Flow patterns of liquid steel in a thick slab mold, fed by bifurcated nozzles, are modeled through water modeling using characterization techniques such as particle image velocimetry (PIV), ultrasound velocimetry probe (UPV), and mathematical simulations using the large eddy simulation (LES) model. Geometries of nozzle ports include circular and square shapes with similar cross‐section area. Square ports deliver wandering jets that occupy about 66% of the port area, and are raveled during their pass through the mold impacting the narrow face. Circular ports deliver compact jets mainly through the lower edge occupying only about 45% of the port area. The analysis of the flow structures indicates that the circular ports form more turbulent jets than square ones for the same flow rate of liquid. Mathematical simulations, using the LES model, predict acceptably well measured velocity fields. Slag entrainment through mechanisms of shear‐drag forces at the metal–slag interface is estimated through a critical capillary number which involves slag viscosity, interfacial tension, and fluid velocity. At deep nozzle immersions, this capillary model predicts more slag entrainment using the bifurcated nozzle with circular ports.

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Turbulent flow when steel is delivered through a nozzle in a slab mold induces dragging forces at the metal-slag interface that entrain slag droplets into the metal bulk. These dragging effects are discontinuous and correspond to the velocity fluctuations of turbulence at that interface which themselves, are dependent on nozzle immersion, nozzle design, mold width and casting speed. Slag viscosity and density, metal viscosity and slag layer thickness are employed to estimate that critical velocity which is embodied in a critical capillary number for some established mold operating conditions. This approach permits the link between all operating variables including flux chemistry and nozzle design with the interface instability. A relationship between the capillary number and the magnetic field strength used to brake the liquid steel is established which is used to assure the interface stability for any operating condition and flux chemistry.

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