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Research Papers: Flows in Complex Systems

Evaluation of the Mixing Performance of the Micromixers With Grooved or Obstructed Channels

[+] Author and Article Information
Yeng-Yung Tsui1

Department of Mechanical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan R.O.C.yytsui@mail.nctu.edu.tw

Ching-Shiang Yang, Chung-Ming Hsieh

Department of Mechanical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan R.O.C.

1

Corresponding author.

J. Fluids Eng 130(7), 071102 (Jun 25, 2008) (10 pages) doi:10.1115/1.2948364 History: Received May 17, 2007; Revised April 23, 2008; Published June 25, 2008

The mixing flows in microchannels were examined using numerical methods. To speed up fluid mixing, it is essential to generate lateral transport of mass. In this study, the mixing flow is disrupted by either placing grooves or block obstacles on the walls of the channels. Since the grooves or the blocks appear in a periodic configuration, the velocity is solved only in a section of the channel. With the repeating cycle of flow velocity field, the fluid concentration can be calculated throughout the entire length of the channel. Good agreement with experiments in the mixing performance justifies the present methodology. Two different channel configurations are under consideration: grooved channels and obstructed channels. The results reveal that with straight grooves, a well organized vortex flow is formed in the vertical plane along the groove, which leads to a helical flow in the channel. The mixing performance can be enhanced by having grooves on both the top and the bottom walls arranged in a staggered manner, by which the transversal velocity is largely increased. It is seen that the strength of the secondary flow and, thus, the mixing can be improved by suitably choosing geometric parameters of the groove, such as the depth, the width, and the oblique angle. It is also shown that the efficient mixing for the staggered herringbone type groove is due to the fluid stratification caused by the exchange of position of the resulted counter-rotating vortices. As for the obstructed channels, the flows are in essence two dimensional. Very strong transversal velocity can be produced by narrowing down the flow passage in the channel. However, the efficient mixing is obtained at the cost of large pressure head loss.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic drawings of the considered micromixers: (a) SGM, (b) DSGM, (c) SHM, (d) Block Type 1, and (e) Block Type 2

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Figure 2

Typical grid layouts used for (a) SGM and (b) SHM

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Figure 3

Comparison of the predicted mixing indices with experiments using different meshes for (a) SGM and (b) SHM

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Figure 4

Secondary velocity fields in cross sections for (a) SGM, (b) DSGM, and (c) SHM. The Planes A and A′ are referred to Fig. 1.

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Figure 5

Visualization of the concentration distribution in the y‐z plane at different cycles for (a) SGM, (b) DSGM, and (c) SHM. Note that the length of a cycle for a SHM is longer than that for the SGM and DSGM.

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Figure 6

Secondary velocity vectors in Planes B and C for the SGM. Plane B is a transversal plane in the middle of a groove and Plane C is located in the middle of a ridge. The locations of the planes are referred to Fig. 1. These planes are projected onto the y‐z plane

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Figure 9

Comparison of mixing performance for (a) different groove depths, (b) different groove widths, and (c) different oblique angles for the SGM

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Figure 10

Comparison of the transversal velocity along the vertical line in the center of Plane B and Plane C for different oblique angles. This transversal velocity is the component in the groove direction and is normalized by the inlet velocity U¯.

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Figure 11

Four types of block obstacles used in the obstructed microchannels

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Figure 12

Comparison of mixing performance for different block types: (a) Pe=2×105 and (b) Pe=2×103

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Figure 13

Velocity field in the x‐y plane at mid height of the channel for Block Types 1 and 2 at Pe=2×105

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Figure 14

Concentration field in the x‐y plane at mid height of the channel for the four block types

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Figure 15

Dimensionless pressure loss along the channel for all considered micromixers at Re=1(Pe=2×105)

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Figure 7

Concentration filed in the x‐y plane at mid height of the channel for the SHM

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Figure 8

Comparison of mixing performance for the SGM, DSGM, and SHM

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