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Research Papers

Microfluidic Bubble Generation by Acoustic Field for Mixing Enhancement

[+] Author and Article Information
Shasha Wang

Xiaoyang Huang1

Chun Yang

 School of Mechanical and Aerospace Engineering,Nanyang Technological University, 639798, Singaporemcyang@ntu.edu.sg

1

Corresponding author.

J. Heat Transfer 134(5), 051014 (Apr 13, 2012) (4 pages) doi:10.1115/1.4005705 History: Received April 27, 2010; Revised December 07, 2010; Published April 11, 2012; Online April 13, 2012

We demonstrate the bubble generation in a microfluidic channel by both experimental observation and numerical simulations. The microfluidic channel contains a nozzle-shaped actuation chamber with an acoustic resonator profile. The actuation is generated by a piezoelectric disk below the chamber. It was observed that for a steady deionized (DI) water flow driven through the channel, bubbles occurred in the channel when the piezoelectric disk was actuated at frequencies between 1 kHz and 5 kHz. Outside this actuation frequency range, no bubble generation was observed in the channel. The experiment showed that the presence of bubbles in this frequency range could significantly enhance the fluid mixing in the microfluidic channel, which otherwise would not happen at all without the bubbles. To further understand the bubble generation, the flow field in the microchannel was numerically simulated by a two-dimensional model. The numerical results show that there is a low pressure region inside the actuation chamber where water pressure is below the corresponding vapor pressure and thus bubbles can be generated. The bubble generation was also experimentally observed in the microchannel by using a high speed camera.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic illustration of the acoustic microfluidic mixer. (a) Side view of the mixer configuration; (b) top view of the mixer; (c) visualization of fluorescent dye in mixing experiment before powering on the piezoelectric disk.

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Figure 2

Visualization distributions of fluorescent dye in the mixer under various applied frequencies. The experimental images are taken from the region indicated by the dashed line rectangle in Fig. 1. Arrows show the location of acoustically induced gas bubbles at frequencies between 1 kHz and 5 kHz. Flow is laminar without bubbles at frequency 0.5 kHz and 10 kHz.

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Figure 3

The computed absolute pressure distributions at (a) frequency of 1 kHz, t = 0.643T, the pressure in the low pressure region is 2990 Pa; (b) frequency of 1.5 kHz, t = 0.557T, the pressure in the low pressure region is 380 Pa; (c) frequency of 2 kHz, t = 0.535T, the pressure in the low pressure region is 1290 Pa; (d) frequency of 5 kHz, t = 0.5078T, the pressure in the low pressure region is 3000 Pa

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Figure 4

Experimental setup for observing bubble generation using a high speed camera

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Figure 5

Different stages of the bubbles generation processes in the mixing channel, working fluid is degassed DI water; (a) top view of the mixer region indicated by the dashed rectangle in Fig. 1; (b) the image for zone 1 without bubbles before the actuation; (c) the initial bubbles occur in zone 1 at 0.02 s after the actuation, recorded at 10,000 frames per second; (d) the bubbles in zone 2 at t = 0.6 s after the actuation, recorded at 3000 frames per second; (e) and (f) the collision and coalescence of bubbles in zone 3 at 1.5 s after the actuation recorded at 20,000 frames per second. The actuation frequency is at 1.0 kHz.

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