X-RAY FLUOROSCOPIC OBSERVATION OF BUBBLE CHARACTERISTICS IN A MOLTEN IRON BATH

The formation of bubbles at a nozzle and subsequent rising behavior of them in a molten iron bath at 1 250 degrees C were observed using a h igh-voltage X-ray fluoroscope and a high-speed video camera. The frequ ency of bubble formation at the nozzle exit, the mean bubble diameter and the mean bubble rising velocity were obtained for a wide range of injected argon gas flow rate. Empirical correlations of these quantiti es were proposed and compared with previously published experimental d ata and empirical correlations. It has been commonly believed that the frequency of bubble formation at a nozzle placed in a molten metal ba th depends solely on the gas flow rate and the outer diameter of the n ozzle when the gas flow rate is relatively high and the wettability be tween the nozzle material and the molten metal is bad. The present exp erimental results, however, revealed that the frequency of bubble form ation has a close relationship not with the outer diameter but with th e 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 co ming from the nozzle exit was approximately 50 cm(3)/s under the prese nt experimental conditions. The bubble behavior near the bath surface also was made clear.