A multiscale approach to interpret and predict the apparent slip velocity at liquid-liquid interfaces

Total internal reflection fluorescent microscopy (TIRFM) is used to measure particle motion in the near wall region of a microfluidic system. TIRFM images have minimum background noise and contain only particles that are very close to channel surface, where slip velocities may be present. Submicron sized fluorescent particles suspended in water are used as seed particles and images are analyzed with a PTV algorithm to extract information about apparent slip velocity. At relatively low shear rates (less than 2500 sec−1), an apparent slip velocity, proportional to the shear rate was observed. However, numerical simulations show that this observation is a direct consequence of the small, but finite thickness of the illuminated region, and most likely not due to physical slip at the surface. The statistical difference in apparent slip velocities measured over hydrophilic and hydrophobic surfaces is found to be minimal. Issues associated with the experimental technique and the interpretation of the experimental results are also discussed.

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Flow at the interface of a model fibrous porous medium

Journal of Fluid Mechanics ◽

10.1017/s0022112000002160 ◽

2001 ◽

Vol 426 ◽

pp. 47-72 ◽

Cited By ~ 96

Author(s):

DAVID F. JAMES ◽

ANTHONY M. J. DAVIS

Keyword(s):

Porous Medium ◽

Slip Velocity ◽

Volume Fraction ◽

Solid Volume Fraction ◽

Circular Cylinders ◽

Interfacial Region ◽

Filling Fraction ◽

Apparent Slip ◽

Square Array ◽

Pressure Driven Flow

Planar flow in the interfacial region of an open porous medium is investigated by finding solutions for Stokes flow in a channel partially filled with an array of circular cylinders beside one wall. The cylinders are in a square array oriented across the flow and are widely spaced, so that the solid volume fraction ϕ is 0.1 or less. For this spacing, singularity methods are appropriate and so they are used to find solutions for both planar Couette flow and Poiseuille flow in the open portion of the channel. The solutions, accurate to O(ϕ), are used to calculate the apparent slip velocity at the interface, Us, and results obtained for Us are presented in terms of a dimensionless slip velocity. For shear-driven flow, this dimensionless quantity is found to depend only weakly on ϕ and to be independent of the height of the array relative to the height of the channel and independent of the cylinder size relative to the height of the channel. For pressure-driven flow, Us is found to be less than that under comparable shear-flow conditions, and dependent on cylinder size and filling fraction in this case. Calculations also show that the external flow penetrates the porous medium very little, even for sparse arrays, and that Us is about one quarter of the velocity predicted by the Brinkman model.

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Apparent slip velocity of paper coatings in viscometric flows

Nordic Pulp & Paper Research Journal ◽

10.3183/npprj-2000-15-05-p502-508 ◽

2000 ◽

Vol 15 (5) ◽

pp. 502-508 ◽

Cited By ~ 2

Author(s):

Annaleena Kokko ◽

Tom Grankvist ◽

Nick Triantafillopoulos

Keyword(s):

Slip Velocity ◽

Paper Coatings ◽

Apparent Slip

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Slip of Liquid Flow at a Hydrophobic Surface : A Simulation Model for Apparent Slip Velocity

The proceedings of the JSME annual meeting ◽

10.1299/jsmemecjo.2003.2.0_231 ◽

2003 ◽

Vol 2003.2 (0) ◽

pp. 231-232

Author(s):

Takao FUJITA ◽

Keizo WATANABE

Keyword(s):

Simulation Model ◽

Liquid Flow ◽

Slip Velocity ◽

Hydrophobic Surface ◽

Apparent Slip

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Effects of the finite particle size in turbulent wall-bounded flows of dense suspensions

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.117 ◽

2018 ◽

Vol 843 ◽

pp. 450-478 ◽

Cited By ~ 20

Author(s):

Pedro Costa ◽

Francesco Picano ◽

Luca Brandt ◽

Wim-Paul Breugem

Keyword(s):

Particle Size ◽

Newtonian Fluid ◽

Size Effects ◽

Slip Velocity ◽

Finite Size ◽

Particle Dynamics ◽

Wall Layer ◽

Shear Stresses ◽

Finite Size Effects ◽

Apparent Slip

We use interface-resolved numerical simulations to study finite-size effects in turbulent channel flow of neutrally buoyant spheres. Two cases with particle sizes differing by a factor of two, at the same solid volume fraction of 20 % and bulk Reynolds number are considered. These are complemented with two reference single-phase flows: the unladen case, and the flow of a Newtonian fluid with the effective suspension viscosity of the same mixture in the laminar regime. As recently highlighted in Costa et al. (Phys. Rev. Lett., vol. 117, 2016, 134501), a particle–wall layer is responsible for deviations of the mesoscale-averaged statistics from what is observed in the continuum limit where the suspension is modelled as a Newtonian fluid with (higher) effective viscosity. Here we investigate in detail the fluid and particle dynamics inside this layer and in the bulk. In the particle–wall layer, the near-wall inhomogeneity has an influence on the suspension microstructure over a distance proportional to the particle size. In this layer, particles have a significant (apparent) slip velocity that is reflected in the distribution of wall shear stresses. This is characterized by extreme events (both much higher and much lower than the mean). Based on these observations we provide a scaling for the particle-to-fluid apparent slip velocity as a function of the flow parameters. We also extend the scaling laws in Costa et al. (Phys. Rev. Lett., vol. 117, 2016, 134501) to second-order Eulerian statistics in the homogeneous suspension region away from the wall. The results show that finite-size effects in the bulk of the channel become important for larger particles, while negligible for lower-order statistics and smaller particles. Finally, we study the particle dynamics along the wall-normal direction. Our results suggest that single-point dispersion is dominated by particle–turbulence (and not particle–particle) interactions, while differences in two-point dispersion and collisional dynamics are consistent with a picture of shear-driven interactions.

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Study on Wall Slip in Pipeline Flow of Dense Paste

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.511-512.50 ◽

2014 ◽

Vol 511-512 ◽

pp. 50-54

Author(s):

Fu Yan Lv ◽

Zheng Meng Xia ◽

Jie Gao ◽

Xue Di Hao ◽

Miao Wu

Keyword(s):

Slip Velocity ◽

Particle Concentration ◽

Wall Slip ◽

Test System ◽

Pipe Diameter ◽

Coal Slurry ◽

Slip Mechanism ◽

Apparent Slip ◽

Slip Layer

The apparent wall slip flows of incompressible and viscoplastic fluids in plane pipeline were analyzed assuming that the apparent slip layer consists solely wall slip layershear layerslug flow part and they are independent of the flow rate. Taking coal slurry for example,the experiment is conducted on pressure pipe rheological and resistance characteristic test system. It studies how two key factors (the particle concentration and the pipe diameter) influence the dense paste wall slip velocity. The assumed apparent slip mechanism provides methodologies for the determination of the slip velocity values that are consistent with the traditional Mooney method and furthermore allows the determination of the true shear rate of the dense paste at the wall and the yield stress. The analysis of the slip data of various dense pastes of rigid particles reveals that the apparent slip layer thickness is related to the particle concentration and the pipe diameter.

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