Periodic and aperiodic bubbling in submerged gas-liquid jets through a micro-channel

The common phenomena of periodic and aperiodic bubbling, which were studied merely in single-phase gas jets, are discovered to exist in submerged gas-liquid jets through a micro-channel. Due to the participation of the liquid input flow which interacts with the gas phase, the periodic and aperiodic bubbling behaviors,as well as the regime transition mechanisms, are quite different from single-phase gas jets. Periodic bubbling is formed by injecting a regular Taylor flow into bulk liquid, in which a special motion of bubbles named "bubble bifurcation" is revealed. Bubbles move into the opposite orientation to the bubbles they touch because unequal contact angles make the bubbles tilt when they detach. The bifurcation process is described by the evolutions of the contact line, bubble centers, and the bifurcation point. The second bifurcation events cause the bubble branches to rotate simultaneously. The difference of periodicity between gas-liquid jets and single-phase gas jets is explained in a dimensionless form as a function of 1/St versus Fr. Aperiodic bubbling including double coalescence, triple, quadruple, and quintuple bubble formation is found to occur at lower gas velocities than single-phase gas jets because of the different mechanism of bubble detachment in which liquid rings make bubbles pitch off before necking. The effect of liquid rings on bubbling period, as well as the disturbance waves spreading over the bubble surface, is explained. Finally, the mechanisms of bubbling losing periodicity are figured out through analyzing the correspondence relationship between the evolutions of bubbling behaviors and the flow regime transitions in the micro-channel with regime boundaries well predicted by corresponding models. Published by AIP Publishing.