Optimized Fluid Flow Control System for a Tundish Used in Frequent Steel Grade Change Operations

A slab caster with a wide casting mix carries high-frequency steel grade changes using a small, 14 ton capacity tundish and needs to decrease the intermixed steel tonnage. Testing different tundish arrangements, through a water one-third scale model, permits a flow control design to decrease the amount of mixed steel. A computer fluid dynamics approach, based on the Realizable k-epsilon model, replicates the experimental results. It helps to elucidate the role of the tundish filling rate, finding that increasing it increases the dissipation rate of kinetic energy coming out from the turbulence inhibitor. At high filling rates, the degraded kinetic energy of the downstream flow drives the residues of the "old" steel, prolonging the intermixing phenomena. In its later stages, the intermixing phenomena imply diffusion and transport on small scales, and both are governed by the Schmidt number given by the ratio of the Batchelor and Kolmogorov length scales, according to lB eta=Sc-1/2. The Schmidt, Sc, numbers in steel are in the range of 28-440. These large Sc numbers mean that the diffusion process must reach the dissipative scales of turbulence, that is, beyond Kolmogorov ' s scale, to achieve a complete mixing at microscale levels.