Droplet Interactions with Hot Surfaces: Boiling Modes, Leidenfrost Temperature, Dynamics, and Applications.

The interaction of droplets with high-temperature solid surfaces is critical in processes like machining cooling and internal combustion engine operations. As surface temperature rises, droplets transition through distinct boiling regimes: film evaporation, contact boiling, transition boiling, and film boiling. In the film boiling regime, droplets are suspended on a vapor layer formed by their evaporation, known as the Leidenfrost effect, which occurs above the Leidenfrost point-the minimum temperature for this phenomenon. While the vapors layer impairs heat transfer by acting as an insulator, it also facilitates droplet mobility, enabling applications in fluid motion control and driving research interest in this area. This review provides a comprehensive overview of droplet interactions with heated surfaces. It begins with a classification of boiling regimes and the criteria defining them, followed by an analysis of factors influencing the Leidenfrost point, including surface properties, liquid characteristics, and external conditions. The motion behaviors of droplets on high-temperature structured surfaces such as horizontal transport, vertical detachment, and rotation are then explored. Finally, potential applications for controlling droplet behavior on hot surfaces are discussed, including enhanced heat transfer, self-cleaning, drag reduction, and energy conversion, while highlighting emerging directions for future research.