Modeling the Effect of the Leidenfrost Vapor Coat Behavior on the Vitrification in Micro-Droplets Using the Cryogenic Droplet Levitation Time

Abstract

The levitation (“hovering”) of a liquid droplet on the surface of the coolant such as liquid nitrogen (LN2) is a useful model for studying the Leidenfrost effecr (LFE), that is formation of a vapor film of boiling coolant around the surface of a relative,ly hotter sample, at cryogenic temperatures. Several models of the cryogenic droplet levitation (CDL) have been proposed but no experimental verifications had been proposed for this model in earlier papers. Utkan Demirci’s group has recently developed fast ice-free cooling (vitrification) of microdroplets formed by an ink-jet printer. The group proposed a combination of a theoretical model of film boiling on a hot sphere with the zone theory of non-isothermal kinetic ice propagation within an initially liquid levitating droplet, and they gave theoretical predictions and experimental evaluations of the CDL (Leidenfrost) time tLF of droplets hovering on the surface of LN2 [6]. Here, we report our own experiment results of verification of the data and predictions reported in [6] and describe a thermodynamical model that for elucidating the fate of the levitating droplets. This model adequately explains our experimental results on measuring tLF but almost predicts somewhat 4-fold departure from the numbers claimed by Demirci’s group. We also discuss possible flaws of the model and, especially, experimental claims presented in [6].