Three dimensional aspects of droplet coalescence during dropwise condensation on superhydrophobic surfaces

Soft Matter ◽  
2011 ◽  
Vol 7 (19) ◽  
pp. 8749 ◽  
Author(s):  
Konrad Rykaczewski ◽  
John Henry J. Scott ◽  
Sukumar Rajauria ◽  
Jeff Chinn ◽  
Amy M. Chinn ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Superhydrophobic Surfaces ◽  
Dropwise Condensation ◽  
Droplet Coalescence

scholarly journals Drops bouncing off macro-textured superhydrophobic surfaces

2017 ◽  
Vol 824 ◽  
pp. 866-885 ◽  
Author(s):  
Ali Mazloomi Moqaddam ◽  
Shyam S. Chikatamarla ◽  
Iliya V. Karlin
Keyword(s):  
Contact Time ◽  
Numerical Study ◽  
Three Dimensional ◽  
Superhydrophobic Surfaces ◽  
Nonlinear Behaviour ◽  
Textured Surfaces ◽  
Texture Density ◽  
Wide Range ◽  
Quantitative Manner ◽  
The Impact

Recent experiments with droplets impacting macro-textured superhydrophobic surfaces revealed new regimes of bouncing with a remarkable reduction of the contact time. Here we present a comprehensive numerical study that reveals the physics behind these new bouncing regimes and quantifies the roles played by various external and internal forces. For the first time, accurate three-dimensional simulations involving realistic macro-textured surfaces are performed. After demonstrating that simulations reproduce experiments in a quantitative manner, the study is focused on analysing the flow situations beyond current experiments. We show that the experimentally observed reduction of contact time extends to higher Weber numbers, and analyse the role played by the texture density. Moreover, we report a nonlinear behaviour of the contact time with the increase of the Weber number for imperfectly coated textures, and study the impact on tilted surfaces in a wide range of Weber numbers. Finally, we present novel energy analysis techniques that elaborate and quantify the interplay between the kinetic and surface energy, and the role played by the dissipation for various Weber numbers.

Droplet coalescence on water repellant surfaces

Soft Matter ◽  
2015 ◽  
Vol 11 (1) ◽  
pp. 154-160 ◽  
Author(s):  
Youngsuk Nam ◽  
Donghyun Seo ◽  
Choongyeop Lee ◽  
Seungwon Shin
Keyword(s):  
Superhydrophobic Surfaces ◽  
Water Repellent ◽  
Droplet Coalescence

We report our hydrodynamic and energy analyses of droplet coalescence on water repellent surfaces including hydrophobic, superhydrophobic and oil-infused superhydrophobic surfaces.

Wetting of rough three-dimensional superhydrophobic surfaces

2005 ◽  
Vol 12 (3) ◽  
pp. 273-281 ◽  
Author(s):  
Michael Nosonovsky ◽  
Bharat Bhushan
Keyword(s):  
Three Dimensional ◽  
Superhydrophobic Surfaces

Resistant Energy Analysis of Dropwise Condensation on Superhydrophobic Surfaces With Hierarchical Roughness

2017 ◽  
Author(s):  
Jiangtao Cheng
Keyword(s):  
Contact Line ◽  
Growth Dynamics ◽  
Adhesion Energy ◽  
Superhydrophobic Surfaces ◽  
Dropwise Condensation ◽  
Textured Surfaces ◽  
Biomimetic Surfaces ◽  
Molecular Kinetic Theory ◽  
Submicron Scale ◽  
Second Tier

Recently there have appeared multiscale lotus-leaf-like superhydrophobic surfaces that can enhance dropwise condensation in well-tailored supersaturation conditions. However, designs of most biomimetic surfaces were not driven by the understanding of underlying physical mechanisms. We report energy-based analysis of growth dynamics of condensates from surface cavities. As observed in condensation experiments, these textured surfaces with two tier roughness are superior to flat or solely nanotextured surfaces in spatial control of condensate droplets. To understand the role of condensate state transition in enhancing condensation heat transfer, we considered adhesion energy, viscous dissipation and contact line dissipation as the main portion of resistant energy that needs to be overcome by the condensates formed in surface cavities. By minimizing the energy barrier associated with the self-pulling process, we optimized first tier roughness on the hierarchically textured surfaces allowing condensates to grow preferentially in the out-of-plane direction. The nano-roughness of the second tier plays an important role in abating the adhesion energy in the cavities and contact line pinning. From the perspective of molecular kinetic theory, the dual scale engineered surface is beneficial to remarkably mitigating contact line dissipation. This study indicates that scaling down surface roughness to submicron scale can facilitate self-propelled condensate removal.

