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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-474-8

ISBN Online: 978-1-56700-473-1

International Heat Transfer Conference 16
August, 10-15, 2018, Beijing, China

A VISUALIZED STUDY OF CONDENSATION HEAT TRANSFER OVER A HORIZONTAL CIRCULAR TUBE WITH A MICROPOROUS HYDROPHOBIC SURFACE

Get access (open in a dialog) DOI: 10.1615/IHTC16.cod.022417
pages 2155-2163

Sinopsis

The condensation of water vapor over a horizontal circular tube with a microporous hydrophobic surface was studied experimentally. The microporous surface having a pore diameter at nearly 20 µm was fabricated on a smooth copper tube by electrochemical deposition and then the surface hydrophobicity was realized by deposition of silane. Smooth hydrophobic and hydrophilic surfaces were also prepared and tested as reference surfaces. Condensation experiments with pure water vapor were carried out on these surfaces in a vacuum chamber maintained at a pressure of 5 kPa, and the degree of subcooling was varied from 8 to 30 °C. On the smooth hydrophilic surface, stable filmwise condensation was observed and the heat transfer coefficient was found to agree well with the classical Nusselt model. The enhancement of the heat transfer coefficient by a factor of 80% was realized on the microporous hydropholic surface, in relative to that on the smooth hydrophilic surface. This enhancement is likely due to the reduced thickness of the condensate film on the microporous hydrophobic surface. However, the tested microporous hydrophobic surface was also shown to impede the movement of condensed droplets, finally leading to a transition from dropwise to filmwise condensation. Thus, the heat transfer coefficient of the microporous hydrophobic surface was found to be lower than that of the smooth hydrophobic surface, on which a stable dropwise condensation was observed.