0
Research Papers: Evaporation, Boiling, and Condensation

An Exploration of Transport Within Microdroplet and Nanodroplet Clusters During Dropwise Condensation of Water on Nanostructured Surfaces

[+] Author and Article Information
Hector Mendoza, Sara Beaini

Mechanical Engineering Department,
University of California,
Berkeley, CA 94720-1740

Van P. Carey

Mechanical Engineering Department,
University of California,
Berkeley, CA 94720-1740
e-mail: vcarey@me.berkeley.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received February 24, 2012; final manuscript received November 30, 2013; published online October 21, 2014. Assoc. Editor: Leslie Phinney.

J. Heat Transfer 136(12), 121501 (Oct 21, 2014) (9 pages) Paper No: HT-12-1069; doi: 10.1115/1.4026167 History: Received February 24, 2012; Revised November 30, 2013

Experimental studies of dropwise condensation have generally indicated that higher heat transfer coefficients correspond to smaller mean sizes for droplets growing through condensation on the surface. Recent investigations of dropwise condensation on nanostructured surfaces suggest that optimizing the design of such surfaces can push mean droplet sizes down to smaller values and significantly enhance heat transfer. This paper summarizes a theoretical exploration of the limits of heat transfer enhancement that can be achieved by pushing mean droplet size to progressively smaller sizes. A model analysis is developed that predicts transport near clusters of water droplets undergoing dropwise condensation. The model accounts for interfacial tension effects on thermodynamic equilibrium and noncontinuum transport effects, which become increasingly important as droplet size becomes progressively smaller. In this investigation, the variation of condensing heat transfer coefficient for droplet clusters of different sizes was explored for droplet diameters ranging from hundreds of microns to tens of nanometers. The model predictions indicate that the larger droplet transport trend of increasing heat transfer coefficient with decreasing mean droplet size breaks down as droplet size becomes smaller. The model further predicts that as drop size becomes smaller, a peak heat transfer coefficient is reached, beyond which the coefficient drops as the size continues to diminish. This maximum heat transfer coefficient results from the increasing importance of surface tension effects and noncontinuum effects as droplet size becomes smaller. The impact of these predictions on the interpretation of dropwise condensation heat transfer data, and the implications for design of nanostructured surfaces to enhance dropwise condensation are discussed in detail.

FIGURES IN THIS ARTICLE
<>
Copyright © 2014 by ASME
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Fig. 1

Mechanisms affecting dropwise condensation transport

Grahic Jump Location
Fig. 2

Model unit-cell system

Grahic Jump Location
Fig. 3

Model of computational domain used in Monte Carlo method determination of Fus, Fid, and Fii

Grahic Jump Location
Fig. 4

Predicted variation of the fraction of particles passing through the upper aperture surface of the unit cell striking a droplet (Fus) with s/d and θ in the ballistic limit

Grahic Jump Location
Fig. 5

Predicted variation of the fraction of particles emitted from a droplet interface that strike a different droplet (Fid) with s/d and θ in the ballistic limit

Grahic Jump Location
Fig. 6

Predicted variation of the fraction of particles emitted from a droplet interface that return to the same droplet (Fii) with s/d and θ in the ballistic limit

Grahic Jump Location
Fig. 7

Variation of heat transfer coefficient with droplet diameter for σ = 1, T − Tw = Tsat(P) − Tw = 3.0 K, P = 101 kPa, and s/d = 0.4

Grahic Jump Location
Fig. 8

Variation of heat transfer coefficient with droplet diameter for σ = 0.9, T − Tw = Tsat(P) − Tw = 3.0 K, P = 101 kPa, and s/d = 0.4

Grahic Jump Location
Fig. 9

Variation of heat transfer coefficient with droplet diameter for σ = 1, T − Tw = Tsat(P) − Tw = 3.0 K, P = 5.05 kPa, and s/d = 0.4

Grahic Jump Location
Fig. 10

Variation of heat transfer coefficient with droplet diameter for σ = 1, T − Tw = Tsat(P) − Tw = 3.0 K, P = 101 kPa, and s/d = 1.0

Grahic Jump Location
Fig. 11

Variation of heat transfer coefficient with droplet diameter for σ = 1, T − Tw = Tsat(P) − Tw = 7.0 K, P = 101 kPa, and s/d = 0.4

Grahic Jump Location
Fig. 12

Coordinate system

Grahic Jump Location
Fig. 13

Specular reflection at lateral planes of unit cell

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In