Leidenfrost for solids

Anyone who has sprinkled water into a hot pan has seen the Leidenfrost effect in action. A thin layer of vapor forms between the super-boiling-point surface and the droplets, causing them to levitate and skid across the pan (see Physics Today, June 2006, page 17 ). Now Nicolas Vandewalle, Stéphane Dorbolo, and Baptiste Darbois Texier at the University of Liège in Belgium have demonstrated that an analogous phenomenon can occur when solids sit atop a surface heated beyond their melting point. Using a Petri dish as a mold, the researchers created disks of water ice. They then placed a disk on a heated aluminum plate. By using a video camera to track the motion of a black foam ellipse placed atop the ice disk, the researchers were able to analyze the disk’s translation and rotation. At a range of plate temperatures between 4 °C and 35 °C Vandewalle’s team found that the ice disk moved around randomly, essentially gliding across a thin film of meltwater above the plate. To gain more control over the ice’s motion, the researchers drilled a 2 mm hole in the plate just beside the disk (see image). Water flowed along the perimeter of the disk and emptied into the hole at a rate equal to the rate of melting. The viscous drag of the ice by the flow of the meltwater stream caused the disk to rotate. The faster the ice melted, the faster the disk spun. (S. Dorbolo, N. Vandewalle, B. Darbois Texier, Phys. Fluids 28, 123601, 2016, doi:10.1063/1.4967399 .)