Condensation on Slippery Asymmetric Bumps

TL;DR

This paper investigates how the detailed topography of asymmetric bumps influences condensate growth and transport, demonstrating that specific designs with slippery coatings significantly enhance water droplet shedding and growth rates for phase change applications.

Contribution

It reveals the role of bump radius of curvature and width on condensate behavior and introduces a novel asymmetric bump design with slippery coating for improved water transport.

Findings

Five-fold increase in droplet growth rate

Order of magnitude faster droplet shedding

Enhanced water harvesting performance

Abstract

Bumps are omnipresent from human skin to the geological structures on planets, which offer distinct advantages in numerous phenomena including structural color, drag reduction, and extreme wettability. Although the topographical parameters of bumps such as radius of curvature of convex regions significantly influence various phenomena including anti-reflective structures and contact time of impacting droplets, the effect of the detailed bump topography on growth and transport of condensates have not been clearly understood. Inspired by the millimetric bumps of the Namib Desert beetle, here we report the identified role of radius of curvature and width of bumps with homogeneous surface wettability in growth rate, coalescence and transport of water droplets. Further rational design of asymmetric convex topography and synergetic combination with slippery coating simultaneously enable self-transport, leading to unseen five-fold higher growth rate and an order of magnitude faster shedding time of droplets compared to superhydrophobic surfaces. We envision that our fundamental understanding and innovative design of bumps can be applied to lead enhanced performance in various phase change applications including water harvesting.