The Effect of Nano-Tailored Surfaces on Steam Condensation

Abstract

Hydrophobic coatings have been created through self-assembled mono layers (SAMs) on copper alloy (99.9% Cu, 0.1% P) surfaces to enhance steam condensation through dropwise condensation. The use of self-assembled monolayers (SAMs) facilitates the deposition of desirable films that are only as thick as the composite molecules are long. A polished copper alloy surface is oxidized to copper oxide on treatment with the hydrogen peroxide solution and the oxidized copper surface is reduced by the n-octadecyl mercaptan solution to form the ultra thin organic film. Stearic acid solution was also used to form an ultra thin organic film on the surface. In general, a SAM system with a long-chain, hydrophobic group is nano-resistant, meaning that such a system forms a protective hydrophobic layer with negligible heat transfer resistance but a much stronger bond. When compared to complete filmwise condensation, the SAM coating increased the condensation heat transfer rate by a factor of 3 for copper alloy surfaces, under vacuum condition (33.86 kPa). Contact angle measurements are used to pre-determine the condensation mode for the SAM coated surfaces. Lifetime of maintaining dropwise condensation is greatly dependent on the processing conditions.Copyright © 2003 by ASME