Two dimensional liquid flow focusing

Abstract

Flow focusing of liquid in a gaseous medium is typically axisymmetric, and it is based on a round capillary positioned on top of a circular aperture, which restricts the gaseous flow from forming a pressure drop that accelerates the liquid into a fine jet. We report an experimental study on the two dimensional flow focusing enabled by a wedge over a slit that provides similar gas flow restriction. As the wedge-to-slit distance is gradually reduced, the liquid dripping transforms into a single continuous jet that then splits into two, three, and more approximately equally-spaced jets. Below a critical wedge-to-slit separation, the liquid undergoes random atomization. The complete set of phenomena is rationalized by the dispersion relation that suggests that the jet spacing is inversely proportional to the square root of the local pressure gradient of the gas flow field. Typical experiments in the incompressible gaseous flow regime can achieve the jet spacing as short as ∼100 µm at the pressure gradient maxima.