抄録
In this paper, we experimentally investigate the formation and breakup of a hollow jet issuing from a coaxial nozzle into ambient air. The hollow jet consists of an outer water jet surrounding an inner jet of argon gas. It is very unstable and ultimately breaks up into hollow drops in various patterns: (I) mixed hollow and simple drop formation, (II) single-core hollow drop formation, and (III) multi-core hollow drop formation. We focus here on the formation of pattern (II) in which the hollow jet breaks up into a water shell enclosing a single gas bubble. Careful investigation on this regime reveals two different sub-modes to generate single-core hollow drops from the final breakup of the hollow jet. In the first sub-mode, the inner gas jet breaks up into individual bubbles that are then encapsulated by an outer shell of water. However, in the second sub-mode, just after breaking up into a gas bubble, the gas jet reunites with that bubble and then breaks up again into a larger elongated gas bubble. This sequence happens within the water jet, and is followed by the breakup of the water jet to form a large water drop that encloses this single gas bubble. All of these patterns and sub-modes are mapped in the parameter space of Weber number versus gas-to-water flow rate ratio.
