2006 Volume 39 Issue 8 Pages 826-830
The prerequisite condition for maintaining dropwise condensation on a surface is that the condensing surface should have a low surface energy. In the present paper, two different techniques were employed to achieve steam dropwise condensation over a vertical copper tube at atmospheric pressure: one is self-assembled monolayers (SAMs), and the other is electroless composite plating. The use of SAMs of docosanoic acid promotes dropwise condensation. The electroless Ni–P–PTFE coatings also achieve excellent dropwise condensation. Compared with film condensation, the condensation heat transfer coefficient can be enhanced by more than one order of the magnitude on these coated surfaces. The electroless composite coating surface of high PTFE content has a higher condensation heat transfer coefficient than that of low PTFE content. The SAM surface of docosanoic acid has the lowest surface energy which leads to the lowest thermal resistance of liquid condensate, and a negligible thickness of 30 Å with a negligible additional heat transfer resistance, thus it has better heat transfer characteristics than those of the Ni–P–PTFE surfaces.
