Abstract
The flow of a compressible, isothermal gas under slightly rarefied conditions in a 2D planar geometry is considered. The gas is shear driven and is also subject to an applied pressure gradient, which is also known as Couette–Poiseuille (CP) flow. In this paper, the full Navier-Stokes (NS) equations are solved using a perturbation expansion up to the first order. The pressure profile is solved numerically. On the basis of the solutions, effects of rarefaction and compressibility on the flow characteristics are investigated in detail. The results show the parallel flow assumption to be invalid for cases with slight rarefaction. The axial and vertical velocity components are found to depend on the degree of rarefaction, applied pressure gradient and wall velocity. The effects of rarefaction on the occurrence of back flow are also discussed. In addition, the results for the Poiseuille and CP flow with and without rarefaction can be easily obtained from our results.
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Abbreviations
- H :
-
microchannel height
- K n :
-
Knudsen number
- K o :
-
outlet Knudsen number
- L :
-
microchannel length
- M :
-
Mach number
- p :
-
pressure
- P :
-
pressure ratio of inlet to outlet
- R :
-
Reynolds number
- T :
-
temperature
- u :
-
streamwise velocity
- u w :
-
wall velocity
- υ:
-
vertical velocity
- α:
-
parameter for simplicity, α = (ɛ R)/(γ M 2)
- γ:
-
ratio of specific heat
- ɛ:
-
ratio of channel height to length (perturbation parameter)
- μ:
-
viscosity
- ρ:
-
density
- σ:
-
streamwise momentum accommodation factor, σ = (2 − σ m ) /σ m
- σ m :
-
tangential momentum accommodation coefficient
- ℜ:
-
ideal gas constant
- o:
-
outlet
- 0,1:
-
orders for perturbation solution
- \(\widetilde{{}}\) :
-
nondimensional symbol
- \(\bar{{}} \) :
-
area average symbol at outlet
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Acknowledgments
The authors are very grateful for the support of Natural Science Foundation of China under Grant No. 10472054 and SRFDP under Grant No. 20040003070.
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Zahid, W.A., Yin, Y. & Zhu, KQ. Couette–Poiseuille flow of a gas in long microchannels. Microfluid Nanofluid 3, 55–64 (2007). https://doi.org/10.1007/s10404-006-0108-5
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DOI: https://doi.org/10.1007/s10404-006-0108-5