Prediction of mass transfer between liquid steel and slag at continuous casting mold

Abstract

For the prediction of steel desulphurization and dephosphorization or the evolution of slag composition at continuous casting mould, mass transfer between two immiscible fluids in a turbulent situation should be calculated. For this purpose, two possibilities are offered for the simulation. The first one consists in the calculation of the local chemical equilibrium with the simultaneous prediction of the species transport, but the cost is that very fine mesh should be used. The second is based on the assessment of the mass transfer coefficient from hydrodynamic calculations and further use of thermodynamic code fed with interface area and transfer coefficients. On a computing time point of view, this second method is more affordable for 3D configurations than the first one, but it is less accurate. Literature survey indicates that it is possible to obtain a realistic evaluation of the mass transfer coefficient from hydrodynamic calculations, under the condition of very precise description of the flow near the interface. The paper explains the reasons for the different simplifications which were made to predict the mass transfer between liquid steel and slag, gives indication on interest and limitation of the coupling between fluid dynamics and thermodynamics to get the local and time dependent evolution of chemical composition in the two phases. The modelling to predict the mass transfer coefficient is also described and compared to correlation proposed in the literature. Finally, a correlation is proposed to get mass transfer coefficient up to Schmidt number = 1000.