Depicted are sequences of water drop impacts on copper, taken at 16,000 fps. The copper is treated with a heated alkali solution, resulting in a highly wetting, nanoscale structured, cupric oxide layer with a static contact angle approaching 0° with water. In the top series an 11.5 µl water droplet impacts this surface from 60 mm. The interfacial forces are large compared with the inertia; the low advancing contact angle of the expanding front continues to pull the droplet outward and absorbs the droplet without any rebound. The droplet spreads to cover the entire 0.5x0.5 in2 surface in less than 500 ms. After the surface energy of the oxide layer is reduced with silane, this surface becomes highly non-wetting with a static contact angle of ~160° and a hysteresis <5°. The lower sequence shows the 11.5 µl water droplet dropped from the same height. The large advancing contact angle creates an inverted wedge at the triple line, and the advancing front quickly reaches a maximum diameter at 3 ms and begins to recede inward while the top of the droplet is still moving downward, creating a donut shape. The receding front collides at the center forcing a jet of liquid up and out. This jet pulls the remainder of the liquid upward at a decreasing velocity, relative to the head. This is apparent as the jet splits into secondary droplets at 16ms (which moves out of frame at 18 ms) and again at 22 ms, referred to as S-1 and S-2, respectively. As the S-2 splits off, surface tension force cause it to slow at 25 ms, while the parent droplet moves up to collide with, and impart momentum to S-2. They remain detached; S-2 moves out of view, the parent falls. This bouncing behavior continues until the energy is dissipated and the droplets come to rest. This can be seen as the parent drop rebounds again at 100ms, S-2 at 130 ms and S-1 in the final frame, forming a tertiary droplet. These surfaces are being studied for their effects on two phase heat transfer.
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Drop Impact Variation at the Extremes of Wettability
Adam Girard,
Adam Girard
Multi-Scale Heat Transfer Lab, Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
alg130130@utdallas.edu
alg130130@utdallas.edu
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John Wolfgong,
John Wolfgong
Space and Airborne System, Raytheon Company, 2501 West University Drive, McKinney, TX 75071, USA
wolfgong@raytheon.com
wolfgong@raytheon.com
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Jinsub Kim,
Jinsub Kim
Dept. of Extreme Thermal Systems, Korea Institute of Machinery and Materials, Daejeon, Korea
jxk150430@utdallas.edu
jxk150430@utdallas.edu
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Seung M. You
Seung M. You
Multi-Scale Heat Transfer Lab, Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
you@utdallas.edu
you@utdallas.edu
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Adam Girard
Multi-Scale Heat Transfer Lab, Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
alg130130@utdallas.edu
alg130130@utdallas.edu
John Wolfgong
Space and Airborne System, Raytheon Company, 2501 West University Drive, McKinney, TX 75071, USA
wolfgong@raytheon.com
wolfgong@raytheon.com
Jinsub Kim
Dept. of Extreme Thermal Systems, Korea Institute of Machinery and Materials, Daejeon, Korea
jxk150430@utdallas.edu
jxk150430@utdallas.edu
Seung M. You
Multi-Scale Heat Transfer Lab, Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080, USA
you@utdallas.edu
you@utdallas.edu
1Corresponding author.
J. Heat Transfer. Aug 2016, 138(8): 080909 (1 pages)
Published Online: July 8, 2016
Article history
Received:
April 13, 2016
Revised:
June 3, 2016
Citation
Girard, A., Wolfgong, J., Kim, J., and You, S. M. (July 8, 2016). "Drop Impact Variation at the Extremes of Wettability." ASME. J. Heat Transfer. August 2016; 138(8): 080909. https://doi.org/10.1115/1.4033816
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