超撥水面における凝縮熱伝達 Condensation Heat Transfer on a Super Hydrophobic Surface
Condensation heat transfer technologies are applied to heat pump systems, heat pipes etc. Dropwise condensation heat transfer coefficient is about 20 times in Filmwise condensation heat transfer coefficient as large. A possibility that it improves further by using super hydrophobic surface is expected. Then, in the purposeof investigating condensation heat transfer characteristics on a super hydrophobic surface, experiments had been carried out. Super hydrophobic surfaces are made by coating PTFE (polytetrafluoroethylene), using Alkyl Ketene Dimers or plating etc. The coating PTFE was used at this study. Also, a hydrophilic surface was used to compare with the super hydrophobic surface.Super hydrophobic and hydrophilic treatment were done at 40 mm × 40 mm area of a metal plate.Experiments were carried out with pure water in pressure of 101 kPa and steady condition. The circulating water flow was 200 liter per hour. Atmosphere in a vessel was pure steam or steam including air. The condensation surface was stood vertical direction. Temperatures were measured vertical and horizontal direction by thermocouples. Heat flux and temperature of cooling surface was calculated by the horizontal temperature distribution.The results were obtained as follows. The super hydrophobic surface did not have a large condensation heat transfer coefficient. The super hydrophobic nature appears with a fractal micro structure and existing -CF_3. But, the super hydrophobic nature was lost by filling with water condensate of steam in the fractal micro structure.