-When a drop of water falls onto a hot plate, the vapor layer between the drop and the plate provides levitation and lubrication that allows the drop to skate rapidly over the surface – an effect familiar to every chef. A novel application of this phenomenon, known as the Leidenfrost effect, has shown that a hot solid sphere under free fall in liquid can travel over twice as fast as a cold sphere by maintaining a continuous, robust, thin lubricating vapor layer around the sphere (see Figure). High-speed video imaging showed that the vapor layer reduced the adhesion between the liquid and the sphere surface resulting in a smoother liquid flow pattern and dramatic reduction in hydrodynamic drag (Videos available on EPAPS). These findings complement related lubricating vapor layer technologies such as using superhydrophobic surfaces, microbubbles injection, and supercavitation in the quest for efficient energy usage and reduced carbon emission in high speed under water propulsion applications.
