Adverse impact of macro-textured superhydrophobicity on contact time reduction at high Weber numbers

Abstract

Macro textured superhydrophobic surfaces are reported to be highly effective in contact time reduction and thus a potential candidate for anti-icing applications. However, we find that the macro textured superhydrophobic cylindrical surfaces have higher contact time compared to its counterpart without any macro texturing at high impact Weber numbers (We)for the various range of curvature ratios of the cylinder and aspect ratios of the macro texturing. The asymmetric spreading is aided by the preferential jetting and flow redirection results in a stable lamella in the azimuthal direction resulting in the contact time enhancement for intermediate We number regimes. The retraction velocity is also adversely influenced by the presence of ribs in these We number regimes thus resulting in enhanced residence time. However, the dynamics at the high We regimes are governed by the hole nucleation and film rupturing. The presence of ribs is found to reduce the nucleation inception and nucleation density resulting in higher contact time compared to the non-ribbed superhydrophobic surfaces. An outcome based map was developed based on the systematic experimental observations over a wide spectrum of parametric variation. Detailed analysis is presented to explain the counter-intuitive observations.