Annals of the Assembly for International Heat Transfer Conference 13

ISBN 1-56700-225-0 / CD 1-56700-226-9

Year 2006

T. Liu
Dalian University of Technology, Dalian, China

C. Mu
Dalian University of Technology, Dalian, China

X. Sun
Dalian University of Technology, Dalian, China

S. Xia
Dalian University of Technology, Dalian, China

The mechanism of the formation of initial condensate droplets for dropwise condensation is still in suspense. To solve the problem, we must understand if the initial condensation is in nucleus or in thin film in nanometer scale, since the calculation of the thermodynamics for new phase formation indicates that the size of the condensate nucleus is in nano-scale. Magnesium was applied as condensation surface in this study since it can react with hot water (condensate) and thus makes the chemical compositions of the surface changed. In the experiments, the initial condensation of steam on the magnesium surfaces was achieved in the designed apparatus by controlling the subcooling and the condensation time. Then, the test surfaces were scanned on an electron probe microanalyzer (EPMA) for the variation of the chemical compositions on the surfaces before and after the initial condensation, which can be used to deduce the state of the initial formed condensate, whether in nuclei or in thin film. The results showed that the oxygen contents on the test surfaces increased with subcooling and condensation time obviously after the initial condensation. And the oxygen on the test surface distributed non-uniformly. These consequences indicate that the initial condensate forms in the nucleus state on solid surfaces, not in the state of thin film. Therefore, the mechanism of formation of initial liquid drops for dropwise condensation accords with the hypothesis of surface nucleation sites.

CSN-06 pages DOI: 10.1615/IHTC13.p25.60 Download article

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