EXPERIMENTAL-STUDY OF 2 INTERACTING DROPS IN AN IMMISCIBLE FLUID

Experiments were performed in order to elucidate the effects of hydrod ynamic interactions between two drops on their gravity-induced relativ e motion. The relative trajectories of two drops, their relative veloc ities, and the travel time for them to flow around each other were mea sured for different initial horizontal separations. Two size ratios an d two viscosity ratios were investigated. Hydrodynamic interactions si gnificantly reduce the relative velocity of two nearby drops and cause them to flow around each other with curved trajectories, resulting in a longer duration of the close encounter, compared with that for two non-interacting drops. These effects increase with decreasing drop sep aration, decreasing size ratio, and increasing viscosity ratio. Experi mental results are in good agreement with theoretical predictions, exc ept when the drops become sufficiently close that interface deformatio n occurs.