Experimental investigation on bubble coalescence regimes under non-uniform electric field

Abstract

In this study, the characteristics of interactions between bubbles in ethanol were examined using a needle-ring electrode rig in the presence of a direct current electric field, using high-speed photography and with a focus on the effect of the electric field strength on the bubble coalescence. The results show bubble coalescence associated with four regimes in the manipulated parameter regions-namely, the coalescence of growing bubbles, single coalescence of rising bubbles, secondary coalescence of rising bubbles, and multiple coalescences of bubbles. The bubble interaction dynamics-which are characterized by the bubble trajectories, height positions, inclination angles, and bubble sizes-show that the bubble approach, collision, and coalescence in the electric field proceed in ways different from those reported in the literature. Furthermore, the cross-sectional average bubble diameter values corresponded to the bubble coalescence regimes. In addition, the increase in the Weber number (We) and electrical Bond number (BoE) gives rise to the bubble coalescence frequency. The We works to strengthen the wake induction, while the BoE works to accelerate the generation of smaller bubbles.