Leidenfrost solid sublimating on a superheated solid substrate

Sublimating solids when placed on a hot substrate levitate on the cushion of their own vapor. Here we study this so-called Leidenfrost effect for solid carbon dioxide (dry ice) placed on a temperature controlled sapphire substrate. Temporal evolution of the vapor layer thickness between the substrate and dry ice pellet, and the geometric parameters of the latter are captured by an optical system. We observe that the vapor layer thickness for a cylindrical dry ice pellet increases with time as opposed to a volatile puddle of liquid under similar situation. This behavior is also theoretically studied by employing energy and momentum balance under the assumptions of lubrication approximation, uniform vapor layer thickness, and constant pellet diameter. A comparison between the model predictions and experimental data for vapor layer thickness and the pellet height reveal good agreement.