Passive Anti-Flooding Superhydrophobic Surfaces

Abstract

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

Rapid and Persistent Suction Condensation on Hydrophilic Surfaces for High-Efficiency Water Collection

“…Moreover, because the confinement effect of the holes becomes stronger when S / R decreases, the deviation in the shedding radius of droplets gets smaller, indicating a better regulation of the droplet shedding size. The maximum droplet shedding radius for RIPS with S = 75 μm is decreased down to ∼25 μm, even smaller than that for the state-of-the-art superhydrophobic surfaces with low surface energy. − Figure e shows the time evolution of the cumulative water collection weights for these five samples. As shown, the cumulative weight of condensate on RIPS exhibits a perfect linear relationship versus time, indicating that the suction condensation is stable without deterioration.…”

Advances in Dropwise Condensation: Dancing Droplets

“…To delay the occurrence of flooding for achieving stable jumping droplets, various superhydrophobic surfaces with closely spaced nanostructures (Figure 9a) have been recently proposed to spatially control nucleation [66,98,99]. Minimizing the spacings using high-aspect ratio nanowires can promote to obtain a vapor density difference between the inside and outside of the nanoscale spacing.…”

Effect of Surface Structure Complexity on Interfacial Droplet Behavior of Superhydrophobic Titanium Surfaces for Robust Dropwise Condensation

“…When the degree of supersaturation increases, the superhydrophobicity becomes unstable, causing any improvements to the condensation heat exchange performance to be lost [ 30 , 31 , 32 , 33 ]. In order to address this issue, several studies have explored techniques to control the degree of supersaturation so that superhydrophobicity can be maintained [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ].…”