Visualization of flash-boiling Jets at up to five million frames per second

Flash boiling of jets is important in several industrial processes, as the flash boiling offers excellent atomization characteristics when it is intentionally applied such as in some combustion systems involving fuel injection under superheated conditions. Furthermore, such jets are can be produced in high-pressure fuel leaks, where an explosive atomization and vaporization occurs spreads fine spray of droplets even far from the source. The rapid phase transition, from liquid to vapor, starts by the formation of micro-bubbles that rapidly expand and consequently break up the liquid jet. We experiment with a number of different liquids for small jet diameters in the range from 20 to 400 microns. Using ultra-high-speed video imaging at 200 ns time resolution, we observe speeds of bubble expansion as large as 140 m/s, or much faster than the jet velocity. We characterize the spray-droplet sizes, track their motions and evaluate overall spray angles which can be close to 360°.