Experimental Investigation of Bubble Generation via Gas Injection Through Submerged Needles

The size of bubbles is a crucial parameter in gas-liquid bubbly systems, making the investigation of bubble formation essential for effective bubble size control. The authors experimentally examined bubble generation using a high-speed video camera. They comprehensively investigated the effects of needle inner diameter, needle tilt angle, surface tension coefficient, liquid-phase viscosity, and gas injection rate on the bubble departure diameter. They also analyzed the bubble neck pinch-off and inrush phenomena. The study revealed that the influence of these factors on bubble generation was complex. Among them, needle inner diameter, surface tension coefficient, and needle tilt angle exerted a greater influence on the bubble departure diameter than liquid-phase viscosity and gas injection rate. Bubble neck pinch-off was correlated with liquid-phase viscosity, while the inrush phenomenon occurred only when the needle inner diameter was extremely small. Additionally, the correlation derivation of bubble departure diameter cannot neglect the effects of viscous drag and added mass force even at low gas injection speeds.