Numerical simulations of self-propelled jumping upon drop coalescence on non-wetting surfaces

2014 ◽  
Vol 752 ◽  
pp. 39-65 ◽  
Author(s):  
Fangjie Liu ◽  
Giovanni Ghigliotti ◽  
James J. Feng ◽  
Chuan-Hua Chen
Keyword(s):  
Numerical Simulations ◽  
Liquid Bridge ◽  
Flat Surface ◽  
Three Dimensional ◽  
Superhydrophobic Surfaces ◽  
Ohnesorge Number ◽  
Drop Coalescence ◽  
Out Of Plane ◽  
Potential Applications ◽  
Cutoff Radius

AbstractCoalescing drops spontaneously jump out of plane on a variety of biological and synthetic superhydrophobic surfaces, with potential applications ranging from self-cleaning materials to self-sustained condensers. To investigate the mechanism of self-propelled jumping, we report three-dimensional phase-field simulations of two identical spherical drops coalescing on a flat surface with a contact angle of 180°. The numerical simulations capture the spontaneous jumping process, which follows the capillary–inertial scaling. The out-of-plane directionality is shown to result from the counter-action of the substrate to the impingement of the liquid bridge between the coalescing drops. A viscous cutoff to the capillary–inertial velocity scaling is identified when the Ohnesorge number of the initial drops is around 0.1, but the corresponding viscous cutoff radius is too small to be tested experimentally. Compared to experiments on both superhydrophobic and Leidenfrost surfaces, our simulations accurately predict the nearly constant jumping velocity of around 0.2 when scaled by the capillary–inertial velocity. By comparing the simulated drop coalescence processes with and without the substrate, we attribute this low non-dimensional velocity to the substrate intercepting only a small fraction of the expanding liquid bridge.

Dewetting Transitions of Dropwise Condensation on Nanotexture-Enhanced Superhydrophobic Surfaces

ACS Nano ◽  
2015 ◽  
Vol 9 (12) ◽  
pp. 12311-12319 ◽  
Author(s):  
Cunjing Lv ◽  
Pengfei Hao ◽  
Xiwen Zhang ◽  
Feng He
Keyword(s):  
Superhydrophobic Surfaces ◽  
Dropwise Condensation

Scale Effect on Dropwise Condensation on Superhydrophobic Surfaces

2014 ◽  
Vol 6 (16) ◽  
pp. 14353-14359 ◽  
Author(s):  
Ching-Wen Lo ◽  
Chi-Chuan Wang ◽  
Ming-Chang Lu
Keyword(s):  
Scale Effect ◽  
Superhydrophobic Surfaces ◽  
Dropwise Condensation

Pressure Drop Measurements in Turbulent Channel Flow Over Superhydrophobic Surfaces With Riblets

2014 ◽  
Author(s):  
Joseph F. Prince ◽  
Daniel Maynes ◽  
Julie Crockett
Keyword(s):  
Pressure Drop ◽  
Test Section ◽  
Three Dimensional ◽  
Turbulent Channel Flow ◽  
Superhydrophobic Surfaces ◽  
Number Range ◽  
Patterned Wafers ◽  
Control Section ◽  
Maximum Drag Reduction ◽  
Surface Fabrication

In this paper we consider the combined drag reducing mechanisms of superhydrophobicity with riblets. Pressure drop measurements were acquired for turbulent flow in a channel with superhydrophobic walls, riblet walls, and walls with both drag reducing mechanisms. The superhydrophobic structuring was composed of alternating microribs (15 microns tall and 8 microns wide) and cavities (32 microns wide), aligned parallel to the flow. Superhydrophobic surfaces function to reduce drag by minimizing the effective liquid-solid contact area as water will not penetrate the cavities between microribs due to surface tension. The riblets were nominally 80 microns tall, 18 microns wide, spaced with a period of 160 microns and were also aligned parallel to the flow. Riblets function by damping out spanwise turbulent motions. Since turbulence is a three-dimensional phenomenon, this destruction of turbulent motions acts to reduce the average friction at the surface. Fabrication of the drag reducing surfaces was completed with photolithographic techniques on silicon wafers. The wafers were inserted into a channel consisting of a control section with smooth wafers and a test section with patterned wafers. In all cases, the test section walls were structured on top and bottom while the side walls were left smooth. The channel had a hydraulic diameter of 7.3 mm and an aspect ratio of 10:1. Tests were obtained over a Reynolds number range of 5 × 103 to 1.5 × 104. The superhydrophobic surfaces with riblets showed a maximum drag reduction of 7.0% which was a higher reduction than either the surfaces patterned with riblets or the superhydrophobic surfaces.

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