An experimental study of factors which promote coalescence of two colliding drops suspended in water-I

Abstract The factors which determine whether two colliding drops will coalesce or rebound have been studied experimentally for 3.4 mm dia. anisole drops in water, using an apparatus designed to permit control of drop size, impact velocity and collision angle. Analysis of high speed movies showed that for relative approach velocities of 1.9–11.2 cm/sec, the apparent drop contact time was less than 70 msec. The probability of coalescence during this short time interval was a function of the phase and amplitude of the drop oscillations at moment of contact. The results have been analyzed using a modification of the conventional Stefan-Reynolds type film thinning equation derived for rigid interfaces. This relationship, although indicating more thinning for coalescences than rebounds, fails to predict fast enough thinning rates to validate the model. Part II gives detailed derivations for a thinning model in which interfaces are free to move, and shows how the results given in Part I can be explained by film thinning.