Research Papers: Flows in Complex Systems

Mixing Evaluation of a Passive Scaled-Up Serpentine Micromixer With Slanted Grooves

[+] Author and Article Information
Ibrahim Hassan

e-mail: ibrahimh@alcor.concordia.ca
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 April 8, 2012; final manuscript received April 3, 2013; published online June 3, 2013. Assoc. Editor: Michael G. Olsen.

J. Fluids Eng 135(8), 081102 (Jun 03, 2013) (12 pages) Paper No: FE-12-1180; doi: 10.1115/1.4024146 History: Received April 08, 2012; Revised April 03, 2013

A novel, passive, scaled-up micromixer based on fluid rotation is proposed and evaluated experimentally and numerically over Reynolds numbers ranging from 0.5 to 100. Flow visualization is employed to qualitatively assess flow patterns, while induced fluorescence is used to quantify species distribution at five locations along the channel length. Two individual fluids are supplied to the test section via a Y-inlet. The fluid enters a meandering channel with four semicircular portions, each of which is lined with nine slanted grooves at the bottom surface. The main mixing channel is 3 mm wide and 0.75 mm deep, with a total length of 155.8 mm. Numerical simulations confirm rotation at all investigated Reynolds numbers, and the strength of rotation increases with increasing Reynolds number. Grooves are employed to promote helical flow, while the serpentine channel structure results in the formation of Dean vortices at Re ≥ 50 (Dean number ≥ 18.25), where momentum has a more significant effect. A decreasing-increasing trend in the degree of mixing was noted, with an inflection point at Re = 5, marking the transition from diffusion dominance to advection dominance. The increase in interfacial surface area is credited with the improved mixing in the advection-dominant regime, while high residence time allowed for significant mass diffusion in the diffusion-dominant regime. Good mixing was achieved at both high and low Reynolds numbers, with a maximum mixing index of 0.90 at Re = 100.

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Fig. 1

Test section depicting locations of measurement

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Fig. 2

Dimensions of test section

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Fig. 3

Experimental facility used for flow visualization and induced fluorescence experiments

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Fig. 4

Sample calibration curve depicting linear relationship between fluorescence concentration and intensity

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Fig. 5

Data processing procedure

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Fig. 6

Boundary conditions and grid system used for numerical simulation

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Fig. 7

Grid independence performed at exit of first mixing element (L2). Re = 100.

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Fig. 8

Qualitative validation of numerical work at Re = 50

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Fig. 9

Quantitative validation of numerical work at Re = 1 and 50

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Fig. 10

Flow visualization of entire test section at various Reynolds numbers

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Fig. 11

Close up of grooves 2–8 in the first mixing element at Re = 100

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Fig. 12

Channel cross-section concentration distribution and streamlines at C1 and C2 over 0.5 ≤ Re ≤ 100 (numerical results)

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Fig. 13

Concentration distribution at Re = 10 at L2

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Fig. 14

Concentration distribution at Re = 50 at L2

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Fig. 15

Numerically obtained evolution of mixing index along channel length for 0.5 ≤ Re ≤ 100

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Fig. 16

Numerically and experimentally obtained mixing indices at the outlet

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Fig. 17

Mixing indices of various mixers at similar equivalent lengths



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