Experimental study of bubbling regimes on submerged micro-orifices

The dynamic bubble behaviors on submerged micro-orifices are investigated experimentally. The orifice diameters are within the range of 0.11–0.24 mm, and the range of gas flow rate is between 0.167 and 25 ml/min. The experimental data were recorded using a high-speed camera, and images were analyzed with the help of MATLAB. The bubble formation processes on the submerged micro-orifices show some new and different dynamic behaviors, such as multi-bubble coalescence, and the alternate appearance of paring and single bubbles. At low Bond numbers (variation in the orifice radii), with an increase in Weber number (variation in the gas flow rate), a bubble first emerges during a single period stage followed by a multi-bubble coalescence stage. The bubble coalescence processes can be divided into five cases according to the number of coalescing bubbles. With an increase in the gas flow rate, it was found that the complete bubble detachment time and the detachment volume increase. Meanwhile, based on an analysis of the bubble aspect ratio and rising velocity, departing bubbles were shown to suffer stronger oscillations. At a higher Bond number, a bubble first appears in a single form, followed by a period of double bubble behaviors, and back to a period of single form. Finally, a bubbling regime map was constructed to describe the dynamic behaviors of bubbles under the conditions of different Weber and Bond numbers.