Passive Anti-flooding Superhydrophobic Surfaces.

Superhydrophobic (SHPo) surfaces can provide high condensation heat transfer due to the facilitated droplet removal. However, such high performance has been limited to low supersaturation conditions due to the surface flooding. Here we quantify the flooding resistance defined as the rate of increase in the fraction of water-filled cavities with respect to the supersaturation level. Based on the quantitative understanding of the surface flooding, we suggest the effective anti-flooding strategies through tailoring nanoscale coating heterogeneity and structure length scale. Experimental verification is conducted using CuO nanostructures having different length scale combined with hydrophobic coatings with different nanoscale heterogeneities. The proposed anti-flooding SHPo can provide ~130% enhanced average heat transfer coefficient with ~14% larger supersaturation range for droplet jumping compared to the previous CuO SHPo. The proposed anti-flooding parameter and the scalable SHPo will help develop high performance condensers for real world applications operating at a wide range of supersaturation levels.