Dropwise Condensation on a Hierarchical Nanopillar Structured Surface
Dropwise Condensation on a Hierarchical Nanopillar Structured Surface
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DOI：
10.1021/acs.langmuir.0c00950
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发表时间：
2020-09-01
期刊：
影响因子：
3.9
通讯作者：
Okamoto, Atsushi
中科院分区：
文献类型：
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作者：
Baba, Soumei;Sawada, Kenichiro;Okamoto, Atsushi
在冷凝表面进行纳米管柱结构处理以控制润湿性，并通过滴状冷凝和液滴跳跃获得高的换热系数。以退火金生成的金(Au)纳米粒子为掩模进行了改进的干法刻蚀，并进行了高深宽比纳米加工，以获得均匀的柱面和新颖的层次化柱面。将直径为20~850 nm的均匀纳米柱表面与直径为100~860 nm的厚柱与直径为20~40 nm的细柱的分级柱面混合制备。利用未涂覆的纳米管表面进行了冷凝实验，并用显微镜观察了硅(Si)表面的冷凝行为，用高速相机从侧面观察了冷凝行为。在均匀表面US-3和分级表面HS-1和HS-2上，液滴在20-50微米的尺寸范围内经常观察到跳跃，相反，当液滴尺寸增大到50微米或更大时，观察到的跳跃次数随着液滴尺寸的增大而减少。从冷凝开始到约2min，分级表面上的液滴跳跃频率高于均匀表面，尽管分级表面上的液滴形成密度不是很大。根据从侧面观察液滴的行为，我们确定了第一次跳跃是由于附着在表面的液滴的合并，随后的跳跃是由跳跃液滴重新连接时的液滴合并引起的。各矿柱表面一次跳跃发生率均较高。
Nanopillar structure processing has been performed on condensation surfaces to control wettability and achieve a high heat transfer coefficient via dropwise condensation and jumping droplets. Modified dry etching was performed using gold (Au) nanoparticles generated by annealing Au as a mask, High-aspect-ratio nanopillar processing was also performed to produce uniform pillar surfaces and novel hierarchical pillar surfaces. A uniform nanopillar surface with pillars having diameters of 20-850 nm and a hierarchical pillar surface with thick pillars having diameters ranging from 100 to 860 nm and thin pillars with diameters ranging from 20 to 40 nm were mixed and fabricated. Condensation experiments were performed using the noncoated nanopillar surfaces, and the condensation behaviors on the silicon (Si) surfaces were observed from above using a microscope and from the side using a high-speed camera. On the uniform surface US-3 and the hierarchical surfaces HS-1 and HS-2, droplet jumps were observed frequently in the droplet size range of 20-50 mu m. In contrast, as the droplet size increased to 50 mu m or more, the number of jumps observed decreased as the droplet size increased. The frequency of droplet jumps on the hierarchical surfaces from the start of condensation to approximately 2 min was higher than that on the uniform surfaces, although the density of droplet formation on the hierarchical surfaces was not relatively large. On the basis of the observation of droplet behavior from the side surface, we identified that the primary jump was due to the coalescence of droplets adhering to the surface and that the subsequent jump was caused by the droplet coalescence when the jump droplets were reattached. The primary jump occurrence rate was high on all pillar surfaces.