Experimental study and numerical simulation of periodic bubble formation at submerged micron-sized nozzles with constant gas flow rate

Visualization experiments and numerical simulations were carried out to investigate the bubble dynamic behavior at the submerged micron orifice. The diameters of the orifices varied from 0.136 mm to 0.204 mm. The bubble formation process was recorded by a high-speed video camera. The detailed bubble characteristics were obtained through image processing and a following Matlab analysis. The outcomes indicate that under a low gas flow rate, the bubble grows and detaches individually, and the bubble formation progress can be differentiated into three stages: nucleation, stable growth, and necking. The differences between micron and millimeter level orifices are obvious at the initial level of bubble formation. At the micron level, the bubble is strongly influenced by capillary pressure and it causes a longer waiting time. It is also found that the bubble shape only depends on the instantaneous bubble volume and has no relation with the gas flow under a high flow rate. We observed that the coalescence bubbling regimes are different from the multi-period formation mechanism at the millimeter level. The final bubble volume demonstrates an index increasing law with the gas flow rate. Additionally, the volume-of-fluid method was used for numerical simulation of the bubble formation process. It indicates that numerical simulations can finely predict the dynamic features of bubbles against the experiments, under low gas flow rate conditions (0.95-4.83 ml/min).