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.

摘要：

通过紫铜基表面上制备两种具有微纳米结构的超疏水表面以及相同化学修饰的光滑疏水表面，实验研究了各表面上空气环境下水的润湿特性以及在纯蒸汽、蒸汽-空气混合气体环境下，表面的滴状冷凝传热特性和冷凝液滴的运动和润湿特性。结果表明：纯蒸汽滴状冷凝条件下，超疏水表面的传热性能明显低于光滑疏水表面的传热性能；含低浓度不凝气蒸汽冷凝环境下，超疏水表面传热性能与光滑疏水表面相近；蒸汽冷凝环境中，超疏水表面上液滴的接触角明显低于其在空气条件下接触角，并且接触角滞后增大。分析得到，微纳米结构的存在使冷凝过程液滴的接触角滞后增大，微纳米结构中冷凝液滞留增加的壁面热阻等抑制了滴状冷凝传热性能；并提出了蒸汽及含不凝气蒸汽冷凝环境中液滴在超疏水表面上的润湿模式。