Session M39: Drops, Bubbles, and Interfacial Fluid Mechanics I

8:00 AM–11:00 AM, Wednesday, March 20, 2013
Room: 348

Sponsoring Unit: DFD
Chair: Sidney R. Nagel, University of Chicago

Abstract ID: BAPS.2013.MAR.M39.6

Abstract: M39.00006 : Electric Charging Effects on Condensed Droplet Jumping

9:00 AM–9:12 AM

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  Nenad Miljkovic

  Daniel J. Preston

  Ryan Enright
    (Bell Labs Ireland)

  Rong Yang

  Karen K. Gleason

  Evelyn N. Wang

When condensed droplets coalesce on a superhydrophobic surface, the resulting droplet can jump due to the conversion of surface energy into kinetic energy. This frequent out-of-plane droplet jumping has the potential to enhance condensation heat transfer. Furthermore, for more than a century, researchers have shown that droplet-surface interactions can be dominated by electrostatic charge buildup. In this work, we studied droplet jumping dynamics on nanostructured copper oxide and carbon nanotube surfaces coated with tri-chloro silane and PFDA hydrophobic coatings, respectively. Through analysis of droplet trajectories and terminal velocities under various electric fields (0 -- 50 V/cm), we show that condensation on these surfaces having both conducting and insulating substrates results in a buildup of positive surface charge (H$^{\mathrm{+}})$ due to dissociated water ion adsorption on the superhydrophobic coating. Consequently, an accumulation of the opposite charge (OH$^{\mathrm{-}})$ occurs on the condensing droplet interface, which creates an attractive force between the jumping droplet and the condensing surface. Using this knowledge, we demonstrate a novel condensation mechanism whereby an external electric field is used to oppose the droplet-surface attraction, further enhancing the coalescing droplet jumping frequency and overall surface heat transfer.

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