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Research Papers: Fundamental Issues and Canonical Flows

Effects of Channel Scale on Slip Length of Flow in Micro/Nanochannels

[+] Author and Article Information
Xiaofan Yang

Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506xiaofan@ksu.edu

Zhongquan C. Zheng1

Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506zzheng@ksu.edu

1

Corresponding author.

J. Fluids Eng 132(6), 061201 (May 19, 2010) (6 pages) doi:10.1115/1.4001619 History: Received August 14, 2009; Revised April 14, 2010; Published May 19, 2010; Online May 19, 2010

The concept of slip length, related to surface velocity and shear rate, is often used to analyze the slip surface property for flow in micro- or nanochannels. In this study, a hybrid scheme that couples molecular dynamics simulation (used near the solid boundary to include the surface effect) and a continuum solution (to study the fluid mechanics) is validated and used for the study of slip length behavior in the Couette flow problem. By varying the height of the channel across multiple length scales, we investigate the effect of channel scale on surface slip length. In addition, by changing the velocity of the moving-solid wall, the influence of shear rate on the slip length is studied. The results show that within a certain range of the channel heights, the slip length is size dependent. This upper bound of the channel height can vary with the shear rate. Under different magnitudes of moving velocities and channel heights, a relative slip length can be introduced, which changes with channel height following a logarithmic function, with the coefficients of the function being the properties of the fluid and wall materials.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 4

Velocity profiles comparisons between pure MD simulation and the hybrid scheme for group A (ρw/ρ=1, σw/σ=1, and ϵw/ϵ=0.6); the moving velocity of the bottom wall was Uw=−1.0στ−1

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Figure 1

Computational domain of Couette flow by MD: the filled circles represent solid molecules of the wall material; the hollow circles are fluid molecules

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Figure 2

Computational domain and scheme of the hybrid method: the dashed-line area is the continuum region (C) and the circled-atom area is the MD region (P). The overlapped region is bounded within two interfaces. And the molecules inside this region are driven by the external forcing field from Eq. 11.

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Figure 3

Velocity profile comparisons for group A (no-slip boundary condition, ρw/ρ=1, σw/σ=1, and ϵw/ϵ=0.6) and group B (slip boundary condition, ρw/ρ=4, σw/σ=0.75, and ϵw/ϵ=0.6) using pure MD simulations.

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Figure 5

Absolute slip length (Ls) for different moving velocities from pure MD Simulation and the hybrid scheme

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Figure 6

Relative slip length (Ls/H) for different moving velocities by using pure MD simulation and the hybrid scheme: (a) Ls/H versus H/σ; (b) log(Ls/H) versus log(H/σ)

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