Leidenfrost dynamics of sublimating solid carbon dioxide disc elucidated using optical coherence tomography

Volatile liquid droplets levitate on a cushion of their vapor when placed on a hot solid substrate. So far, this so-called Leidenfrost effect has been extensively studied for liquids, but it may also occur for solids whose triple point pressure is above normal ambient conditions. This study aims to experimentally and theoretically elucidate the Leidenfrost effect for a disc-shaped dry ice pellet placed on a 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). We found that the bottom of the pellet is approximately flat within the surface roughness and the resolution of the experimental setup. We show that the vapor layer thickness below such a Leidenfrost solid increases with time in contrast to the dynamics observed for a Leidenfrost liquid droplet/puddle. Finally, the vapor layer thickness is theoretically modeled based on the lubrication approximation for the vapor flow below the pellet showing a fair agreement with the experimental results.