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Research Papers: Multiphase Flows

Characteristics of Transient Electroosmotic Flow in Microchannels With Complex-Wavy Surface and Periodic Time-Varying Electric Field

[+] Author and Article Information
Ching-Chang Cho

Department of Mechanical Engineering,
National Cheng Kung University,
Tainan 70101, Taiwan, Republic of China

Chieh-Li Chen

Department of Aeronautics and Astronautics,
National Cheng Kung University,
Tainan 70101, Taiwan, Republic of China

Cha'o-Kuang Chen

Department of Mechanical Engineering,
National Cheng Kung University,
Tainan 70101, Taiwan, Republic of China
e-mail: ckchen@mail.ncku.edu.tw

1Corresponding author.

Manuscript received June 14, 2011; final manuscript received October 5, 2012; published online March 19, 2013. Assoc. Editor: Kendra Sharp.

J. Fluids Eng 135(2), 021301 (Mar 19, 2013) (11 pages) Paper No: FE-11-1250; doi: 10.1115/1.4023441 History: Received June 14, 2011; Revised October 05, 2012

A numerical investigation is performed into the flow characteristics of the electroosmotic flow induced within a microchannel with a complex-wavy surface by a time-varying periodic electric field. The simulations focus specifically on the effects of the Strouhal number of the periodic electric potential, the amplitude of the periodic electric potential, the amplitude of the complex-wavy surface, and the waveform geometry. The results show that under steady-time periodic conditions, the flow pattern induced within the microchannel varies over the course of the oscillation period. In particular, it is shown that a flow recirculation structure is generated in the trough region of the wavy surface as the applied electric field falls to zero if the amplitude of the wavy surface exceeds a certain threshold value. In addition, it is shown that the phases of the electric field and electroosmotic velocity near the wall surface are almost identical. However, a phase shift exists between the electric field and the bulk flow velocity in the central region of the channel; particularly at larger values of the Strouhal number. Finally, it is shown that the velocity profile near the wavy surface is more sensitive to changes in the waveform geometry than that in the center of the channel. Overall, the simulation results presented in the study provide a useful source of reference for the development of new microfluidic systems incorporating microchannels with complex-wavy surfaces.

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Figures

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Fig. 1

Schematic illustration of microchannel with complex-wavy surface. Note that point Pwt and Pwc indicate the wave trough and wave crest, respectively. Note also that for the discussions presented in the study, the wave trough and the wave crest take at x* = 0.17 and x* = 0.83, respectively.

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Fig. 2

Comparison of exact and numerical solutions for time-periodic velocity profiles in a parallel-plate microchannel

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Fig. 3

Comparison of numerical results (a) and experimental results (b) presented in Ref. [33] for combined electroosmotic flow and pressure-driven flow in a microchannel with plane upper wall and sinusoidal lower wall. Note that the electroosmotic flow is from right to left, while the pressure-driven flow is from left to right.

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Fig. 4

Flow field distributions in complex-wavy surface microchannel with wave amplitude of α1 = 0.15 at (a) t* = 5.0, (b) t* = 5.25, (c) t* = 5.50, and (d) t* = 5.75. Note that St = 1.0, αp = 1.0 and Rα = 12.5.

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Fig. 5

u-velocity profiles in (a) wave trough region and (b) wave crest region of complex-wavy surface microchannel with wave amplitude of α1 = 0.15. Note that St = 1.0, αp = 1.0 and Rα = 12.5.

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Fig. 6

(a) Variation of electric field intensity along complex-wavy wall surface and (b) evolution over time of electric fields in wave crest and wave trough regions of wavy surface. Note that α1 = 0.15, St = 1.0, αp = 1.0 and Rα = 12.5. Note also that E* and E0 are the nondimensional electric field and reference electric field, respectively.

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Fig. 7

Evolution of u-velocity profile and electric field distribution over time for Strouhal numbers of: (a) St = 0.1, (b) St = 1.0, and (c) St = 10.0. Note that α1 = 0.15, αp = 1.0 and Rα = 12.5. Note also that in the figures, St = 0 indicates that a constant time-independent electric potential is applied to the microchannel.

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Fig. 8

Evolution of volumetric flow rate over time for various Strouhal numbers. Note that α1 = 0.15, αp = 1.0 and Rα = 12.5.

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Fig. 9

Evolution of u-velocity profile as function over time in (a) wave trough region and (b) wave crest region of wavy channel given different amplitudes of oscillating electric potential. Note that α1 = 0.15, St = 1.0 and Rα = 12.5.

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Fig. 10

Evolution of volumetric flow rate over time for various amplitudes of oscillating electric potential. Note that α1 = 0.15, αp = 1.0 and Rα = 12.5.

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Fig. 11

Evolution of electric field profile over time given complex-wavy surfaces with different amplitudes. Note that St = 1.0, αp = 1.0 and Rα = 12.5.

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Fig. 12

Evolution of u-velocity profile over time in (a) wave trough region and (b) wave crest region of complex wavy-surface microchannels with different wave amplitudes. Note that St = 1.0, αp = 1.0 and Rα = 12.5.

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Fig. 13

u-velocity profiles in wave trough region of complex wavy-surface microchannels with different wave amplitudes at time t* = 5.75. Note that St = 1.0, αp = 1.0 and Rα = 12.5.

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Fig. 14

Evolution of volumetric flow rate over time for various wave amplitudes. Note that St = 1.0, αp = 1.0 and Rα = 12.5.

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Fig. 15

Variation of electric field intensity along wavy surfaces with different waveforms at time t* = 5.25. Note that St = 1.0 and αp=1.0.

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Fig. 16

Variation of u-velocity profiles along (a) wavy surface and (b) channel center of complex wavy-surface microchannels with different geometric waveforms at time t* = 5.25. Note that St = 1.0 and αp = 1.0.

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