On the coalescence speed of bubbles

Two bubbles brought into contact will coalesce rapidly. We study experimentally the initial coalescence motions in the neck region connecting the two bubbles, using an ultrahigh-speed video camera. The air bubbles are grown in ethyl alcohol, at the ends of two opposing vertical needles, until they come into contact. The growth rate of the neck is measured and modeled with a capillary/inertial balance. The instantaneous profile in the neck forms a circular arc, with the ratio of the two principal radii of curvatures increasing linearly in time. (c) 2005 American Institute of Physics.