1. Experiments on Drop Coalescence in Liquid/Liquid Systems
Ellen K. Longmire and Jungyong Kim
Department of Aerospace Engineering and Mechanics, University of Minnesota
Collisions between pairs of water/glycerin drops in silicone oil were investigated by varying initial injection angles to control the eventual collision angles. Simultaneous dual-field PIV measurements were obtained in index-matched fluids to characterize coalescence and rebounding behavior. The larger field captured trajectories, and the smaller field captured the thin film region between the colliding drops. Experiments were performed for Weber numbers [We] in the range of 1-50 and collision angles of degrees below the horizontal. The drops coalesced for We > 11 and rebounded for We < 11, and this boundary was found to be insensitive to collision angle over the range examined. Vortex ring interaction and strong drop deformation due to inertia were both found to be important precursors to coalescence. The collision angle affected the eventual location of film rupture, with the rupture location moving higher in the thin film region as the collision angle increased. The film rupture location correlated closely with the location of maximum
downward velocity in the thin film.
Rebound
We = 11,  = 34,
Coalescence
We = 22,  = 34,
Coalescence
We = 21,  = 17,
Coalescence
We = 21,  = 40,