When an upward-flowing water jet impinges on an interface with an immiscible layer oflighter oil above it, the jet momentum lifts the interface and forms a cavity. Below a threshold based on Richardson number (Ri) and Reynolds number (Re), no droplets form. Above this threshold, oil drops are formed by two Richardson numher-dependent mechanisms. At high Richardson num- ber, an oil lip created at the edge of the cavity detaches to form oil droplets in the water below. At lower Richardson number, the water cavity becomes unstable and alternately collapses and re- forms. As the collapsing cavity impacts the interface, it drags down fingers of the upper oil layer, which break into oil droplets. This article contains extensive droplet size distributions for vary- ing Richardson number and Reynolds number and discusses the effects of varying viscosity ratio m) and Morton number (Mo). Droplet sizes exhibit polydisperse log-normal distributions with mode diameters rangingfrom 0.6 to 1.5 mm. Characteristic diameters decrease primarily with increasing Re' /Ri, and to a lesser extent with decreasing viscosity ratio. Droplet distributions re- sulting.from the lip pinch-off mechanism have a larger characteristic diameter than those formed by the cavity collapse mechanism.
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