Numerical and experimental investigations of chaotic mixing behavior in an oscillating feedback micromixer

- A 2-D high-efficiency micromixer was designed using the Coanda effect.
- Transverse flow perturbation was generated through the feedback channel.
- Time-periodic chaotic mixing behavior was investigated.
- Lagrangian particle tracking was employed to characterize chaotic advection.

An oscillating feedback micromixer comprising an inlet channel, two Coanda steps, a divergent chamber, a splitter, two feedback channels, and an outlet channel was designed considering the Coanda effect. Two-dimensional unsteady simulations were employed to study the impact of the Reynolds number on the oscillation frequency, pressure drop, and chaotic mixing. The switching mechanism of the fluidic oscillation based on the Coanda effect was examined in detail. Three Lagrangian particle tracking indicators, the Poincaré maps, particle dispersion distribution, and stretching of fluid filaments, were employed to observe and quantify the mixing induced by chaotic advection. The Lagrangian simulation results showed that the average stretching index increased from 4.91 to 5.57 with Reynolds number (Re) increased from 33.3 to 100. In addition, the mixing efficiency was quantified using a mixing index based on the standard deviation of the scalar species distribution. The results indicated that the mixing efficiency increased with the increase of Reynolds number, and the mixing efficiency of 75.3% could be achieved at Re = 100. The mixing of colorless and blue deionized water was tested experimentally to verify the simulated concentration fields, and the experimental results were in good agreement with the simulation results.

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