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Research Papers: Flows in Complex Systems

Experimental Analysis of Microchannel Entrance Length Characteristics Using Microparticle Image Velocimetry

[+] Author and Article Information
Tariq Ahmad

Department of Mechanical and Industrial Engineering, Concordia University, Montreal, QC, H3G 1M8, Canada

Ibrahim Hassan1

Department of Mechanical and Industrial Engineering, Concordia University, Montreal, QC, H3G 1M8, Canadaibrahimh@alcor.concordia.ca

1

Corresponding author.

J. Fluids Eng 132(4), 041102 (Apr 15, 2010) (13 pages) doi:10.1115/1.4001292 History: Received September 28, 2008; Revised February 02, 2010; Published April 15, 2010; Online April 15, 2010

The study of the entrance region of microchannels and microdevices is limited, yet important, since the effect on the flow field and heat transfer mechanisms is significant. An experimental study has been carried out to explore the laminar hydrodynamic development length in the entrance region of adiabatic square microchannels. Flow field measurements are acquired through the use of microparticle image velocimetry (micro-PIV), a nonintrusive particle tracking and flow observation technique. With the application of micro-PIV, entrance length flow field data are obtained for three different microchannel hydraulic diameters of 500μm, 200μm, and 100μm, all of which have cross-sectional aspect ratios of 1. The working fluid is distilled water, and velocity profile data are acquired over a laminar Reynolds number range from 0.5 to 200. The test-sections were designed as to provide a sharp-edged microchannel inlet from a very large reservoir at least 100 times wider and higher than the microchannel hydraulic diameter. Also, all microchannels have a length-to-diameter ratio of at least 100 to assure fully developed flow at the channel exit. The micro-PIV procedure is validated in the fully developed region with comparison to Navier–Stokes momentum equations. Good agreement was found with comparison to conventional entrance length correlations for ducts or parallel plates, depending on the Reynolds range, and minimal influence of dimensional scaling between the investigated microchannels was observed. New entrance length correlations are proposed, which account for both creeping and high laminar Reynolds number flows. These correlations are unique in predicting the entrance length in microchannels and will aid in the design of future microfluidic devices.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Top and side views of test-section configuration used in present study

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Figure 2

Experimental setup of micro-PIV system with flow loop

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Figure 3

Experimental coordinate system used in present investigation

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Figure 4

Flow separation effects produced by sharp edge corners at the entrance region of the microchannel: (a) theoretical flow pattern and (b) experimental vector flow field for the 200 μm channel at Re=50

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Figure 6

Developing velocity profiles for the 100 μm channel at Re of (a) 0.476, (b) 4.76, (c) 50, and (d) 89

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Figure 7

Developing velocity profiles for the 200 μm channel at Re of (a) 0.5, (b) 5, (c) 50, and (d) 200

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Figure 8

Developing velocity profiles for the 500 μm channel at Re of (a) 0.5, (b) 5, (c) 50, and (d) 200

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Figure 9

Centerline velocity development for the 100 μm channel at Re of (a) 0.476, (b) 4.76, (c) 50, and (d) 89

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Figure 5

Test-section microchannel inlet configuration: (a) isometric view of the microchannel entrance with the reservoir walls and (b) separation zone at section A-A for the microchannel entrance due to the nonsymmetric vena contracta effect

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Figure 10

Centerline velocity development for the 200 μm channel at Re of (a) 0.5, (b) 5, (c) 50, and (d) 200

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Figure 11

Centerline velocity development for the 500 μm channel at Re of (a) 0.5, (b) 5, (c) 50, and (d) 200

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Figure 12

Entrance length comparison between present data and conventional correlations

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Figure 13

Proposed entrance length correlation for square microchannels below 500 μm with present experimental data of the 100 μm and 200 μm channels and the error in the fit

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Figure 14

Proposed entrance length correlation for square channels at the microscales and macroscales and the error in the fit

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Figure 15

Proposed general entrance length correlation for microchannels, independent of cross-sectional aspect ratio, and the error in the fit

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