Experimental and theoretical investigation of the Leidenfrost dynamics of solid carbon dioxide discs sublimating on a solid substrate

Volatile liquid droplets levitate on a cushion of their vapor when placed on a hot solid substrate. While extensive research has focused on investigating this phenomenon, commonly known as the Leidenfrost effect in the context of liquids, it may also occur for solids whose triple point pressure is above normal ambient conditions. The present study experimentally and theoretically investigates the Leidenfrost effect for a disc-shaped dry ice pellet placed on a temperature-controlled hot sapphire substrate. The spatial and temporal evolution of the vapor layer thickness below the pellet is measured for varying substrate temperatures using optical coherence tomography (OCT). Simultaneously, the shrinkage of the sublimating dry ice pellet is recorded using video cameras. It is shown that the bottom surface of the pellet is approximately flat within the surface roughness and the resolution of the experimental setup. Intriguingly, this study reveals that the vapor layer thickness below a Leidenfrost solid increases with time in contrast to the dynamics observed for a Leidenfrost liquid droplet/puddle. Additionally, a theoretical model based on the lubrication approximation is employed to estimate the vapor layer thickness and the temporal evolution of the pellet's geometry. The theoretical predictions generally agree well with the measurements throughout the majority of the pellet's lifespan, with deviations observed towards the end of its sublimation due to the assumption of a constant pellet diameter in the model. Furthermore, the theoretical predictions reasonably represent the pellet's lifetime across a wide range of substrate temperatures, validating the predictive capabilities of the theoretical model in the present scenario.