Mercredi 5 Février à 10 h 30 Amphithéâtre Nougaro
When a liquid droplet is placed on a very hot solid, it levitates its own vapor layer ; a phenomenon commonly called the Leidenfrost effect. Although the mechanisms governing the droplet’s levitation have been explored, not much is known about the fate of the evaporating Leidenfrost droplet. We study the final stages of evaporation of Leidenfrost droplets. While initially small Leidenfrost droplets tend to take off and disappear, surprisingly, the initially large ones explode with a crack sound. We interpret these in the context of unavoidable droplet contaminations : as the droplet evaporates, the contaminants accumulate at the droplet-air interface, resulting in reduced evaporation rate and finally, contact with the substrate. We validate this hypothesis by introducing controlled amounts of (microparticle) contaminants within the droplet, and reveal a universal 1/3 scaling law for the dimensionless explosion radius as a function of contaminant fraction. Our findings open up new opportunities for controlling the duration and rate of Leidenfrost heat transfer and propulsion, by tuning the droplet’s size and contamination.