Dynamics of two-phase downward flows in submerged entry nozzles and their influence on the two-phase flow in the mold

Gas-liquid flows inside the submerged entry nozzle (SEN) of a slab mold and their influence on the flow field in the mold were studied using video recording, mathematical simulations and Digital Particle Image Velocimetry (DPIV) approaches. Coalescence-breakup phenomena of bubbles in liquid steel flowing through a slab mold were studied using a water model. At low gas loads (ratio of mass flow rates of gas and liquid in the submerged entry nozzle) bubble dynamics consist of coalescence-breakup and dragged processes from the SEN until close to the narrow wall. At high gas loads, bubbles are accumulated close to the narrow wall where they coalesce, break and ascend toward the bath surface forming bubble swarms or descend along the narrow wall by dragging forces exerted by liquid phase on the surfaces of the bubbles. These swarms consist of coalescing bubbles and agglomerating groups of bubbles. The presence of bubbles in the flow decreases the magnitudes of vorticity values in the flow field of mono-phase flows. Thus, to increase the casting speed, the injection of argon should be adjusted to an appropriate level to avoid an excess of liquid entrainment to the flux phase. Bubbly and annular flows in the SEN yield structurally-uncoupled and structurally coupled flows in the mold, respectively. High gas loads at high casting rates lead to increases of bubble population and bubbles sizes due to coalescence processes whose rate exceeds that of their breakup. The presence of gas bubbles or gas layers inside the SEN lead to periodical twisting of the liquid flow that induces biased flows through both ports yielding uneven flows in the mold. A multiphase mathematical model predicts acceptably well the flow dynamics of two-phase flows inside the SEN.