Effects of surface free energy and nanostructures on dropwise condensation
Effects of surface free energy and nanostructures on dropwise condensation
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DOI：
10.1016/j.cej.2009.04.007
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发表时间：
2010-02-01
影响因子：
15.1
通讯作者：
Li Xiaonan
中科院分区：
文献类型：
--
作者：
Lan Zhong;Ma Xuehu;Li Xiaonan
实验研究了表面自由能和纳米结构对滴状冷凝的影响。采用氧化法和刻蚀法在铜基底上制备了纳米结构。在镜面抛光铜基底（SAM-2）和纳米结构铜基底（SAM-1）上制备了十八烷基十八烷基十八烷自组装膜，以促进DWC。实验数据表明，与镜面抛光的SAM-2相比，纳米结构表面SAM-1并没有改善滴状冷凝传热性能，以至于预期增加可能的冷凝表面积。这可能是由于纳米结构对冷凝膜的延迟。然而，表面自由能和冷凝表面的纳米结构的结合效应被发现在冷凝传热强化中起着非常重要的作用。在冷凝过程中，SAM-1表面的分形结构和空洞被冷凝物填充，形成了冷凝物和铜区域的复合冷凝表面。因此，该复合冷凝表面的平均表面自由能大于SAM-2表面。SAM-1的冷凝液与冷凝表面之间的表面自由能差小于SAM-2的冷凝液与冷凝表面之间的表面自由能差，传热系数也小于SAM-2。SAM-2表面的凝结换热增强了3倍，这是由于凝结水与凝结表面之间的表面自由能差增大所致。(C)2009爱思唯尔有限公司版权所有。
Effects of surface free energy and nanostructures on dropwise condensation (DWC) were investigated experimentally. The oxidation and etching methods were applied to prepare the nanostructures on the copper substrates. Self-assembled monolayers coatings of n-octadecyl mercaptan were prepared on mirror-polished (SAM-2) and the nanostructured (SAM-1) copper substrates to promote the DWC. Experimental data presented that the nanostructure surface SAM-1 did not improve the dropwise condensation heat-transfer performance so much as to be expected for increasing the possible condensing surface area, compared to the mirror-polished SAM-2. This may be caused from the nanostructure's retardance to the condensate film. However, the incorporating effects of surface free energy and nanostructures of the condensing surface were found to play a really important role in the condensation heat-transfer enhancement. The fractal-like structures and the voids on SAM-1 surface were filled with condensate in the condensing process which resulted in a composite condensing surface of condensate and copper regions. Thus the average surface free energy of this composite condensing surface is larger than that of SAM-2 surface. The surface free energy difference between the condensate and the condensing surface of SAM-1 is less than that of SAM-2, so are the heat-transfer coefficients. The condensation heat-transfer is enhanced by a factor of 3 for SAM-2 surface, due to an increase of surface free energy difference between the condensate and condensing surface. (C) 2009 Elsevier B.V. All rights reserved.