The Impact Of Surface Wettability On Leidenfrost Effect At Nanoscale:a Molecular Dynamics Study

Leidenfrost effect is a common heat transfer phenomenon which occurs when liquids are deposited on hot solid surfaces,the liquid boils quickly and a layer of vapor is formed between the liquid and substrate.This vapor layer not only hinders the heat transfer between the substrate and the liquid,but also reduces the drag force.Therefore,the Leidenfrost effect plays an important role in many applications including self-propelling liquid,cooling,drag reduction and so on.Over the past few decades,the Leidenfrost effect has been systematically investigated at macroscale.In spite of many investigations of the Leidenfrost effect at the macroscale,there is a limited body of knowledge about the phenomenon at the nanoscale regime.Therefore,there is a great demand for in-depth investigation of Leidenfrost effect at the nanoscale dimensions,and explore the essential mechanism of the difference between nanoscale and macroscale.In this thesis,we investigate the impact of substrate wettability on Leidenfrost point of nano-water film through molecular dynamics simulations,and elucidate the new mechanism different from that at macroscale.A method of monitoring dynamic density changes is proposed to obtain accurate Leidenfrost points under different surface wettability in molecular dynamics simulations.The results show that Leidenfrost points decreases firstly and then increases with the surface wettability at nanoscale,which is different from the monotonous trend at macroscale.The mechanism causing the difference is revealed through analyzing the competition mechanism of adhesion force and interfacial thermal resistance between substrate and nano-water film,as well as different contributions of gravity impact on Leidenfrost points at nanoscale and macroscale.In addition,this paper also analyzes the difference in the Leidenfrost points of the nanowater film and the nano-water droplets on the substrate of same wettability,and found that the Leidenfrost point of the nano-water droplets is lower than that of the nano-water film,which is due to that the adhesion between the nano-water droplets and the substrate is less than that of the nano-water film.The research work will not only help to deepen the understanding of the mechanism of the Leidenfrost effect at the nanoscale,but also provide reference guide for related applications,including the design of resistance surfaces,self-propelled droplets,selfassembled nanostructures,and thermal management,etc.