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research-article

Dropwise Condensation on Superhydrophobic Microporous Wick Structures

[+] Author and Article Information
Sean Hoenig

Advanced Cooling Technologies, Inc., 1046 New Holland Avenue, Lancaster, PA 17601
sean.hoenig@1-act.com

Richard Bonner

Advanced Cooling Technologies, Inc., 1046 New Holland Avenue, Lancaster, PA 17601
richard.bonner@1-act.com

1Corresponding author.

ASME doi:10.1115/1.4038854 History: Received April 28, 2017; Revised December 06, 2017

Abstract

Previous research in dropwise condensation on rough micro-textured superhydrophobic surfaces has demonstrated evidence of high heat transfer enhancement compared to smooth hydrophobic surfaces. In this study, we experimentally investigate the use of microporous sintered copper powder on copper substrates coated with a thiol-based self-assembled monolayer to attain enhanced dropwise condensation for steam in a custom condensation chamber. Although micro-textured superhydrophobic surfaces have shown advantageous droplet growth dynamics, precise heat transfer measurements are underdeveloped at high heat flux. Sintered copper powder diameters from 4µm to 119µm were used to investigate particle size effects on heat transfer. As powder diameter decreased, competing physical factors led to improved thermal performance. At consistent operating conditions, we experimentally demonstrated a 23% improvement in the local condensation heat transfer coefficient for a superhydrophobic 4µm diameter microporous copper powder surface compared to a smooth hydrophobic copper surface. For the smallest powders observed, this improvement is primarily attributed to the reduction in contact angle hysteresis as evidenced by the decrease in departing droplet size. Interestingly, the contact angle hysteresis of sessile water droplets measured in air is in contradiction with the departing droplet size observations made during condensation of saturated steam. It is evident that the specific design of textured superhydrophobic surfaces has profound implications for enhanced condensation in high heat flux applications.

Copyright (c) 2017 by ASME
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