Bubble coalescence dynamics

Coalescence of electrolytically‐generated, 50‐ to 600– μm‐diameter gas bubbles was observed using an optical technique that employs a linear photodiode array to detect interface movement with a resolution of 10−6s. When two bubbles coalesce, the surface energy that is released causes interface velocities of 2 to 4 m/s; these are followed by large‐amplitude damped oblate–prolate oscillations. Within the viscosity range studied, the oscillation period is insensitive to the viscosity and damping is insensitive to surface tension, in agreement with a scaling analysis based on a damped harmonic oscillator. Surface waves are superimposed on the motion. Finite‐element solutions of the free‐surface, nonlinear Navier‐Stokes equations are consistent with the experiments.