Effects of hydrophobic surface treatments on dropwise condensation and freezing of water

The effects of hydrophobic coatings on the dropwise condensation process for a flat horizontal copper plate held at a temperature much lower than the surrounding air was investigated. Extensive qualitative and quantitative data were taken to describe these effects in terms of dropsize distributions, heat and mass transfer coefficients, and digital imaging of the microscopic condensing droplets in terms of various extensive properties.;Conditions of the tests were laminar flow (Reynolds numbers of 600 to 1600), condensing surface temperature of ;A condensation model was developed based on heat transfer relationships for the condensation process and the psychrometric qualities of the ambient air. The model used as inputs the surface temperature of the condensing system, the contact angle of the liquid phase in contact with the surface, the moisture content of the air stream, and air temperature, and the velocity of the air flowing over the condensing surface. Comparisons were made between the experimental results and those predicted by the model for dropsize distributions and mass of condensate on the surface. The results from the model were within ;It was found that the application of a hydrophobic coating on a surface that is to be operated at a temperature below the freezing point of water will delay the onset of ice nucleation by 15 to 35% over an uncoated surface.