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Research Papers

Using Direct Simulation Monte Carlo With Improved Boundary Conditions for Heat and Mass Transfer in Microchannels

[+] Author and Article Information
J. Yang, J. Y. Zheng

P. Tang Institute of Chemical Engineering Process and Machinery, Zhejiang University, Hangzhou 310027, China

J. J. Ye1

P. Tang Institute of Chemical Engineering Process and Machinery, Zhejiang University, Hangzhou 310027, Chinazdhjkz@zju.edu.cn

I. Wong

Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, Los Angeles, CA 90095

C. K. Lam

Department of Mechanical Engineering, University of California, Berkeley, Berkeley, CA 94704

P. Xu

School of Aeronautics and Astronautics, Zhejang University, Hangzhou 310027, China

R. X. Chen, Z. H. Zhu

 Zhejang Chengxin Pharm&Chem Equipment Co. Ltd., Taizhou 318012, China

1

Corresponding author.

J. Heat Transfer 132(4), 041008 (Feb 19, 2010) (9 pages) doi:10.1115/1.4000880 History: Received January 01, 2009; Revised June 24, 2009; Published February 19, 2010; Online February 19, 2010

Micro-electromechanical systems and nano-electromechanical systems have attracted a great deal of attention in recent years. The flow and heat transfer behaviors of micromachines for separation applications are usually different from that of macro counterparts. In this paper, heat and mass transfer characteristics of rarefied nitrogen gas flows in microchannels are investigated using direct simulation Monte Carlo with improved pressure boundary conditions. The influence of aspect ratio and wall temperature on mass flowrate and wall heat flux in microchannels are studied parametrically. In order to examine the aspect ratio effect on heat and mass transfer behaviors, the wall temperature is set constant at 350 K and the aspect ratio of the microchannel varies from 5 to 20. The results show that as the aspect ratio increases, the velocity of the flow decreases, so does the mass flowrate. In a small aspect ratio channel, the heat transfer occurs throughout the microchannel; as the aspect ratio of the microchannel increases, the region of thermal equilibrium extends. To investigate the effects of wall temperature (Tw) on the mass flowrate and wall heat flux in a microchannel, the temperature of the incoming gas flow (Tin) is set constant at 300 K and the wall temperature varies from 200 K to 800 K while the aspect ratio is remained unchanged. Results show that majority of the wall heat flux stays within the channel entrance region and drops to nearly zero at the halfway in the channel. When Tw<Tin, under the restriction of pressure-driven condition and continuity of pressure, the molecular number density of the flow decreases along the flow direction after a short increase at the entrance region. When Tw>Tin, the molecular number density of the flow drops rapidly near the inlet and the temperature of the gas flow increases along the channel. As Tw increases, the flow becomes more rarefied, the mass flowrate decreases, and the resistance at the entrance region increases. Furthermore, when Tw>Tin, a sudden jump of heat transfer flux and temperature are observed at the exit region of the channel.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 11

Molecular number density distributions at different Tw

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Figure 12

Distributions of the centerline velocity at different Tw

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Figure 13

Effect of the Tw on the mass flowrate

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Figure 14

Distributions of centerline temperature at different Tw

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Figure 15

Distributions of temperature jump at different Tw

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Figure 9

Wall heat flux distributions along the microchannel at different AR

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Figure 10

Effect of Tw on pressure distributions along the channel

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Figure 2

Sketch of the microchannel with two parallel plates

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Figure 3

Result comparison between our new method and Pong’s experimental data

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Figure 4

Pressure distributions along the centerline of the microchannel at different AR

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Figure 5

Kn number distributions along the microchannel at different AR

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Figure 6

Effect of AR on the velocity distributions in the microchannel: (a) streamwise velocity magnitude contours and (b) velocity distributions along the centerline

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Figure 7

Effects of the AR on mass flowrate

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Figure 8

Temperature distributions along the centerline of the microchannel at different AR

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Figure 16

Wall heat flux distributions at different Tw

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Figure 1

Scanning electron microscope images of filters: (a) Whatman alumina filter (anodisc) and (b) microfabricated membrane filters

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