关键词: 粗糙度, 化学成分异质性, 滴状冷凝, 接触角, 润湿性

Abstract: Visual experiments were employed to investigate wettability and heat transfer characteristics of steam condensation on vertical copper plates with different surface roughness by grinding.Effects of surface roughness and oxidation-induced chemical inhomogeneity on wettability and heat transfer characteristics of steam condensation were analyzed.The results indicate that the contact angle increases to a maximum value when the surface roughness reaches 0.15 μm and then decreases with increasing surface roughness.Moreover,chemical inhomogeneity induced by oxidation during steam condensation on the modified surface always contributes to enlarge contact angle and thus increase hydrophobic property.The results suggest that the wettability and steam condensation mode on the copper surface are determined by micro-scale surface roughness and chemical inhomogeneity.The experimental results show that the oxidized surface with surface roughness of about 0.15 μm exhibits complete dropwise condensation,increasing condensation heat transfer coefficient by a factor of 3.5 compared to complete filmwise condensation,but a surface with larger roughness will inhibit the drops to depart from the condensing surface and hence reduce the condensation heat transfer coefficient,so that the condensation heat transfer of the surface with roughness of 0.09 μm is larger than that with surface roughness of 0.15 μm.

Key words: roughness, chemical inhomogeneity, dropwise condensation, contact angle, wettability