Dynamics of coupled and uncoupled two-phase flows in a slab mold
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Dynamics of Coupled and Uncoupled Two-Phase Flows in a Slab Mold R. SÁNCHEZ-PÉREZ, R.D. MORALES, L. GARCÍA-DEMEDICES, J. PALAFOX RAMOS, and M. DÍAZ-CRUZ Two-phase flows in a mold of a slab caster are studied using water modeling, particle-image velocimetry (PIV), and computational fluid-dynamics techniques. Two-way coupled flows are observed in liquidgas systems, because both phases influence each other’s momentum transfer. In addition to this concept, PIV measurements indicate the existence of structurally coupled flows, where the velocity vectors of both phases observe similar orientations. When the drag forces of the liquid, exerted on the bubbles, exceed a certain value of the inertial forces of the liquid phase, at high mass loads of gas (ratio of mass flow rates of the gas phase and the liquid phase), the flow becomes structurally coupled. These types of flows promote large oscillations of the meniscus level. Two jets, liquid and bubble, were identified; the latter always reported larger angles than the first, independent of the gas load. Thus, a gas-rich jet is located closer to the lower edge of the submerged entry nozzle (SEN) port, and the liquid-rich jet is found above this position. The liquid-jet angle approaches that of the SEN port when the flow becomes structurally coupled. Structurally uncoupled flows report gas jets that follow torrenttype patterns which are well explained using a multiphase fluid-dynamics model. Structurally coupled flows yield gas jets with a continuous pattern.
I. INTRODUCTION
TURBULENT flow in the continuous casting process involves multiphase flow and transport phenomena and plays the most important role in the quality of steel. As shown in Figure 1, the molten steel entering the mold may carry inclusion particles (alumina, silicates, etc.) and drags argon bubbles. Liquid flux can also be entrained from the shear of the liquid flow across the top surface, forming harmful inclusions. These inclusions and bubbles will either be safely transported to the top surface and removed by the slag layer, or become entrapped in the shell, at the solid/liquid interface of the solidifying metal. The turbulent flows are essentially of unsteady and fluctuating natures, producing an uneven and asymmetrical distribution of defects in slab products. Since bubbles influence radically the fluid-flow patterns in a mold, a first step in the study of transport phenomena in molds is the analysis of twophase flows. Steel motion in the mold interacts with argon bubbles injected through the submerged entry nozzle (SEN), and both phases observe two-way coupled momentum-transport phenomena. Argon bubbling is also responsible for the amount of liquid carried out to the metal/flux interface, and, when gas flow is in excess, entrainment of flux into the metal bulk has been reported as an important source of inclusions.[1,2] Other effects of gas bubbling include heat transfer and temperature profile R. SÁNCHEZ-PÉREZ and L. GARCÍA-DEMEDICES, Graduate Students, J. PALAFOX RAMOS, Sen
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