Interdroplet freezing wave propagation of condensation frosting on micropillar patterned superhydrophobic surfaces of varying pitches

Freezing wave propagation among condensed droplets plays an important role in determining ice invasion and subsequent frost growth during condensation frosting processes. Many researchers have shown the use of superhydrophobic surfaces with nanoscale or hierarchical roughness for retarding interdroplet freezing wave propagation. Here we report effective reduction of interdroplet freezing wave propagation by using micropillar patterned superhydrophobic surfaces with emphasis on pillar pitch effect. Systematic experiments were carried out to examine the dependence of the freezing wave propagation velocity and the ice coverage ratio on pillar pitch. We found that given a pillar diameter there is a critical value for pillar pitch where the minimum freezing wave propagation velocity and ice coverage ratio occur. Our results also showed that compared to the smooth hydrophilic/hydrophobic surfaces, with proper pillar pitches the freezing propagation velocity can be reduced by more than one order of magnitude and the ice coverage can be reduced to 1/3. Additionally, our experimental findings revealed three distinctive physical mechanisms/modes. A quantitative mapping of three regimes was obtained to elucidate the significant effects of pillar pitch on interdroplet freezing wave propagation on superhydrophobic substrates with patterned micropillars. (C) 2017 Elsevier Ltd. All rights reserved.