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TECHNICAL PAPERS

DSMC Simulation of Subsonic Flows in Parallel and Series Microchannels

[+] Author and Article Information
M. Le, N. Esmail

Department of Mechanical and Industrial Engineering, Concordia University, Montreal, QC, H3G 1M8 Canada

I. Hassan1

Department of Mechanical and Industrial Engineering, Concordia University, Montreal, QC, H3G 1M8 CanadaIbrahimH@alcor.concordia.ca

1

Author to whom correspondence should be addressed.

J. Fluids Eng. 128(6), 1153-1163 (May 08, 2006) (11 pages) doi:10.1115/1.2354525 History: Received September 06, 2005; Revised May 08, 2006

Flows in uniform, parallel, and series microchannels have been investigated using the direct simulation Monte Carlo (DSMC) method. For the uniform microchannel cases, at higher pressure ratio, mixed Kn-regime flows were observed, where the Knudsen number (Kn) varies from below 0.1 to above 0.1. Also, the higher pressure ratio makes the flow accelerate more as the flow develops through the uniform microchannel. In order to examine the heat transfer characteristics between the wall and the bulk flow, a linear temperature distribution was imposed on the wall. Most of the wall heat flux occurs within the channel entrance region while it remains a constant with a slight magnitude along the rest of the channel wall. For the series microchannel cases, the computational domain was established by adding three surfaces and excluding one region from the rectangular domain. Diffuse effects were observed near the interface of the two segments, where the flow upstream the interface can be either heated or cooled by the flow downstream depending on their temperature difference. In addition, the effect of the gas species was investigated by conducting the simulation using helium and argon respectively. It can be found that the speed of the gas with lighter molecular mass is much higher than that of the heavier gas. The computational domain of the parallel microchannel was established similarly to that of the series microchannel. Under a certain pressure ratio, more pressure drop occurs in the parallel parts as the gap height increases. The recirculation phenomenon was observed after the gap wall between the two parallel parts and was evaluated quantitatively in the present study by defining a parameter called the developing coefficient. The gap height between the two parallel parts has only slight effect of the flow development.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

(a) Schematic of the uniform microchannel geometry, (b) Schematic of the series microchannel geometry, and (c) Schematic of the parallel microchannel geometry

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Figure 2

(a) Boundary conditions for the series microchannel flow and (b) Boundary conditions for the parallel microchannel flow

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Figure 3

Mesh size effect on (a) the pressure distribution along the uniform channel and (b) the streamwise velocity profiles at the channel midspan

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Figure 4

(a) Effect of the average number of simulated particles per cell on the pressure and centerline temperature distributions and (b) Effect of the average number of simulated particles per cell on velocity profiles at channel inlet, midspan, and outlet

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Figure 5

Pressure distribution along the uniform microchannel for Knin=0.0547 and Pin∕Pout=4

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Figure 6

Velocity profiles corresponding to different local Knudsen numbers in uniform microchannel

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Figure 7

Wall heat flux distribution for flow in uniform microchannels with Tw=500K

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Figure 8

Wall temperature jump for flow in uniform microchannels

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Figure 9

Kn number distribution along the uniform channel for Pin∕Pout=4, 2, and 1.33

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Figure 10

Mach number distribution along the centerline of the uniform microchannel for Pin∕Pout=4, 2 and 1.33

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Figure 11

Wall heat flux for cases with linear wall temperature distribution

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Figure 12

Temperature distribution of the flow close to the wall

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Figure 13

Velocity vectors for series microchannel flow at Pin∕Pout=4 and Knin=0.0912

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Figure 14

Pressure distribution for the series microchannel flow coming from difference edges at Pin∕Pout=4

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Figure 15

Wall heat flux for the series microchannel flows with different wall temperature distributions

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Figure 16

Temperature profiles at (a)x∕L=0.25, (b)x∕L=0.36, (c)x∕L=0.38, and (d)x∕L=0.60

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Figure 17

Velocity profiles at x∕L=0.431 for (a)Pin∕Pout=2, (b)Pin∕Pout=4, (c)Pin∕Pout=6, and (d)Pin∕Pout=8

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Figure 18

Velocity vectors of the parallel microchannel flow at Pin∕Pout=4 and Knin=0.182

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Figure 19

Evolution of the relative density difference

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Figure 20

Effect of the gap size on the developing coefficient

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Figure 21

Wall pressure distribution along the parallel microchannel with different gap sizes

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Figure 22

Effect of the gas size on the mass flow rate at Pin∕Pout=4

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