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Wetting & Wicking Effects of Superhydrophilic Nano-Structured Coatings

[+] Author and Article Information
Adam Girard

Multi-Scale Heat Transfer Lab, Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
adam.girard@utdallas.edu

Miguel Amaya

Department of Mechanical & Aerospace Engineering, The University of Texas at Arlington, Arlington, TX 76019, USA
mamaya@uta.edu

Hyoseong Wi

Multi-Scale Heat Transfer Lab, Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
hyoseong.wi@hyundai.com

Seung M. You

Multi-Scale Heat Transfer Lab, Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
you@utdallas.edu

Corresponding author.

J. Heat Transfer 137(8), 080908 (Aug 01, 2015) Paper No: HT-15-1256; doi: 10.1115/1.4030472 History: Received March 31, 2015; Revised April 02, 2015; Online June 01, 2015

Abstract

Superhydrophilic Nano-Structured Coatings (SHNC) were discovered during pool boiling experiments using nanofluids with alumina nanoparticles. During nucleate boiling, the nanoparticles are deposited on the heater surface, forming a uniform oxide coating. These coatings have been demonstrated to greatly decrease the liquid contact angle observed on the surfaces, both by increased surface roughness and increased surface energy. An illustration of this roughness, within 1 μm thickness, can be seen in the 3-D optical microscope mapping of a SHNC surface, top right. These highly wetting structures can greatly enhance macro-level mass transfer effects, such as capillary action. The series of images on the left depict the wickability enhancement achieved by SHNC coating inside a 0.92 mm internal diameter aluminum tube. In the tube coated with SHNC, a 21 μl water droplet disappeared in 183 milliseconds, resulting in an average wicking speed along the pipe of 17 cm/sec. The bare aluminum tube does not wick at all, even as it is pushed into the droplet. The bottom right sequence shows the wettability enhancement responsible for this behavior; an 8 μl water droplet is dropped onto both a SHNC-coated and a bare aluminum surface from a height of 1 cm. The droplet on the SHNC-coated surface spreads instantaneously due to the high wettability of the SHNC, while the droplet on the bare aluminum remains aggregated as a hemisphere.

Copyright © 2015 by ASME
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