【作者】 王玥；

【导师】 邓程程；

【作者基本信息】 华中科技大学 ， 动力工程及工程热物理， 2021， 硕士

【摘要】 莱顿弗罗斯特效应是一种常见的传热现象,当液体沉积在较热的固体表面上,液体迅速沸腾,并在液体和基底之间形成一层蒸汽层。这层蒸汽层不仅会阻碍基底和液体之间的传热,也会减小基底和液体之间的阻力,这种现象称为莱顿弗罗斯特现象。莱顿弗罗斯特现象被广泛的应用,如用于自推进液体、冷却、减阻等。在过去的几十年中,尽管人们在宏观尺度上对莱顿弗罗斯特效应进行了较多的研究,但在纳米尺度对莱顿弗罗斯特效应的认知仍然有限。因此,有必要在纳米尺度上深入研究莱顿弗罗斯特效应,并揭示纳米尺度与宏观尺度之间现象差异的不同机制。本文通过分子动力学模拟研究了不同亲疏水性基底对纳米水膜莱顿弗罗斯特温度点的影响规律,并阐明了与宏观尺度不同的作用机理。提出了一种动态密度监测法,通过分子动力学模拟准确获取在不同亲疏水表面的莱顿弗罗斯特温度点。研究结果表明,在纳米尺度的莱顿弗罗斯特温度点随着基底的疏水性增加呈现出先下降后上升的趋势,这与宏观尺度随着疏水性增加单调下降的趋势不同。通过分析基底与纳米水膜之间的粘附力和界面热阻的竞争机制,以及液体的重力在纳米尺度和宏观尺度对莱顿弗罗斯特效应的不同贡献,揭示了引起这种现象差异的机理。此外,还研究了纳米水膜和纳米水滴在相同基底上出现莱顿弗罗斯特效应的差异,发现在相同亲疏水性基底表面纳米水滴的莱顿弗罗斯特温度点比纳米水膜低,这是由于纳米水滴与基底之间的粘附力小于纳米水膜所导致的。本文的研究工作不仅有助于加深对纳米尺度的莱顿弗罗斯特现象机制的理解,而且为莱顿弗罗斯特效应的相关应用提供参考指导,包括设计抗阻力表面、自推进液滴、自组装纳米结构和热管理应用等。更多还原

【Abstract】 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.更多还原