Icing behavior of super-cooled condensate on hydrophilic and super-hydrophobic surfaces.

The present study investigates experimentally the frosting characteristics of super-cooled condensate on hydrophilic and super-hydrophobic surfaces under various environmental conditions. In particular, the frosting mechanism related to the delay of icing is analyzed for three different surfaces, such as different equilibrium contact angles of 74° (bare copper), 135° (thin polymer layer coated copper), and 154° (SAM-coated nano-structured copper). The experiments were carried out under the well-controlled conditions with the surface temperature ranging from -4°C to -8°C, the relative humidity of 60%, and the air temperature of 24°C. During the frosting process, images of frosting behavior were obtained in situ by connecting CMOS camera. From the results, it was found that the frosting behavior was significantly affected by the surface wettability because of the variation of surface energy. In the case of a hydrophilic surface, fast freezing was observed in the early stage of the frosting process, and the frost crystals were rapidly formed on the whole surface. On the other hand, in the case of a hydrophobic surface, dropwise condensation occurred at the early cooling stage, and some condensates were still in the super-cooled state. Moreover, a small number of frozen droplets randomly formed on the surface were strongly interacted with supercooled condensates, especially causing the evaporation of the supercooled droplet which affected the frost propagation.