2017 Volume 57 Issue 9 Pages 1553-1562
Vortexing in continuous slab casting mould is a complex inter-related phenomenon of multiphase fluid flow which can entrain mould powder and deteriorate the end product quality. In this contribution, a 0.4-scale water model has been employed to investigate the interactive effects of the operational parameters including, partial clogging of SEN ports, water flow rates, submerged entry nozzle (SEN) immersion depth and air flow rates. Operating conditions like higher values of air flow rates and deeper submergence depth of the SEN are found to reduce vortex frequencies. At higher air flow rates, bubbles emerging from the SEN port would have higher diameter and hence higher terminal velocity. Also, at higher air flow rates, volume fraction in the vicinity of the SEN is high. Raising larger bubbles with high volume fraction and high terminal velocities, during their interaction with the liquid flow streams approaching the meniscus, would reduce the horizontal velocity components to very low values. As a consequence, the shearing effect between the liquid streams fast approaching the SEN would be decreased, leading to reduction in vortex frequencies. The bubble rising pattern along with the upper circulation loop is found to vary with the SEN submergence depth. At deeper submergence depth, larger fraction of gas bubbles traversing along the upper recirculation loop would reach to a point which is very close to the SEN and escape into atmosphere from there. On contrary, this point of contact between gas bubbles and the meniscus is comparatively away from the SEN at shallow submergence depths. As known, vortices are formed in the vicinity of the SEN where the shearing effect is the maximum. In case of deeper submergence depth, the ascending gas bubbles interact with the swirling and reduce the shearing effect and hence the vortex formation. These findings of the current study are important in controlling the mould powder entrainment through vortexing.