Research Papers: Evaporation, Boiling, and Condensation

Dropwise Condensation on/in High Roughness Structures

[+] Author and Article Information
Steve Q. Cai

Teledyne Scientific Company,
1049 Camino Dos Rios,
Thousand Oaks, CA 91360
e-mail: qingjun.cai@teledyne.com

Avijit Bhunia

Teledyne Scientific Company,
1049 Camino Dos Rios,
Thousand Oaks, CA 91360

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received December 22, 2015; final manuscript received November 17, 2016; published online January 18, 2017. Assoc. Editor: Jim A. Liburdy.

J. Heat Transfer 139(4), 041501 (Jan 18, 2017) (6 pages) Paper No: HT-15-1808; doi: 10.1115/1.4035354 History: Received December 22, 2015; Revised November 17, 2016

Water droplets on bio-mimicked hierarchical roughness exhibit superhydrophobic properties, such as large contact angles, minor dynamic hysteresis, and high mobility. Vapor condensation on such superhydrophobic surface enables rapid condensate removal and surface cleaning, thereby significantly enhancing the heat transfer coefficient. In this paper, research attention is given to dropwise condensation on/in specially designed one-tier and hierarchical roughness structures. Utilizing a normal optical tomographic system composed of a Sensi-Cam and a Nikon microscope, close-up visualization is conducted to characterize small condensate droplets, in size of a few micrometers, between structural units of roughness. Experimental snapshots show that, within the one-tier roughness, condensate droplets tend to stick to surrounding structures. Low mobility of these droplets extends their residence time, and therefore increases their average diameter. In comparison, surface energy of the hierarchical structure is significantly reduced. As a result, small condensate droplets behave nonsticky to their surroundings, which enable rapid drain of the droplets and accomplish self-cleaning of the structure. Because of high mobility, the droplet average diameter in the two-tier structure is smaller than those in the one-tire roughness. Condensation sites reach the maximum in the middle of the structure where dew point of moisture is reached. Less condensation droplets on both the top and bottom of the roughness are blamed to the unsaturated moisture and the reduced humidity, respectively.

Copyright © 2017 by ASME
Your Session has timed out. Please sign back in to continue.


Wang, S. , and Jiang, L. , 2007, “ Definition of Superhydrophobic States,” Adv. Mater., 19(21), pp. 3423–3424. [CrossRef]
Wenzel, R. N. , 1936, “ Resistance of Solid Surfaces to Wetting by Water,” Int. Eng. Chem., 28(8), pp. 988–994.
Cassie, A. B. , and Baxter, B. , 1944, “ Wettability of Porous Surfaces,” Trans. Faraday Soc., 40, pp. 546–551. [CrossRef]
Lafuma, A. , and Quere, D. , 2003, “ Superhydrophobic States,” Lett. Nat., 2(7), pp. 457–460. [CrossRef]
Albert, G. , 2000, Variational Models for Phase Transitions, An Approach Via Γ-Convergence. Differential Equations and Calculus of Variations (Topics on Geometrical Evolution Problems and Degree Theory), Springer, Berlin, pp. 95–114.
Quere, D. , 2005, “ Non-Sticking Drops,” Rep. Prog. Phys., 68(11), pp. 2495–2532. [CrossRef]
Cheng, Y. T. , Rodak, D. E. , Angelopoulos, A. , and Gacek, T. , 2005, “ Microscopic Observations of Condensation of Water on Lotus Leaves,” Appl. Phys. Lett., 87(19), p. 194112. [CrossRef]
Chen, C. H. , Cai, Q. , Tsai, C. , Chen, C. L. , Xiong, G. Y. , Yu, Y. , and Ren, Z. F. , 2007, “ Dropwise Condensation on Superhydrophobic Surfaces With Two-Tier Roughness,” Appl. Phys. Lett., 90(17), p. 173108. [CrossRef]
Dorrer, C. , and Ruhe, J. , 2007, “ Condensation and Wetting Transitions on Microstructured Ultrahydrophobic Surfaces,” Langmuir, 23(7), pp. 3820–3824. [CrossRef] [PubMed]
Narhe, R. D. , and Beysens, D. A. , 2006, “ Water Condensation on a Super-Hydrophobic Spike Surface,” Europhys. Lett., 75(1), pp. 98–104. [CrossRef]
Narhe, R. D. , and Beysens, D. A. , 2007, “ Growth Dynamics of Water Drops on a Square-Pattern Rough Hydrophobic Surface,” Langmuir, 23(12), pp. 6486–6489. [CrossRef] [PubMed]
Liu, T. , Sun, W. , Sun, X. , and Ai, H. , 2010, “ Thermodynamic Analysis of the Effect of the Hierarchical Architecture of a Superhydrophobic Surface on a Condensed Drop State,” Langmuir, 26(18), pp. 14835–14841. [CrossRef] [PubMed]
Dietz, C. , Rykaczewski, K. , Fedorov, A. G. , and Joshi, Y. , 2010, “ Visualization of Droplet Departure on a Superhydrophobic Surface and Implications to Heat Transfer Enhancement During Dropwise Condensation,” Appl. Phys. Lett., 97(3), p. 033104. [CrossRef]
Miljkovic, N. , Enright, R. , and Wang, E. N. , 2012, “ Effect of Droplet Morphology on Growth Dynamics and Heat Transfer During Condensation on Superhydrophobic Nanostructured Surfaces,” ACS Nano, 6(2), pp. 1776–1785. [CrossRef] [PubMed]
Darmanina, T. , and Guittard, F. , 2014, “ Recent Advances in the Potential Applications of Bioinspired Superhydrophobic Materials,” J. Mater. Chem. A, 2(39), pp. 16319–16359. [CrossRef]


Grahic Jump Location
Fig. 2

High-aspect ratio roughness and hierarchical structure decrease the critical contact angle to stabilize the Cassie state

Grahic Jump Location
Fig. 1

Hydrophobicity states of droplets on surface roughness

Grahic Jump Location
Fig. 3

Roughness structures for dropwise condensation studies: (a) one-tier conical roughness structure, (b) zoom-in of tapered silicon pillars, (c) hierarchical roughness structure, and (d) fabric CNTs synthesized on tip of the silicon pillars

Grahic Jump Location
Fig. 4

Visualization of dropwise condensation on/in the roughness structures: (a) visualization system, (b) a roughness sample placed between the copper cold plate and the microscope, and (c) a schematic of the normal optical tomography

Grahic Jump Location
Fig. 5

The Cassie state droplets over the roughness structures: (a) liquid bridges and spherical droplets co-exist in/on the one-tier roughness and (b) spherical droplets on the two-tier structure

Grahic Jump Location
Fig. 6

Dropwise condensation views in the one-tier roughness structure: (a) at the tip of the structure, (b) in 1/3 depth, (c) in 2/3 depth, and (d) on the bottom of structure

Grahic Jump Location
Fig. 9

Average droplet diameter versus the structural depth of both the one-tier and hierarchical roughness

Grahic Jump Location
Fig. 10

Schematic diagram of dropwise condensation and precipitation on the one-tier and hierarchical roughness with conical tips: (a) in a one-tier structure, a distorted droplet between the silicon pillars creating capillary force difference for draining and (b) condensate droplets can be drained from the bottom of the hierarchical roughness

Grahic Jump Location
Fig. 7

Droplet condensation in the hierarchical roughness structure: (a) at the tips of silicon pillars, (b) at 1/3 depth, (c) at 2/3 depth, and (d) at the bottom

Grahic Jump Location
Fig. 8

Droplet density versus the structural depth of both the one-tier and hierarchical roughness



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