Numerical simulation on gas–liquid multiphase flow behavior under coupling effects of annular gas curtain and swirling flow at tundish upper nozzle

A three-dimensional mathematical model has been established for a novel metallurgy process coupling an annular gas curtain with swirling flow at tundish upper nozzle. The discrete phase model and volume of fluid model were applied to simulate the gas–liquid multiphase flow behavior in tundish and nozzle. The effect of argon flow rate on the migration behavior of bubbles and interface behavior between steel and slag was also investigated. The presented results indicate that the novel coupling process can significantly change the flow pattern in the stream zone of a tundish, prolong the average residence time of liquid steel, and reduce the dead fraction. A complete annular gas curtain is formed around the stopper rod of tundish. Under the action of drag force of liquid steel, a part of small bubbles enter the nozzle through the swirling grooves and gather toward the center of the nozzle by centripetal force. As the argon flow rate increases, the volume fraction of argon gas entering the nozzle increases, which enhances the swirl intensity and increases the concentration of bubbles in the nozzle. To avoid the formation of slag open eye in tundish, the argon flow rate should not exceed 8 L min−1.

Flow and heat transfer of liquid slag in a continuous casting mold

A three-dimensional mathematical model for coupled liquid steel and liquid slag was established to study the flow and heat transfer behavior of liquid slag. Based on the volume of fluid method and the heat transfer model, the effect of different casting parameters on the flow and heat transfer of the liquid slag was investigated. The results show that there are two different size recirculation zones of the liquid slag layer on the liquid steel in the mold center plane, extending from the submerged entry nozzle to the mold narrow face. With the increase in the casting speed and the decrease in the viscosity of the mold flux, the overall velocity and the temperature of the liquid slag increase. With the increase in the inclination angle and the submergence depth of the submerged entry nozzle, the temperature of the liquid slag decreases, and the velocity decreases near the mold narrow face and increases in the vicinity of the submerged entry nozzle. The inactive flow field and the low temperature of liquid slag within 100 mm of the submerged entry nozzle may intensify the surface longitudinal cracking sensitivity of the slab. When the lubrication and heat transfer are well regulated between the surface of mold and the mold flux film, low casting speed, large inclination angle and submergence depth of the submerged entry nozzle are beneficial for reducing the possibility of a slab surface longitudinal crack.

Effects of argon blowing at tundish upper nozzle on multiphase flow behavior in nozzle

In continuous casting,the argon blowing at the tundish upper nozzle is usually used to prevent nozzle clogging,whose effect is closely related to the migration of argon bubbles and the flow behavior of the liquid steel in the nozzle.Here,to investigate the effects of argon blowing at the tundish upper nozzle on multiphase flow behavior in nozzle,a threedimensional model of the tundish–nozzle–mold was established for numerical simulation.The results indicate that the argon bubbles injected from the inner wall of the tundish upper nozzle first move downward along the nozzle wall under the action of the liquid steel.As the distance from the tundish upper nozzle increases,the argon bubbles gradually diffuse to the center of the nozzle.Compared with no argon blowing,the liquid steel velocity increases in the center of the nozzle and decreases near the wall with argon blowing.With increasing the argon flow rate,the concentration of bubbles in the nozzle increases,and the process of bubble group diffusion to the center region of the nozzle speeds up.This in turn increases the liquid steel velocity at the center of the nozzle but reduces near the wall.With increasing the casting speed,the concentration of bubbles in the nozzle decreases,the length of the bubble group near the nozzle wall is extended,and the liquid steel velocity at the center region and near-wall region of the nozzle increases.The mechanism of argon blowing at the tundish upper nozzle to prevent nozzle clogging is mainly realized by the isolation effect of the argon bubble group on the inner wall of the nozzle.