Droplet formation and size distributions from an immiscible interface impinged with a vertical negatively buoyant jet

When upward-flowing water jet impinges on an interface with an immiscible l ayer of lighter oil above it. the jet momentum lifts the interface and form s a cavity. Below a threshold based on Richardson number (Ri) and Reynolds number (Re), no droplets form. Above this threshold, oil drops are formed t wo Richardson number-dependent mechanisms. At high Richardson number, an oi l lip created at the edge of the cavity detaches to form oil droplets in th e looter below. At lower Richardson number, the water cavity becomes unstab le and alternately collapses and reforms. As the collapsing cavity impacts the interface, it drags down fingers of the upper oil layer, which break in to oil droplets. This article contains extensive droplet size distributions for varying Richardson number and Reynolds number and discusses the effect s of varying viscosity ratio (eta) and Morton number (Mo). Droplet sizes ex hibit polydisperse log-normal distributions with mode diameters ranging fro m 0.6 to 1.5 mm. Characteristic diameters decrease primarily with increasin g Re-3/Ri, and to a lesser extent with decreasing viscosity ratio. Droplet distributions resulting front the lip pinch-off mechanism have a larger cha racteristic diameter than those formed by the cavity collapse mechanism.