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Coalescence-induced nanodroplet jumping

Hyeongyun Cha1,2, Chenyu Xu1, Jesus Sotelo1, Jae Min Chun1, Yukihiro Yokoyama1, Ryan Enright3, and Nenad Miljkovic1,2,*

  • 1Department of Mechanical Science and Engineering, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, USA
  • 2International Institute for Carbon Neutral Energy Research, Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka 819-0395, Japan
  • 3Thermal Management Research Group, Efficient Energy Transfer Department, Bell Laboratories Ireland, Nokia, Blanchardstown Business & Technology Park, Snugborough Road, Dublin 15, Ireland

  • *Corresponding author: nmiljkov@illinois.edu
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Phys. Rev. Fluids 1, 064102 – Published 14 October, 2016

DOI: https://doi.org/10.1103/PhysRevFluids.1.064102

Abstract

Water vapor condensation on superhydrophobic surfaces has received much attention in recent years due to the ability of such surfaces to shed microscale water droplets via coalescence-induced droplet jumping, resulting in heat transfer, anti-icing, and self-cleaning performance enhancement. Here we report the coalescence-induced removal of water nanodroplets (R≈500nm) from superhydrophobic carbon nanotube (CNT) surfaces. The two-droplet coalescence time is measured for varying droplet Ohnesorge numbers, confirming that coalescence prior to jumping is governed by capillary-inertial dynamics. By varying the conformal hydrophobic coating thickness on the CNT surface, the minimum jumping droplet radius is shown to increase with increasing solid fraction and decreasing apparent advancing contact angle, allowing us to explore both hydrodynamic limitations stemming from viscous dissipation and surface adhesion limitations. We find that, even for the smallest nanostructure length scale (≤100 nm) and lowest surface adhesions, nonideal surface interactions and the evolved droplet morphology play defining roles in limiting the minimum size for jumping on real surfaces. The outcomes of this work demonstrate the ability to passively shed nanometric water droplets, which has the potential to further increase the efficiency of systems that can harness jumping droplets for a wide range of energy and water applications.

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Phys. Rev. Fluids 1, 064102– Published 14 October, 2016
  • Received 26 February 2016
Article part of CHORUS

©2016 American Physical Society

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