Avoiding particle entrapment into the solidifying shell of a steel continuous caster is important to improve the quality of the continuous cast product. Therefore, the fluid flow dynamics in the steel melt and mushy zone, heat transfer and solidification of the steel shell, as well as the motion and entrapment of inclusion particles during the casting process were investigated using computational models. Solidification of the strand shell is modelled with an enthalpy‐formulation by assuming a columnar morphology in the mushy zone. The motion of particles is tracked with a Lagrangian approach. When the particles reach the solidification front, they can be entrapped/engulfed into the solid shell or pushed away from the solidification front, depending on the mushy zone morphology and the forces acting on them. The current paper focuses on the mould region at a steel continuous caster, including the submerged entry nozzle (SEN) and 1.2 m length of the strand. The results are validated with plant measurements and demonstrate the potential of the model to predict fluid flow, shell growth and the positions and the amount of entrapped/engulfed particles in the solidifying strand.
In addition to corrosion resistance and processing properties, high coating uniformity is a key quality criterion for galvanized steel sheets. Hydrodynamic gas jet wiping has proved to be an efficient method to control the coating thickness. However, the occurrence of nonuniformities is attributed to the unsteadiness of the impinging jet. For the first time, vertical surface non-uniformities resulting from the interaction of the impinging jet with the liquid coating are numerically predicted under industrial boundary conditions using the ANSYS Fluent 1 . The turbulent flow field of the compressible wiping gas is accomplished by the LES (Large-Eddy-Simulation) turbulence model, whereas the interphase between the wiping gas and the liquid coating is modeled by the VOF (Volume-of-Fluid) method. It is found that the liquid coating reacts relatively slowly to the high frequent flapping gas jet. Only, when the jet is deflected for a comparatively long period, significant waves are able to develop. The waviness predicted by the simulation model is in good agreement with experimental results. Thus, the model enables a careful study of process settings on the vertical coating uniformity characteristics. For the studied case, an increase of nozzle inclination is found to enhance the performance in terms of coating uniformity significantly.
A mixture solidification model is employed to study the interaction between the melt flow and the growing mushy zone. The goal is to address the importance of considering the melt flow and flow pattern (laminar or turbulent) in the growing mushy zone. A simple 2D benchmark with parallel flow passing by/through a vertically growing mushy zone is considered. Parameter studies with different velocities and flow patterns are performed. It is found that the flow velocity and flow pattern in and near the mushy zone plays an extremely important role in the formation of the mushy zone. The mushy zone thickness is dramatically reduced with the increasing melt velocity. Simulations with/without considering turbulence show significantly different results. The turbulence in the mushy zone is currently modeled with a simple assumption that the turbulence kinetic energy is linearly reduced with the mush permeability.
Gas-Jet wiping is a widely applied technology in continuous galvanizing mills, which enables the adjustment of the specific coating mass by an impinging turbulent gas-jet. The unsteady impingement conditions, however, are reported to cause surface non-uniformities such as waves. In this study, proper orthogonal decomposition (POD) is used to analyze an industrial gasjet wiping process. POD allows to objectively extract the most dominant flow structures (modes) and their dynamics from the impinging jet. The acquisition of the necessary temporally and spatially highly resolved flow data is done by a LES-VOF simulation model. The POD analysis shows that jet flapping and axial fluctuations of the jet core are the most dominant spatial modes in the studied case. The frequency range of the modes as well as the frequency range of the height fluctuations of the impinged film are compared in a spectral analysis. Additionally, it is shown that slight changes, for example, the absence of the thin liquid film on the impinged surface, alters the frequency range of the dominant POD modes, whereas the modes themselves remain mostly unchanged.
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