The Leidenfrost effect is at once familiar and mysterious. The heart of the effect is easy enough to observe and understand: Sprinkle a liquid on a hot surface and the drops skitter around frictionlessly, levitated by a thin cushion of their own vapor. Although the drops evaporate eventually, the insulation of the vapor keeps them liquid for tens of seconds or more.
Beyond that simple picture, it gets a lot more complicated. The aerodynamics of the vapor, hydrodynamics of the liquid, and continual flux of heat and mass between the two phases are all tremendously difficult to understand in detail, and a number of seemingly elementary questions remain unanswered. In particular, there’s little physical understanding of what determines the Leidenfrost point—the minimum surface temperature, typically many tens of degrees above a liquid’s boiling point, required for the drop to levitate.
The richness of Leidenfrost physics, combined with the absence of...
