Abstract:

Two super-hydrophobic surfaces with micro-nanostructure were prepared with n-octadecyl mercaptan self-assembled monolayers（SAMs）.The wettability and heat transfer characteristics during the condensation of steam or steam-air mixture were investigated experimentally on a vertical tube. For the condensation of pure steam，the condensation heat transfer on the super-hydrophobic surfaces with micro-nanostructure is worse than that on a smooth hydrophobic surface. In the presence of a low-concentration of noncondensable gas（NCG），the condensation effect is almost the same for the super-hydrophobic surface and smooth hydrophobic surface. During the condensation，the micro-nanostructure，an important feature for the super-hydrophobic surfaces，does not adsorb and trap air to exhibit the super-hydrophobicity. The wetting mode of solid-liquid changes from the Cassie state in the air to the wetting state during steam condensation. The contact angle hysteresis increases. The retardarce of micro-nanostructure to the condensate increases the thermal resistance. The results demonstrate that the solid-liquid wettability of micro-nanostructure significantly influences the heat transfer performance.