WATER MODEL EXPERIMENT ON THE BUBBLE BEHAVIOR IN A CYLINDRICAL VESSEL UNDER REDUCED PRESSURES

As a fundamental study on the RH and DH degassing processes, air was injected into a cylindrical water bath under a reduced surface pressure through a centered single-hole bottom nozzle. The shape of bubbles during expansion near the nozzle and the subsequent dispersion of the bubbles in the course of rising in the bath were observed using a high -speed video camera. The bubble characteristics such as gas holdup, bubble frequency, mean bubble rising velocity, mean bubble diameter were measured with a two-needle electro-resistivity probe. The frequency of bubbles generated at the nozzle exit under reduced pressure agree with that formed under the atmospheric pressure and the same mass flow rate. Accordingly the effect of reduced pressure on the frequency of bubble formation is negligible. Bubbles generated under reduced pressures expanded near the nozzle up to the volume associated with the hydrostatic pressure. The bubble characteristics in the region away from the nozzle were satisfactorily approximated by those observed for gas injection under the atmospheric surface pressure and the same volumetric gas flow rate. The total interfacial area between bubbles and liquid under reduced pressures was also determined as one of influential parameters for the metallurgical reactions occurring in a bath with gas injection. It was dependent on the square root of the gas flow rate after expansion, and an empirical equation of it was proposed.