Patten shape effects on condensation on hybrid-wetting surfaces

Hybrid-wetting surfaces are commonly used in enhancing dropwise condensation (DWC) because of provide high droplet mobility and small droplet size. The shape of the patterns plays a significant role in determining droplet departure size, frequency, and thus, heat transfer rates, which are not introduced yet. Therefore, different pattern shapes such as circle, ellipse, and diamond share the same area, gap distance, and arrangement have been developed to conduct condensation experiments on horizontal copper tubes at atmospheric pressure. Results show that condensation heat flux and heat transfer coefficient on the diamond-shaped pattern are 40% and 60% are higher than the complete DWC and outperform the other two shapes, i.e., ellipse-and circle-shaped patterns with a gap distance of 1 mm. Unfavorable bridged droplets were observed between two or more patterns on all hybrid surfaces. The bridged droplets would result in high thermal resistance and deteriorate condensation rate. We observed that bridged droplets have been effectively reduced on the diamond-shaped patterns, which should be a primary mechanism for outperforming the circular and elliptic patterns. In addition, we observed that the gap between the patterns also plays a significant role in determining droplet dynamic and heat transfer rate on all hybrid surfaces.