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TECHNICAL PAPERS

A Microfluidic Mixer Utilizing Electrokinetic Relay Switching and Asymmetric Flow Geometries

[+] Author and Article Information
Yiou Wang, Jiang Zhe, Benjamin T. Chung

Department of Mechanical Engineering,  The University of Akron, Akron, OH 44325

Prashanta Dutta

School of Mechanical and Materials Engineering,  Washington State University, Pullman, WA 99164-2920dutta@mail.wsu.edu

J. Fluids Eng 129(4), 395-403 (Jun 29, 2006) (9 pages) doi:10.1115/1.2436578 History: Received February 03, 2006; Revised June 29, 2006

Performances of a hybrid electrokinetic-passive micromixer are predicted numerically. An h/p-type spectral element method is used to simulate the mixing behavior in microdevices. The numerical algorithm employs modal spectral expansion in quadrilateral and unstructured triangular meshes and provides high-order numerical accuracy. A second-order accurate, stiffly stable integration scheme is used for temporal integration. In the numerical technique, the electric double layer is not resolved to avoid expensive computation, rather a slip velocity is assigned at the channel surface based on the electric field and the electroosmotic mobility. The presented hybrid mixing scheme takes advantages of mixing enhancements induced by asymmetric flow geometries and electrokinetic relay actuation. Effects of relay frequency, applied electric potential, channel width, and channel geometry on micromixing have been conducted. Numerical results show that electrokinetic relay at an appropriate frequency causes effective mixing. Moreover, asymmetric flow geometries and narrow channel width are critical for ultraeffective mixing. The proposed hybrid mixing scheme not only provides excellent mixing within very short time, but also can easily be integrated with microdevices for “lab-on-a-chip” applications because there is no need of any external mechanical pumps.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of (a) electrokinetic relay micromixer and (b) hybrid (electrokinetic asymmetric structure) micromixer

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Figure 2

Effects of microchannel width on mixing efficiency at the micromixer outlet (x=1000μm) under different relay frequencies for ϕa=20V and ϕs=20V: Case (a)Pe=510, W=50μm; (b)Pe=1028, W=100μm; and (c)Pe=3208, W=300μm

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Figure 3

Concentration contour for three electrokinetic micromixers presented in Fig. 2, under three relay frequencies (a)f=0Hz(b)f=5Hz, and (c)f=10Hz. Mixing performances are presented 2s after the initiation of electric field.

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Figure 4

Mixing efficiency for electrokinetic relay micromixer (a) at the micromixer outlet (x=1000μm); (b) at an intermediate location (x=300μm) under different relay frequencies. Here, ϕs=20V, ϕa=20V, and Pe=510.

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Figure 5

Average mixing efficiency at the micromixer outlet for different electroosmotic relay frequency. Here ϕs=20V and ϕa=20V. The error bars indicate the oscillation range of the mixing efficiency. The data points on the curves are the average values calculated by integrating mixing efficiency over a relay cycle. The optimum frequency for 50μm, 100μm, and 300μm wide micromixers are 8Hz, 5Hz, and 3.3Hz, respectively.

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Figure 6

Mixing efficiency variation with Strouhal number (St). For the current micromixer (θ=30deg), the optimum efficiency takes place at St≈0.5.

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Figure 7

Effects of applied electric potential on mixing efficiency (a) at the micromixer outlet (x=1000μm) and (b) at an intermediate location (x=300μm) under different relay frequencies. Here, Pe=510.

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Figure 8

Concentration contour for (a) the hybrid micromixer and (b) the electrokinetic micromixer at different times. The corresponding micromixer design is presented in Figs.  11, respectively. Here, ϕs=20V, ϕa=20V, and Pe=262 and 510 for the electrokinetic and hybrid micromixers, respectively.

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Figure 9

Comparison of mixing efficiency (a) at the micromixer outlet (x=1000μm) and (b) at an intermediate location (x=300μm) with and without asymmetric serpentine structures. Here, ϕs=20V and ϕa=20V. The Peclet numbers for the electrokinetic and hybrid micromixers are 510 and 262, respectively.

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