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Research Papers: Fundamental Issues and Canonical Flows

Experimental and Numerical Evaluation of a Scaled-Up Micromixer With Groove Enhanced Division Elements

[+] Author and Article Information
Ibrahim Hassan

e-mail: ibrahimh@alcor.concordia
Department of Mechanical and
Industrial Engineering,
Concordia University,
Montreal, QC, H3G 2W1, Canada

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received February 1, 2012; final manuscript received August 2, 2012; published online December 21, 2012. Assoc. Editor: Kendra Sharp.

J. Fluids Eng 135(1), 011201 (Dec 21, 2012) (14 pages) Paper No: FE-12-1051; doi: 10.1115/1.4023073 History: Received February 01, 2012; Revised August 02, 2012

A novel passive enlarged micromixer has been proposed and experimentally and numerically investigated in this study over 0.5 ≤ Re ≤ 100. Flow visualization was applied to qualitatively assess flow patterns and mixing, while induced fluorescence was applied to quantify the distribution of species at six locations along the channel length. Numerical simulations were applied to assist in the description of the highly rotational flow patterns. Two individual species are supplied through a total of three lamellae, which are converged prior to entering the main mixing channel, which consists of five groove-enhanced circular division elements. Grooves along the bottom surface of the channel allow for the development of helical flow in each subchannel of the mixing element, while the circular geometry of the mixing elements promotes the formation of Dean vortices at higher Reynolds numbers. The main mixing channel is 2000 μm wide and 750 μm deep, while the total channel length is 137.5 mm. Flow rotation was observed at all investigated Reynolds numbers, though the degree of rotation increased with increasing Re. A decreasing-increasing trend in the degree of mixing was observed, with a critical value at Re = 10. Of the investigated cases, the highest degree of mixing at the outlet was achieved at Re = 0.5, where mass diffusion dominates. A standard deviation of σexp = 0.062 was reported. At Re = 100, where advection dominates and secondary flow develops, a standard deviation of σexp = 0.103 was reported, and the formation of additional lamellae was observed along the channel length due to the merging of rotated substreams. The additional lamellae contributed to the increase in interfacial area and reduction of the path of diffusion.

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Figures

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Fig. 2

Critical dimensions of test section and sealing slot schematic

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Fig. 1

Three dimensional view of test section indicating locations of measurement. For the experiment, grooves are located at the bottom surface.

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Fig. 3

Facilities used for flow visualization and induced fluorescence experiments

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Fig. 9

Slight asymmetry noted in manufactured device

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Fig. 10

Comparison of E1 at Re = 100. (a) Flow visualization image (b) concentration distribution along center of channel (c) section view of mixing element.

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Fig. 11

Flow visualization over 0.5 ≤ Re ≤ 100 shown at inlet, mixing elements 1, 3 and 5 and outlet

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Fig. 4

Sample calibration curve showing the linear relationship between fluorescence intensity and concentration

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Fig. 5

Data processing procedure. (a) Raw gray scale image (b) concentration map obtained via calibration curve (c) concentration distribution along line of measurement.

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Fig. 6

Grid system shown for half of a mixing element

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Fig. 7

Grid independence performed at outlet of first mixing element (a) concentration distribution and (b) velocity distribution

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Fig. 8

Numerically and experimentally (IF) obtained concentration distribution at Re = 0.5 and 50 at the inlet (S1) and exit (S2) of the first mixing element

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Fig. 12

Induced fluorescence concentration maps at select Reynolds numbers and locations

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Fig. 13

Concentration isosurface at (a) Re = 0.5 (K = 0.15) and (b) Re = 100 (K = 30.15)

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Fig. 14

(a) Numerically obtained concentration distribution over cross section and (b) IF concentration distribution. Re = 50, S3.

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Fig. 15

Outlet concentration distribution over 0.5 ≤ Re ≤ 100. Top images show cross section (numerical). Bottom images show concentration distribution obtained via induced fluorescence.

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Fig. 16

Standard deviation at S6 (outlet) for 0.5 ≤ Re ≤ 100

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Fig. 17

Scaling of arbitrary mixers for comparison. The equivalent distance is represented by x* = 1.

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Fig. 18

Comparison of the present device with the crosswise ridge and staggered Dean vortex micromixers [17,27]

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Fig. 19

Comparison of mixers at various equivalent lengths

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