engineer, and PASCAL GARDIN, Fluid Dynamics Expert, are with the Industrial Operations Center, ArcelorMittal, Maizie`res Research S.A., 57283 Maizie`res-lesMetz, France. Manuscript submitted September 17, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
complex two-phase flows, which are difficult to predict by numerical simulations. The injected gas bubbles have a distinct influence on the flow pattern and may trigger instabilities in the mold, for instance, observations made on real casters showed correlations between argon gas pressure variations in the submerged entry nozzle (SEN) and mold meniscus perturbations.[1] Gas–liquid flows within the SEN and the mold have been addressed by many studies, whereas previous contributions to a better understanding of complex two-phase flows in metallurgical processes have been obtained by a combination of numerical modeling and up to 1:1-scale water models[2– 15] and experimental trials at real casting machines.[1,16] Bai and Thomas[4] used 3-D numerical simulations and a water model to investigate the effect of argon bubbles on the turbulent steel flow in a sliding gate configuration. They found that the discharging jet from one port may split into two separate jets in the mold. The upwards jet carriers a high percentage of gas, while only a few gas bubbles are observed in the downward liquid jet. The jet splitting occurs somewhat arbitrary and depends on nozzle geometry, argon injection, or a swirling behavior of the jet. An increasing gas flow rate bends the upper jet upwards and enhances turbulence. The splitting phenomenon of
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