两步电沉积微/纳米结构表面的滴状冷凝的热传递

摘要

冷凝是一种重要的传热机制,在发电厂、采暖、通风、空调、制冷等行业有着广泛的应用.冷凝以两种不同的模式发生,包括膜状冷凝(FWC)和滴状冷凝(DWC).在疏水和超疏水表面上发生的滴状冷凝热传递容量远高于膜状冷凝.因此,近年来对滴状冷凝进行了广泛的研究.超疏水表面具有低表面能的微纳米结构.在本研究中,采用两步电沉积法在铜表面沉积出微/纳米结构.用乙醇和1-十八硫醇溶液自组装单分子层来降低试样的表面能.结果表明,电沉积工艺具有最佳的条件.例如,当第二步电沉积时间为2000 s时,滴状冷凝的热传递量是膜状冷凝的5倍,而当第二步电沉积时间为4000 s时,滴状冷凝(DWC)与膜状冷凝(FWC)热传递几乎相同.使用XRD和SEM分析检测制备的试样表面.SEM分析显示,在试样表面上存在一些微结构,通过延长第二步电沉积时间,可以降低表面孔隙率.%Condensation is an important regime of heat transfer which has wide applications in different industries such as power plants, heating, ventilating and air conditioning, and refrigeration. Condensation occurs in two different modes including filmwise (FWC) and dropwise (DWC) condensation. DWC occurring on hydrophobic and superhydrophobic surfaces has a much higher heat transfer capacity than FWC. Therefore, wide investigations have been done to produce DWC in recent years. Superhydrophobic surfaces have micro/nano structures with low surface energy. In this study, a two-step electrodeposition process is used to produce micro/nano structures on copper specimens. The surface energy of specimens is reduced by a self-assembled monolayer using ethanol and 1-octadecanethiol solution. The results show that there is an optimum condition for electrodeposition parameters. For example, a surface prepared by 2000 s step time has 5 times greater heat transfer than FWC while a surface with 4000 s step time has nearly the same heat transfer as FWC. The surfaces of the fabricated specimens are examined using XRD and SEM analyses. The SEM analyses of the surfaces show that there are some micro-structures on the surfaces and the surface porosities are reduced by increasing the second step electrodeposition time.