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Oct 2009

Volume 21, Issue 10, Articles (10xxxx)

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Phys. Fluids 21, 104102 (2009); http://dx.doi.org/10.1063/1.3243976 (13 pages)

Denis Martinand, Eric Serre, and Richard M. Lueptow
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back to top Micro- and Nanofluid Mechanics

Entrainment of a film on a surface from the meniscus of a liquid wedge during coating

S. N. Reznik, W. Salalha, Y. Sorek, D. Avramov, and E. Zussman

Phys. Fluids 21, 102001 (2009); http://dx.doi.org/10.1063/1.3240396 (14 pages) | Cited 1 time

Online Publication Date: 1 October 2009

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The shape evolution of an entrained film from the meniscus of a liquid wedge is studied, both experimentally and theoretically. The liquid wedge is formed by a droplet of liquid injected between a substrate and a tilted plate. When the substrate moves relative to the tilted plate with a constant velocity, a film of a constant slope is entrained on it, while another film remains on the tilted plate. The numerical and analytical investigation of the process provides the dependence of the length and slope of the entrained film after the end of drawing process, as well as the maximum thickness of the film on the tilted plate, on the capillary number. The length of the entrained film was found to be minimal for infinitely large capillary numbers when the surface tension effects are negligibly small. Experimental data confirm the predicted characteristic geometry of the film for capillary numbers up to 0.75.
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47.55.Hd Stratified flows
68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
47.55.dr Interactions with surfaces
47.55.nb Capillary and thermocapillary flows
68.15.+e Liquid thin films

Transport properties of Brownian particles confined to a narrow channel by a periodic potential

Xinli Wang and German Drazer

Phys. Fluids 21, 102002 (2009); http://dx.doi.org/10.1063/1.3226100 (7 pages) | Cited 1 time

Online Publication Date: 2 October 2009

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We investigate the transport of Brownian particles in a two-dimensional potential moving under the action of an external force or convected by a flow field. The potential is periodic in one direction and confines the particles to a narrow channel of varying cross section in the other direction. We apply the standard long-wave asymptotic analysis in the narrow dimension and show that the leading order term is equivalent to that obtained previously from a direct extension of the Fick–Jacobs approximation. We also show that the confining potential has similar effects on the transport of Brownian particles to those induced by a solid channel. Finally, we compare the analytical results with Brownian dynamics simulations in the case of a sinusoidal variation of the width of a parabolic potential in the cross section. We obtain excellent agreement for the marginal probability distribution, the average velocity of the Brownian particles, and the asymptotic dispersion coefficient over a wide range of Péclet numbers.
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05.40.Jc Brownian motion
47.60.Dx Flows in ducts and channels
FREE

Nucleation threshold and deactivation mechanisms of nanoscopic cavitation nuclei

Bram M. Borkent, Stephan Gekle, Andrea Prosperetti, and Detlef Lohse

Phys. Fluids 21, 102003 (2009); http://dx.doi.org/10.1063/1.3249602 (9 pages) | Cited 14 times

Online Publication Date: 19 October 2009

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The acoustic nucleation threshold for bubbles trapped in cavities has theoretically been predicted within the crevice theory by Atchley and Prosperetti [“The crevice model of bubble nucleation,” J. Acoust. Soc. Am. 86, 1065 (1989) ]. Here, we determine this threshold experimentally, by applying a single pressure pulse to bubbles trapped in cylindrical nanoscopic pits (“artificial crevices”) with radii down to 50 nm. By decreasing the minimum pressure stepwise, we observe the threshold for which the bubbles start to nucleate. The experimental results are quantitatively in good agreement with the theoretical predictions of Atchley and Prosperetti. In addition, we provide the mechanism which explains the deactivation of cavitation nuclei: gas diffusion together with an aspherical bubble collapse. Finally, we present superhydrophobic nuclei which cannot be deactivated, unless with a high-speed liquid jet directed into the pit.
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47.55.dp Cavitation and boiling
68.08.Bc Wetting
47.55.D- Drops and bubbles

Measurements of tangential momentum accommodation coefficient for various gases in plane microchannel

I. A. Graur, P. Perrier, W. Ghozlani, and J. G. Méolans

Phys. Fluids 21, 102004 (2009); http://dx.doi.org/10.1063/1.3253696 (9 pages) | Cited 13 times

Online Publication Date: 30 October 2009

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Mass flow rate measurements in a single silicon microchannel were carried out for various gases in isothermal steady flows. The results obtained from hydrodynamic to near free molecular regime by using a powerful experimental platform allowed us to deduce interesting information, notably about the reflection/accommodation process at the wall. In the 0–0.3 Knudsen range, a continuum analytic approach was derived from the NS equations, associated with first or second order slip boundary conditions. Identifying the experimental mass flow rate curves to the theoretical ones the tangential momentum accommodation coefficient (TMAC) of various gases was extracted. Over the full Knudsen range [0–30] the experimental results were compared with theoretical values calculated from the kinetic approaches: using variable accommodation coefficient values as fitting parameter, the theoretical curves were fitted to the experimental ones. Whatever the Knudsen range and whatever the theoretical approach, the TMAC values are found decreasing when the molecular weights of the gas increase (as long as the different gases are compared using the same approach). Moreover, the values of the various accommodation coefficients are rather close to one another but sufficiently smaller than unity indicating that the full accommodation modeling is not satisfactory to describe the gas/wall interaction.
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47.60.Dx Flows in ducts and channels
47.61.-k Micro- and nano- scale flow phenomena
47.45.Gx Slip flows and accommodation
47.10.ad Navier-Stokes equations
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