Bubble formation from sub-millimeter orifices under variable gas flow conditions

We provide an experimental investigation on the mechanism of the bubble formation from sub-millimeter orifices under variable gas flow conditions VGFC. The effect of influential parameters including the volumetric gas flow rate Q, the orifice diameter d(or), and the volume of the gas reservoir V-c upstream of the orifice are investigated in detail. We found that, by enlarging V-c; q increases. This affects various aspects of bubble formation dynamics such as the bubble base expansion, the apparent contact angle at the three-phase contact point, and the bubble detachment criterion. The effect of V-c is best presented by its dimensionless group, the capacitance number N-c. The minimum N-c from which the influence of the gas reservoir becomes important depends on the orifice size. Moreover, a significant increase in V-c leads to a change in the bubbling regime towards multiple bubble formation. (C) 2021 Elsevier Ltd. All rights reserved.