Hits:

Indexed by:期刊论文

Date of Publication:2010-02-01

Journal:12th Asia-Pacific-Confederation-of-Chemical-Engineering (APCChE 2008)

Included Journals:SCIE、EI、CPCI-S、Scopus

Volume:156

Issue:3

Page Number:546-552

ISSN No.:1385-8947

Key Words:Dropwise condensation; Nanostructure; Surface free energy; Superhydophobicity; Self-assembled monolayers

Abstract: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.