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Research Papers: Flows in Complex Systems

Mixing Enhancement by Microrotor in Step Channel

[+] Author and Article Information
Thien X. Dinh

Department of Mechanical Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japanthien@cfd.ritsumei.ac.jp

Yoshifumi Ogami

Department of Mechanical Engineering, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu, Shiga 525-8577, Japan

J. Fluids Eng 133(2), 021101 (Feb 04, 2011) (6 pages) doi:10.1115/1.4003420 History: Received January 31, 2010; Revised December 23, 2010; Published February 04, 2011; Online February 04, 2011

In this paper, the mixing enhancement of a micromixer consisting of a step channel and a shuttlecock rotor suspended in the step is numerically analyzed. Asymptotic mixing performance is investigated as a function of Strouhal and Peclet numbers by particle tracking simulation and the Eulerian approach. The simulation results show that the rotor creates downward and inward flows in behind the rotor paddles, whereas the upward and outward flows are produced in front of the rotor paddles. At a small Strouhal number, convective mixing is very poor. However, the mixing direction is rotated by 90 deg, which can reduce the mixing time by the square of the aspect ratio of the cross section of the channel. In contrast, at a relatively large Strouhal number, good convective mixing occurs. Quantitative analysis of mixing performance of the mixer demonstrates that the mixing structures are similar for the same Strouhal number and mixing is improved with increasing Strouhal number. The mixing efficiency of the mixer decreases linearly with increasing log of the Peclet number at a relatively large Strouhal number.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

(a) The configuration of the mixer. The grayscale spectrum on the inlets indicates a typical parabolic velocity profile in a rectangular channel applied to the inlets. (b) The top and side views of the mixer with dimensions.

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Figure 2

The projected velocity field on the planes, which are (a) in front of and (b) behind the paddle of the rotor respecting to the rotation direction. The circle arrows on the top of the rotor indicate the rotation direction of the rotor. The grayscale bars represent the ratio of the magnitude of the projected velocity to ωR. The ratios are almost invariant with the rotation speed of the rotor, except that of the right plane in (b), which includes the mean velocity from the inlets to the outlet. The arrows on the considered plane represent the main flow near the paddle of the rotor.

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Figure 3

Intersection maps for St=20. (a) and (b) show the intersection maps under the bottom of the rotor for z=−5 μm and z=−1 μm, respectively. (c) and (d) show the intersection maps in the outlet channel for x=75 μm and x=100 μm, respectively.

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Figure 4

Intersection maps for St=50. (a) and (b) show the intersection maps under the bottom of the rotor for z=−5 μm and z=−1 μm, respectively. (c) and (d) show the intersection maps in the outlet channel for x=75 μm and x=100 μm, respectively.

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Figure 5

Probability density distribution of points on intersection maps at the outlet along the vertical direction (a) for St=60 and (b) for different Strouhal numbers

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Figure 6

Mixing variance coefficient computed at the outlet along the vertical direction (a) for the same St=60 and (b) for different Strouhal numbers

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Figure 7

Variation of mixing efficiency coefficient against the dimensionless resident time

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Figure 8

Variation of mixing efficiency coefficient against Peclet number for St=50

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Figure 9

Variation of mixing efficiency coefficient against Peclet number for different Strouhal numbers

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Figure 10

Comparison of mixing efficient between one-layer and two-layer designs

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