Modeling and simulation of a split and recombination-based passive micromixer with vortex-generating mixing units

Abstract

As a state-of-the-art technology, micromixers are being used in various chemical and biological processes, including polymerization, extraction, crystallization, organic synthesis, biological screening, drug development, drug delivery, etc. The ability of a micromixer to perform efficient mixing while consuming little power is one of its basic needs. In this paper, a passive micromixer having vortex-generating mixing units is proposed which shows effective mixing with a small pressure drop. The micromixer works on the split and recombination (SAR) flow principle. In this study, four micromixers are designed with different arrangements of mixing units, and the effect of the placement of connecting channels is evaluated in terms of mixing index, pressure drop, and mixing performance. The channel width of 200 μm, height of 300 μm, and size of mixing units are maintained constant for all the micromixers throughout the evaluation process. The numerical simulation is performed for the Reynolds number (Re) range of 0.1-100 using Comsol Multiphysics software. By categorizing the flow patterns into three regimes based on the range of Re, the fluid flow throughout the length of the micromixer is visualized. The micromixer with dislocated connecting channels provides a satisfactory result with the mixing index of 0.96 and 0.94, and the pressure drop of 2.5 Pa and 7.8 kPa at Re = 0.1 and Re = 100 respectively. It also outperformed the other models in terms of the mixing performance. The proposed micromixer might very well be used in microfluidic devices for a variety of analytical procedures due to its straightforward construction and outstanding performance.

Keywords: Flow visualization; Fluid mixing; Mixing index; Numerical simulation; Passive micromixer.

Fig. 1

3D view of four micromixer models: (a) Model-1, (b) Model-2, (c) Model-3, and (d) Model-4.

Fig. 2

Schematic diagram of four micromixer models with geometrical parameters: (a) Model-1, (b) Model-2, (c) Model-3, and (d) Model-4.

Fig. 3

(a) Model geometry of Ansary et al. [22], (b) comparison of mixing index at cross-sectional plane for model validation test.

Fig. 4

Flow of two fluid streams through Model-3 micromixer.

Fig. 5

xy-plane representation of flow visualization of all micromixer models at the last two units and the exit according to three regimes: (a) at the lamination regime, (b) at the transitional regime, and (c) at the chaotic regime.

Fig. 6

yz-plane representation of concentration profile showing the effect of Re at: (a) entrance section and (b) exit section.

Fig. 7

The concentration profiles of the micromixers at three flow regimes in xy-plane: (a) Model-1, (b) Model-2, (c) Model-3, and (d) Model-4.

Fig. 8

(a) Mixing index and (b) pressure drop plots of four micromixer models with respect to Re.

Fig. 9

Mixing Index growth along the axial length, X (μm), of Model-3 at different Re values.