Research Papers: Evaporation, Boiling, and Condensation

Dropwise Condensation Modeling Suitable for Superhydrophobic Surfaces

[+] Author and Article Information
Sunwoo Kim

Department of Mechanical Engineering, P.O. Box 755905, University of Alaska, Fairbanks, AK 99775swkim@alaska.edu

Kwang J. Kim

Department of Mechanical Engineering, MS312, Low Carbon Green Technology Laboratory (LCGTL), University of Nevada, Reno, NV 89557kwangkim@unr.edu

J. Heat Transfer 133(8), 081502 (May 03, 2011) (8 pages) doi:10.1115/1.4003742 History: Received December 25, 2009; Revised February 25, 2011; Published May 03, 2011; Online May 03, 2011

A mathematical model is developed to represent and predict the dropwise condensation phenomenon on nonwetting surfaces having hydrophobic or superhydrophobic (contact angle greater than 150 deg) features. The model is established by synthesizing the heat transfer through a single droplet with the drop size distribution. The single droplet heat transfer is analyzed as a combination of the vapor-liquid interfacial resistance, the resistance due to the conduction through the drop itself, the resistance from the coating layer, and the resistance due to the curvature of the drop. A population balance model is adapted to develop a drop distribution function for the small drops that grow by direct condensation. Drop size distribution for large drops that grow mainly by coalescence is obtained from a well-known empirical equation. The evidence obtained suggests that both the single droplet heat transfer and drop distribution are significantly affected by the contact angle. More specifically, the model results indicate that a high drop-contact angle leads to enhancing condensation heat transfer. Intense hydrophobicity, which produces high contact angles, causes a reduction in the size of drops on the verge of falling due to gravity, thus allowing space for more small drops. The simulation results are compared with experimental data, which were previously reported.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

A droplet on the condensing surface coated with hydrophobic material

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Figure 2

Heat transfer by conduction between two neighboring isothermal surfaces

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Figure 3

Single drop heat transfer rate and heat flux with respect to the contact angle

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Figure 4

Drop size distributions for contact angles of 90 deg, 120 deg, and 150 deg

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Figure 5

Overall heat transfer rate per unit area versus vapor to solid surface temperature difference for contact angles of 90 deg, 120 deg, and 150 deg in comparison with filmwise condensation

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Figure 6

Model prediction and experimental results for overall heat transfer rate per unit area at a condenser pressure of 33.86 kPa

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Figure 7

Overall heat flux versus vapor subcooling for different thicknesses of coating layer

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Figure 8

Overall heat flux versus subcooling for different nucleation densities




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