An experimental and theoretical study on the concept of dropwise condensation
An experimental and theoretical study on the concept of dropwise condensation
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DOI：
10.1016/j.ijheatmasstransfer.2005.08.016
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发表时间：
2006-02
影响因子：
5.2
通讯作者：
S. Vemuri;K. Kim
中科院分区：
文献类型：
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作者：
S. Vemuri;K. Kim
通过在铜合金（99.9%Cu，0.1%P）表面自组装正十八烷基硬脂酸（SAM-1）和硬脂酸（SAM-2）单层膜，制备了疏水涂层，并通过滴状冷凝强化水蒸气的冷凝。在真空条件下（33.86kPa），与完全膜状冷凝相比，正十八烷基聚乙烯（SAM-1）涂层使铜合金表面的冷凝传热速率提高了3倍，在常压条件下（101 kPa），其冷凝传热速率提高了8倍。本文采用粒子数平衡的概念，导出了一个理论公式，用以预测主要由直接凝结生长的小液滴的粒径分布。该模型考虑了液滴、汽液界面的热传导等重要的传热阻力。通过已知液滴与冷凝表面的接触角和最大液滴半径，可以计算大的下落液滴的清扫效果，这也被纳入模型。在建立理论模型时，还考虑了界面换热系数对换热速率的影响。这与Le Fevre和Rose提出的大液滴的众所周知的尺寸分布相结合[E. J. Le Ferve，J.W.陈文辉，滴状冷凝传热理论，第三届国际传热会议论文集，第2卷，芝加哥，1966年，第100页。362-375），主要是通过聚结生长。我们的实验数据和目前的理论模型之间有一个令人满意的协议。
Hydrophobic coatings have been created through self-assembled mono layers (SAMs) of n-octadecyl mercaptan (SAM-1) and stearic acid (SAM-2) on copper alloy (99.9% Cu, 0.1% P) surfaces to enhance steam condensation through dropwise condensation. When compared to complete filmwise condensation, n-octadecyl mercaptan (SAM-1) coated surface increased the condensation heat transfer rate by a factor of 3 for copper alloy surfaces, under vacuum condition (33.86kPa) and to about eight times when operated under atmospheric condition (101kPa). A model using the population balance concept is used to derive a theoretical formula to predict the drop-size distribution of small drops which grow mainly by direct condensation. All the important resistances to heat transfer such as the heat conduction through the drop, vapor–liquid interface are considered in developing this model. By knowing the contact angle of the drop made with the condensing surface and the maximum drop radius the sweeping effect of large falling drops could be calculated which is also incorporated into the model. The effect of interfacial heat transfer coefficient on heat transfer rate is also considered in developing the theoretical model. This is combined with the well known size distribution for large drops proposed by Le Fevre and Rose [E.J. Le Ferve, J.W. Rose, A theory of heat transfer by dropwise condensation, in: Proceedings of 3rd International Heat Transfer Conference, vol. 2, Chicago, 1966, pp. 362–375] which grow mainly by coalescence. There has been a satisfactory agreement between our experimental data and the present theoretical model.