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Frosting Characteristics on Hydrophilic and Superhydrophobic Copper Surfaces

[+] Author and Article Information
Chan Ho Jeong

School of Mechanical Engineering, Chung-Ang University, Seoul 156-756, Korea
chjwjeong@nate.com

Jae Bin Lee

School of Mechanical Engineering, Chung-Ang University, Seoul 156-756, Korea
jaebin1984@gmail.com

Seong Hyuk Lee

School of Mechanical Engineering, Chung-Ang University, Seoul 156-756, Korea
shlee89@cau.ac.kr

Jungho Lee

Korea Institute of Machinery & Materials, Daejeon 305-343, Korea
jungho@kimm.re.kr

Seung Mun You

Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
you@utdallas.edu

Chang Kyoung Choi

Mechanical Engineering – Engineering Mechanics, Michigan Technological University, Houghton, MI 49931
cchoi@mtu.edu

1Corresponding author.

J. Heat Transfer 138(2), 020913 (Jan 18, 2016) Paper No: HT-15-1728; doi: 10.1115/1.4032257 History: Received November 13, 2015; Revised December 02, 2015

Abstract

The main objective of this study is to examine the frosting characteristics affected by the surface wettability. Two different copper surfaces – bare and nano structured - were prepared for the experiments. Their static contact angles are 74° (bare: without surface treatment) and 154° (nano-structured), respectively. The temperature of the copper substrate was measured by using resistance temperature detector (RTD) sensors embedded inside small holes drilled at 1 mm underneath the surface. During the phase change, the temperature of the copper substrates remained -7.8±0.6°C and the ambient temperature was set as 24±0.5°C with the relative humidity of 45%. Images were captured by using the CMOS camera with the 5 second time interval. Film condensation occurred because of higher wettability of the bare copper surface. Film condensates were frozen at the early stage and frost crystal grew in the vertical direction. On the other hand, dropwise condensates formed on the nano-structured copper surface remained as the supercooled liquid phase for 44 minutes owing to its low wettability. After 4 minutes, frosting on the bare copper substrate was triggered and propagated until it covered the whole surface. The frosting was significantly delayed on the superhydrophobic copper surface due to the lower surface free energy. The different porous media composed of frost which directly influence the heat transfer characteristics was formed on each surfaces. Therefore, additional investigation for heat transfer phenomenon on superhydrophobic surface should be conducted.

Copyright © 2016 by ASME
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