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Unsteady flow behaviors in an obstacle-type valveless micropump by micro-PIV

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Abstract

In this paper, a PZT micropump excited by amplified squarewave signals with various frequencies was used to study the transient flow behaviors in an obstacle-type valveless micropump. A micro-particle-image-velocimetry (micro-PIV) with an external trigger was developed to obtain flow fields at the outlet and around the obstacle with various phases in a cycle. In comparison with previous studies on the pump performance, such as pump pressure and volume flow rate, more detailed information about the pump was obtained. The velocity profiles and periodic sectional mean velocities exhibited the unsteady flow nature. The total net flow generation efficiency per cycle was obtained experimentally by integrating the phase-dependent velocities. The flow recirculation around the obstacle was observed and quantified to investigate the influence on the pump performance. The duration, circulation, and the size of the recirculation regions indicated that this flow behavior could enhance the flow-directing capability. These results are very useful for the design and improvement of obstacle-type valveless micropumps.

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Abbreviations

A o :

Area of grid cell (mm2)

d :

Diameter of a glass tube

d p :

Diameter of seeding particle (μm)

D f :

Diffusion coefficient (m2/s)

h :

Height of liquid in a glass tube

I :

Fluid inductance (Pa s2/m3)

n :

Radial oscillating frequency

n o :

Refraction ratio

NA :

Numerical aperture

\({{{\hat{\bf Q}}}}\) :

Volume of flow rate (m3/s)

r :

Characteristic length of channel (μm)

R :

Flow resistance (Pa s/m3)

t :

Specific time in a time period (s)

t r :

Response time of tracer particle (s)

T :

Time of a period (s)

u i :

Velocity in x or y direction (mm/s)

U o :

Maximum velocity at each velocity profile (mm/s)

Wo:

Womersley number

Y o :

Channel width (μm)

\({{{\hat{\bf Z}}}}\) :

Complex form of flow impedance (Pa s/m3)

δz o :

Depth of correlation (μm)

\(\Delta {{{\hat{\bf P}}}}\) :

Complex form of pressure drop (Pa)

Δt :

Time interval between the laser pulses (s)

ɛ i :

Errors due to Brownian motion

Γ:

Circulation (mm2/s)

η:

The flow-directing efficiency of a valveless flow rectifier

η o :

Flow rate ratio of pump/supply phases in a obstacle-type micropump

ξdiffuser :

Flow resistance coefficient in diffuser direction

ξnozzle :

Flow resistance coefficient in nozzle direction

λ:

Wavelength of exciting light source (nm)

μ f :

Viscosity of fluid (N s/m2)

ν f :

Kinematic viscosity of fluid (m2/s)

ρ f :

Density of fluid (kg/m3)

ρ p :

Density of tracer particle (kg/m3)

ω z :

Vorticity in z direction (1/s)

θ:

Collection angle

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Acknowledgments

This work was supported by Ministry of Economic Affairs, 96-EC-17-A-05-A1-0017, and National Science Council of Taiwan, NSC 95-2218-E-002-051-MY3, R.O.C.

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Authors and Affiliations

  1. Institute of Applied Mechanics, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, 106, Taiwan, ROC

    H. J. Sheen, C. J. Hsu, T. H. Wu, C. C. Chang, H. C. Chu & U. Lei

  2. Department of Automatic Control Engineering, Chungchou Institute of Technology, 6, Lane 2, Sec. 3, Shanchiao Rd.,Yuanlin, Changhua, 51003, Taiwan, ROC

    C. Y. Yang

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  1. H. J. Sheen
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  2. C. J. Hsu
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  3. T. H. Wu
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  4. C. C. Chang
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  5. H. C. Chu
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  6. C. Y. Yang
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  7. U. Lei
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Correspondence to H. J. Sheen.

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Sheen, H.J., Hsu, C.J., Wu, T.H. et al. Unsteady flow behaviors in an obstacle-type valveless micropump by micro-PIV. Microfluid Nanofluid 4, 331–342 (2008). https://doi.org/10.1007/s10404-007-0189-9

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  • DOI: https://doi.org/10.1007/s10404-007-0189-9

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