The formation of bubbles at a nozzle and subsequent rising behavior of them in a molten iron bath at 1250°C were observed using a high-voltage X-ray fluoroscope and a high-speed video camera. The frequency of bubble formation at the nozzle exit, the mean bubble diameter and the mean bubble rising velocity were obtained for a side range of injected argon gas flow rate. Empirical correlations of these quantities were proposed and compared with previously published experimental data and empirical correlations.
It has been commonly believed that the frequency of bubble formation at a nozzle placed in a molten metal bath depends solely on the gas flow rate and the outer diameter of the nozzle when the gas flow rate is relatively high and the wettability between the nozzle material and the molten metal is bad. The present experimental results, however, revealed that the frequency of bubble formation has a close relationship not with the outer diameter but with the inner diameter of the nozzle for a higher gas flow rate. Furthermore, the bubble frequency depended on the gas flow rate and the physical properties of gas and molten metal. The critical gas flow rate for the initiation of small bubbles due to disintegration of large bubbles coming from the nozzle exit was approximately 60 cm³/s under the present experimental conditions. The bubble behavior near the bath surface also was made clear.