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Effective mixing in a microfluidic oscillator using an impinging jet on a concave surface

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Abstract

In this study, we present a microfluidic oscillator design that employs an impinging jet on a concave surface to enhance the microscale mixing process. The Coandă effect along with the Görtler instability proves to incite sustainable flapping motion beyond the obstacle and mixing is profoundly improved. From the flow visualization results, four different regimes are identified and we find that the primary enhancement of mixing performance is always linked to the transition of flow regime. Moreover, incorporating a sudden-expansion confluence provokes flow three dimensionality and elevates the mixing level significantly at low Reynolds numbers. For a Reynolds number as low as 70, the tail flow behind the concave obstacle successfully exhibits a periodic oscillation and Hopf bifurcation is induced, leading to a drastic augmentation in the time-average mixing efficiency. By utilizing the spectrum analysis, the characteristic frequency of flapping motion is found to vary linearly with the throat velocity, resulting in a constant Strouhal number of 3.8 × 10−5.

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Abbreviations

C :

Normalized concentration

d t :

Hydraulic diameter of the throat

f :

Characteristic frequency

h :

Distance between the inlet of the diverging section and the center of the concave circle

I :

Total frame count of micrograph

i :

Time index

J :

Total number of pixels in the evaluation area

j :

Spatial index

l :

Arc length of the concave surface

\( \overline{\text{ME}} \) :

Time-averaged mixing efficiency

ME i :

Mixing efficiency for frame i

N :

Nodes

n :

Connectivity of the flow section

P :

Non-dimensional pressure

r :

Radius of curvature of the concave surface

r c :

Radius of the rounded edge of the concave surface

Re :

Reynolds number, Re = ρud t/μ

S :

Saddles

St :

Strouhal number, St = fd t/u

t :

Non-dimensional time

u :

Throat velocity

u :

Non-dimensional velocity vector

W :

Width of the confluence

ρ :

Density

μ :

Dynamic viscosity

σ :

Standard deviation

′:

Half

avg:

Average

c:

Critical

ideal:

Ideal

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Acknowledgments

This work is supported by the National Science Council of Taiwan under Grant number NSC 96-2221-E-011-100-MY3.

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Authors and Affiliations

  1. Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Sec. 4 Keelung Rd., Taipei, 106, Taiwan

    Chen-li Sun & Chia-Yin Sun

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  1. Chen-li Sun
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  2. Chia-Yin Sun
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Correspondence to Chen-li Sun.

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Sun, Cl., Sun, CY. Effective mixing in a microfluidic oscillator using an impinging jet on a concave surface. Microsyst Technol 17, 911–922 (2011). https://doi.org/10.1007/s00542-010-1177-7

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