Visualization of bubble detachment and coalescence under the influence of a nonuniform electric field

Abstract

The effect of a nonuniform electric field on the formation, coalescence and detachment of single bubbles and pairs of air bubbles injected into a stagnant, isothermal liquid through orifices is studied to identify characteristic bubble behavior patterns. The results of the experimental visualization clearly indicate the significant differences in bubble shape, size and trajectory caused by the electric field. The electric field was applied between a flat, circular and horizontal ground electrode and a spherical, off-axis top electrode. In single bubble experiments the bubble was tilted towards or away from the upper electrode under the influence of the electric field. Although the direction of the tilt alternated (even in a single experiment), in the majority of the cases the bubble trajectory tilted towards the top electrode. In bubble pair experiments the bubbles behaved similarly to the single bubble case at larger volume flow rates. In low volume flow rate experiments the bubbles were tilted away from each other. Furthermore, the detachment frequency increased under the influence of the electric field, which indicates decreased bubble volume for lower volume flow rates. The effect of the electric field on vertical and lateral bubble coalescence was analyzed and quantified in terms of the detachment time.