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The Effect of Surface Wettability on Viscous Film Deposition

[+] Author Affiliations
Alexandru Herescu, Jeffrey S. Allen

Michigan Technological University, Houghton, MI

Paper No. ICNMM2009-82263, pp. 661-664; 4 pages
doi:10.1115/ICNMM2009-82263
From:
  • ASME 2009 7th International Conference on Nanochannels, Microchannels, and Minichannels
  • ASME 2009 7th International Conference on Nanochannels, Microchannels and Minichannels
  • Pohang, South Korea, June 22–24, 2009
  • Conference Sponsors: Nanotechnology Institute
  • ISBN: 978-0-7918-4349-9 | eISBN: 978-0-7918-3850-1
  • Copyright © 2009 by ASME

abstract

The viscous deposition of a liquid film on the inside of a capillary has been experimentally investigated with a focus on the relationship between the film thickness and surface wettability. With distilled water as a working fluid tests were run in a 622 microns diameter glass tube with contact angles of 30° and 105°, respectively. In the first set of experiments the tube was uncoated while in the second set a fluoropolymer coating was applied to increase the contact angle. A film thickness dependence with the contact angle θ (surface wettability) as well as the Capillary number in the form hRCa2/3 /cosθ is inferred from scaling arguments. For partial wetting it may explain the existence of a thicker film for nonzero contact angle. It was further found that the non-wetting case of 105° contact angle deviates significantly from the existing theories, the film thickness presenting a weak dependence with the Capillary number. This deviation as well as the apparent non-uniqueness of the solution is thought to be caused by the film instability (rupture) observed during the tests. The thickness of the deposited film as a function of the Capillary number was estimated from the liquid mass exiting the capillary and the gas-liquid interface (meniscus) velocity, and compared to Bretherton’s data and a correlation proposed by Quere. The film thickness measurements as well as the meniscus velocity were determined with the aid of a Photron high speed camera with 10000 frames per second sampling capability coupled with a Nikon TE-2000 inverted microscope and a Precisa electronic balance.

Copyright © 2009 by ASME

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