The Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy Utilization, North China Electric Power University, Beijing, 102206, P.R. China.
Sci Rep. 2017 Jan 5;7:39932. doi: 10.1038/srep39932.
We developed a novel micro-droplet array system, which is based on the distinct three dimensional mesh screen structure and sintering and oxidation induced thermal-fluid performance. Mesh screen was sintered on a copper substrate by bonding the two components. Non-uniform residue stress is generated along weft wires, with larger stress on weft wire top location than elsewhere. Oxidation of the sintered package forms micro pits with few nanograsses on weft wire top location, due to the stress corrosion mechanism. Nanograsses grow elsewhere to show hydrophobic behavior. Thus, surface-energy-gradient weft wires are formed. Cooling the structure in a wet air environment nucleates water droplets on weft wire top location, which is more "hydrophilic" than elsewhere. Droplet size is well controlled by substrate temperature, air humidity and cooling time. Because warp wires do not contact copper substrate and there is a larger conductive thermal resistance between warp wire and weft wire, warp wires contribute less to condensation but function as supporting structure. The surface energy analysis of drops along weft wires explains why droplet array can be generated on the mesh screen piece. Because the commercial material is used, the droplet system is cost effective and can be used for large scale utilization.
我们开发了一种新颖的微滴阵列系统，它基于独特的三维网格屏幕结构和烧结及氧化诱导的热流性能。通过将两个组件粘结，在铜基底上烧结网格。沿纬丝产生不均匀的残余应力，纬丝顶部的应力比其他位置大。由于应力腐蚀机制，烧结组件的氧化会在纬丝顶部形成带有少量纳米草的微坑。纳米草在其他地方生长，表现出疏水性。因此，形成了表面能梯度的纬丝。在湿空气环境中冷却结构会在纬丝顶部形成小水滴，其比其他位置更“亲水”。通过控制基底温度、空气湿度和冷却时间，可以很好地控制液滴尺寸。由于经丝不与铜基底接触，经丝和纬丝之间存在较大的导电热阻，因此经丝对凝结的贡献较小，但起到支撑结构的作用。沿纬丝的液滴表面能分析解释了为什么可以在网格片上生成液滴阵列。由于使用了商业材料，因此该液滴系统具有成本效益，可以大规模利用。
