Browsing by Author "Mabentsela, Arthur"
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- ItemNumerical and physical modelling of tundish slag entrainment in the steelmaking process(Stellenbosch : Stellenbosch University, 2015-12) Mabentsela, Arthur; Akdogan, G.; Bradshaw, S. M.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Extensive work has been published in the open literature concerning the flow patterns in bare tundishes and tundishes furnished with flow control devices. However, very little work has been published on the entrainment of tundish slag. The aim of this research was to study (physically and numerically) tundish slag behaviour in a bare tundish and a tundish furnished with a flow control device (FCD). Furthermore, to identify, if any, the mechanisms for tundish slag entrainment in a bare tundish and a tundish fitted with a flow control device and to make recommendations based on the findings of this study. The physical modelling was done in a 1:2 reduced scale model of an industrial tundish such as was studied by Kumar et al. (2008). In the physical model, water was used to model the steel phase while paraffin was used to model tundish slag. The numerical modelling was done in ANSYS Fluent 14.5. The Volume of Fluid (VOF) model was used to model the interface between the two phases (paraffin and water). Turbulence was modelling by making use of the Realizable k- ɛ model. Observations made whilst the model was running showed that the steel-slag interface remains immobile even in the FCD case. Furthermore entrained paraffin formed small droplets, approximately 1 mm in diameter. These droplets could be seen in small numbers throughout the tundish. Results from the physical model showed that in both the bare tundish and tundish with a FCD, areas of high concentrations of entrained slag exist near the inlet region. The entrained slag concentration decreases towards the tundish end walls. A numerical model that can be used to model tundish slag behaviour was developed using the VOF model with a mesh size of 1.4 mm at a time step of 0.125 s for the bare tundish and a tundish fitted with a FCD. The model predicted similar entrained slag patterns as those of the physical model. Analysis of flow patterns and velocity magnitudes tangential to the steel-slag interface showed that slag entrainment in both the bare tundish and tundish with a flow control device possibly takes place via two mechanisms. First the slag moves across the steel-slag interface via mass transfer, secondly small velocities tangential to the interface, 3 x 10-³ m/s for the bare tundish and 1.5 x 10-² m/s for the FCD case, at depth of greater than 10 mm below the interface carry the already “entrained” slag into the bulk steel phase. These tangential flow patterns are dominant in the inlet shroud and are to be found in both the bare tundish and in the tundish with a FCD, hence the high concentration of entrained slag in this region.