Experiments in Fluids

, Volume 49, Issue 3, pp 733–747

Experimental and numerical investigation of a scaled-up passive micromixer using fluorescence technique

Research Article

Abstract

The present paper investigates experimentally and numerically a scaled-up micromixer that combines the mixing principles of focusing/diverging and flow split-and-recombine. The micromixer consists of two units called “cross” and “omega”, which are similar to a zigzag structure. The total length is 199.5 mm with a depth of 3 mm. Fluorescence technique is used in the present study for local quantitative measurements of concentration. Two syringe pumps are used to supply the working fluids at two inlets. The testing range of Reynolds number is at 1 ≤ Re ≤ 50. The results of the experiment, obtained by fluorescence technique, are supported by the mixing visualization. The experimental results show that the mixing efficiency decreases at Re ≤ 10 and increases at Re ≥ 10. This is caused by the change in mixing mechanism from mass-diffusion domination to mass-convection domination. After five cells, the mixing efficiency reaches to 70% at Re = 50. The computational fluid dynamics is applied to assist in the understanding of fluid characteristics in channels. The simulation has a good agreement with the experiment. Based on the simulation results, vortices are observed in the channels at high Re, which could stretch and fold the fluids to enhance the effect of mass-convection on mixing. This design has the potential to be developed for micromixers with high flow rates.

List of symbols

A

Interface area (m2)

B

Ratio between intensity and concentration

C

Concentration (μg/l)

Ci

Concentration at ith position (μg/l)

\( \bar{C} \)

Average concentration (μg/l)

C(x, y)

Local dye concentration (μg/l)

Cref

Reference concentration (μg/l)

\( C^{\prime}_{x} \)

Concentration gradient in x-direction (μg/l·m)

D

Diffusion coefficient (m2/s)

DH

Hydraulic diameter (m)

H

Height of channel (mm)

If

Local fluorescence intensity

Iref

Reference fluorescence intensity

L

Length of test-section (mm)

Lt

Diffusion path (m)

M

Mixing efficiency

\( \dot{m} \)

Mass flow rate (kg/s)

N

Total number of sampling

P

Pressure (Pa)

td

Diffusion time (s)

U

Average velocity (m/s)

V

Velocity vector (m/s)

W

Width of channel (mm)

Acronyms

\( \text{Re} \)

Reynolds number

\( {\text{Pe}} \)

Péclet number

Greeks

μ

Viscosity of working fluids (N·s/m2)

ρ

Density of working fluid (kg/m3)

Subscript

m

Micro-scale mixer

s

Scaled-up mixer

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Department of Mechanical and Industrial EngineeringConcordia UniversityMontrealCanada

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