The formation of satellite droplets by unstable binary drop collisions

Experimental investigations on the process of satellite droplet formation b y unstable binary drop collisions are presented. The experiments are carrie d out using two monodisperse streams of drops of equal size. A systematic v ariation of the parameters influencing the collisions leads to an extended version of the stability nomogram which involves the numbers of satellite d roplets formed by stretching separation after off-center collisions. The ti me scales for the formation of liquid filaments and their breakup into the satellites are measured and, in the case that a single satellite is formed, the satellite size is measured by means of a phase-Doppler anemometer. Fur thermore, a theoretical model for the breakup of cylindrical liquid filamen ts in head-on and off-center collisions is presented. The model is based on a linear stability analysis of the filament formed after the collision. Th e critical wavelength associated with the largest deformation energy is cal culated and identified with the disturbance which eventually breaks the fil ament and determines the number of satellites formed. Comparisons with expe riments by Ashgriz and Poo [J. Fluid Mech. 221, 183 (1990)] for the head-on and near-head-on cases yield agreement of the numbers of satellites formed . (C) 2001 American Institute of Physics.