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TECHNICAL PAPERS

Dielectrophoretic Control of Bubble Transport in Mesochannels— Experimental Study

[+] Author and Article Information
C. Helberg, J. E. Bryan

Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, MO 65211

J. Fluids Eng 129(9), 1131-1139 (Apr 04, 2007) (9 pages) doi:10.1115/1.2754310 History: Received August 09, 2005; Revised April 04, 2007

Using electrostatic fields to manipulate and/or pump fluids on the microscale is a promising method for the advancement in microfluidics. Preliminary analysis showed that unidirectional bubble motion could be achieved if the polarization (dielectrophoretic) force could overcome surface tension and viscous forces. Results are presented for the development and fundamental study of dielectrophoretic control of bubble transport in mesochannels. Electrode array configurations were manufactured using printed circuit board technology and mated with an acrylic channel. Bubble velocity, acceleration, and deformation were investigated for a range of bubble sizes, two electrode array configurations, two working fluids—pentane and a 20/80 mixture by mass of ethanol and pentane, two switching frequencies, and a range of +DC pulse applied voltages. A maximum average velocity of 6.6mms and a maximum local velocity of 30mms were achieved. For the results presented, both the switching frequency and bubble size affected the velocity for a given applied voltage. Of the two fluids tested, there was no measurable difference in the bubble velocity even though the bubble deformation was significantly different for the two fluids. It was concluded that bubble deformation reduced the unidirectional bubble motion effectiveness. Bubble deformation could be reduced by lowering the applied voltage without significantly reducing the velocity of the bubble.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Simple electrode geometry to evaluate the potential of bubble motion due to DEP (polarization) force

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Figure 2

Graphs showing the effect of DEP force on three fluids: (a) bubble velocity as function of constant applied DEP force and (b) resulting Joule heating as a function of constant applied voltage

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Figure 3

Experimental system to study electrostatic force control in small scale fluidic phenomena: (a) test system and (b) test card support

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Figure 4

The measured voltage during one sequence at 1Hz pulse to a four-pair electrode array configuration (EAC)

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Figure 5

Photographs and drawings of EAC 1 and EAC 2; top pictures show test card with the corresponding electrode array; middle drawing is the electrode array with dimensions in millimeter; and the bottom is the image field of view from the high-speed camera.

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Figure 6

Bubble deformation and motion in EAC 1: (a) bubble deformation with and without an applied field for pentane (top) and the 20/80 mixture (bottom) and (b) image sequence of induced bubble motion in pentane

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Figure 7

Bubble deformation and motion in EAC 2: (a) bubble deformation with and without an applied field for pentane (top) and the 20/80 mixture (bottom) and (b) image sequence of induced bubble motion in pentane

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Figure 8

Graph of the average velocity through the field of view versus applied voltage for EAC 1

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Figure 9

Comparison of interface velocity, interface acceleration, and normalized bubble deformation averaged over three trials for a midsize bubble (∼5.5mm) at 1Hz switching frequency and 2.1kV applied voltage in pentane: (a) results for EAC 1 and (b) results for EAC 2

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Figure 10

Average velocity through field of view for different bubble sizes at 2.1kV DC voltage pulse for different conditions: (1) frequency of 0.4Hz and 1Hz, (2) EAC 1 and EAC 2, and (3) pentane and the 20/80 mixture

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