Pu Jin Huan, Wang Si Kun, Sun Jie, Wang Wen, Wang Hua Sheng
School of Engineering and Materials Science, Queen Mary University of London, London E1 4NS, United Kingdom.
School of Chemical Engineering and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China.
Langmuir. 2021 Mar 30;37(12):3731-3739. doi: 10.1021/acs.langmuir.1c00236. Epub 2021 Mar 17.
Molecular dynamics simulations were conducted to systematically investigate how to maintain and enhance nanofilm pure evaporation on nanopillar surfaces. First, the dynamics of the evaporation meniscus and the onset and evolution of nanobubbles on nanopillar surfaces were characterized. The meniscus can be pinned at the top surface of the nanopillars during evaporation for perfectly wetting fluid. The curvature of the meniscus close to nanopillars varies dramatically. Nanobubbles do not originate from the solid surface, where there is an ultrathin nonevaporation film due to strong solid-fluid interaction, but originate and evolve from the corner of nanopillars, where there is a quick increase in potential energy of the fluid. Second, according to a parametric study, the smaller pitch between nanopillars () and larger diameter of nanopillars () are found to enhance evaporation but also raise the possibility of boiling, whereas the smaller height of nanopillars () is found to enhance evaporation and suppress boiling. Finally, it is revealed that the nanofilm thickness should be maintained beyond a threshold, which is 20 Å in this work, to avoid the suppression effect of disjoining pressure on evaporation. Moreover, it is revealed that whether the evaporative heat transfer is enhanced on the nanopillar surface compared with the smooth surface is also affected by the nanofilm thickness. The value of nanofilm thickness should be determined by the competition between the suppression effect on evaporation due to the decrease in the volume of supplied fluid and the existence of capillary pressure and the enhancement effect on evaporation due to the increase in the heating area. Our work serves as the guidelines to achieve stable and efficient nanofilm pure evaporative heat transfer on nanopillar surfaces.
进行了分子动力学模拟，以系统地研究如何在纳米柱表面维持和增强纳米薄膜的纯蒸发。首先，对蒸发弯月面的动力学以及纳米柱表面纳米气泡的产生和演变进行了表征。对于完全润湿的流体，在蒸发过程中弯月面可以固定在纳米柱的顶表面。靠近纳米柱的弯月面曲率变化很大。纳米气泡并非起源于固体表面，由于强烈的固液相互作用，固体表面存在超薄的非蒸发膜，而是起源于纳米柱的角落并在那里演变，在该角落流体的势能会迅速增加。其次，根据参数研究发现，纳米柱之间较小的间距（）和较大的纳米柱直径（）会增强蒸发，但也会增加沸腾的可能性，而较小的纳米柱高度（）则会增强蒸发并抑制沸腾。最后，研究表明纳米薄膜厚度应保持在一个阈值以上，在本工作中该阈值为20 Å，以避免分离压力对蒸发的抑制作用。此外，研究还表明，与光滑表面相比，纳米柱表面的蒸发传热是否增强也受纳米薄膜厚度的影响。纳米薄膜厚度的值应由供应流体体积减小导致的对蒸发的抑制作用与毛细压力的存在之间的竞争以及加热面积增加对蒸发的增强作用来确定。我们的工作为在纳米柱表面实现稳定且高效的纳米薄膜纯蒸发传热提供了指导方针。
