Determination of the Mechanism of Droplets Post-impact Atomisation in Water Sprays at Temperatures Bellow the Critical Nukiyama and Leidenfrost Values

Abstract

Several non-intrusive laser diagnostic techniques (PIV, Marker Nephelometry and PLIF) were applied to study spray impact morphology: droplets velocity and size prior and after the impact, the number of droplets in the impact and post-impact zones, and the presence of vorticity fields in the impact area, at a temperature lower than the critical Nukiyama and Leidenfrost temperatures. The experimental results suggest that the process of droplet post-impact atomisation follows a hydrodynamic mechanism in which the first droplets that hit the wall form a liquid film. Later, the film breaks up because of the impact of the next incident dropletsm.  As a result, a small number of relatively large post-impact droplets of low velocity is formed and pushed away from the zone of impact.