A Study of Bubble and Inclusion Behaviors in a Liquid Steel Bath

The bubble formation processes in a water model experiment were measured by a high-speed camera. Nozzle diameters of 0.5 mm, 1 mm and 2 mm were investigated under both wetting and non-wetting conditions. The bubble sizes and formation frequencies as well as the bubbling regimes were identified for each nozzle size and for different wettabilities. The results show that the upper limits of the bubbling regime were 7.35 L/h, 12.05 L/h and 15.22 L/h under wetting conditions for the 0.5 mm, 1 mm and 2 mm nozzle diameters, respectively. Meanwhile, the limits were 12.66 L/h, 13.64 L/h and 15.33 L/h for the non-wetting conditions. In addition to experiments, numerical modeling was performed. The Volume-of-Fluid (VOF) method was used to track the interface between the gas and liquid. The simulation results were compared to experimental observations from an air-water system. The comparisons show a satisfactory good agreement between the two methods (maximum difference is 0.029 s during a bubble formation period). Simulations from the argon-steel system show that the effect of the nozzle size on the bubble formation is insignificant for the current studied metallurgical conditions. The upper limits of the bubbling regime were approximate 60 L/h and 80 L/h for a 2 mm nozzle for wetting and non-wetting conditions, respectively. In addition, a poor wettability leads to a bigger bubble size and a lower frequency compared to a good wettability, for the same gas flow rate. The fundamental aspects of rising argon bubbles in molten metal flow were investigated by numerical simulations. The results show that 3~10 mm bubbles rise in a spiral way with strong instabilities which cause them to change their instantaneous shapes. In addition, 10~20 mm bubbles rise rectilinearly and their shapes are kept almost steady. All these bubbles’ terminal velocities are around 0.3 m/s, which are in accordance with literature data. The simulation results of bubble bursting at the liquid surface show that when the surface tension is 1.4 N/m, the critical bubble size is 9.3 mm. Also, the ejection is found to increase with an increased surface tension value, unless a critical bubble size is reached. The single bubble passage through the liquid-liquid interface was numerically simulated. The calculation results show that the passing patterns at the steel-slag interface are oscillation-pass, oscillation-breakup, oscillations-pass, pass and pass-breakup for the 3, 5, 7, 10 and 15 (20) mm bu