Rapid chilldown mechanism of a low thermal conductivity coating on a flat plate in a liquid nitrogen pool

Abstract

This study numerically and theoretically investigated the rapid chilldown mechanism of a low-thermal-conductivity (low-k) coating and its impact on the boiling regime transition of a flat plate in a liquid nitrogen pool. A numerical model incorporating intermittent liquid–solid (L–S) contact was developed, and it revealed that the L–S contact induces a rapid, localized temperature drop. This temperature drop was more pronounced for low-k coated surfaces than for the bare ones, resulting in a faster regime transition. Specifically, the transition was triggered when the L–S contact region locally reaches the minimum heat flux temperature, with thicker plates and thinner coatings requiring a longer regime transition times. Notably, the numerical calculations indicated that the optimal coating thickness for minimizing the chilldown time is 170 µm, regardless of stainless-steel plate thickness. To theoretically reveal the mechanism behind the fast regime transition induced by the low-k coating, a closed-form expression for predicting the regime transition time was derived, identifying four nondimensional parameters that govern the transition. This expression explicitly showed that regime transition is influenced not only by the thermal effusivity, conductivity, and thickness of the coating layer but also by the thermal effusivity, diffusivity, and thickness of the metal plate. Finally, this study paves the way for a systematic approach to quantify the effects of these parameters and provides a design guideline for selecting the appropriate coating thickness to regulate the chilldown time.