Characterization of the Mixing Quality in Micromixers

Abstract

The laminar flow patterns and mixing performance of two different micromixers have been investigated and quantified using CFD. The micromixer geometries consist of a channel with either diagonal or asymmetric herringbone grooves on the channel floor. The numerical results show that a single helical flow is produced for the diagonal mixer, whereas the herringbone mixer creates a double helical flow, composed of an alternating large and small vortex. Particle tracking of a tracer shows that very little convective mixing occurs in the diagonal mixer. However, in the herringbone mixer, very good mixing occurs. Quantitative analysis methods that are traditionally used for characterizing macro-scale static mixers have been employed. Calculation of the variance of tracer dispersion and the stretching has shown to be well adapted for quantifying the mixing in the micromixers. However, methods based on the deformation rate appear to be less suitable. The results are in excellent agreement with previous experimental findings.

Evaluation of Floor-grooved Micromixers using Concentration-channel Length Profiles

“…Furthermore, it is evident that at the same groove depth, a much smaller L m value is needed for the SHM than the SGM, confirming that mixing within the SHM is more effective and faster than that within the SGM. This is consistent with reported simulation and experimental results [11,12]. …”

“…Stroock et al [11] studied the mixing in both staggered herringbone micromixers (SHM) and slanted groove micromixers (SGM) at low Re and showed that mixing could be enhanced by using herringbone shaped asymmetric structures on the floor of the channel. Two counter-rotating vortices were found in the channels of SHM in a study by Aubin et al [12], in which a computational fluid dynamics (CFD) was also used for simulation. Kim et al [13] presented a chaotic micromixer, in which chaotic mixing was achieved by periodic perturbation of a helical type of flow obtained by slanted grooves.…”

“…To characterize the mixing performance of the micromixers in order to better understand and design more efficient micromixers for different applications, a number of techniques, both experimentally [14][15][16][17][18] and theoretically [12,[19][20][21][22][23][24][25][26][27][28], have been employed. Particularly, CFD has been widely used to study the mixing behavior of micromixers in details.…”

“…These observations strongly indicate that the initial chaotic mixing in SHM is only limited to the regions close to the grooves until the upper portion of the channel fluid is sufficiently affected by the two opposing vortices. Since the two mixing fluids are first turned clockwise and then counter-clockwise by two vortices, the interface of two fluids (not the interface of two vortices) remains in the middle of the channel [12]. As the concentrations at the middle of the channel cross-section are always controlled by the large vortex, either left-positioned (high concentration) or right-positioned (low concentration), the concentration profiles at the middle of the channel cross-section, showed substantial oscillations at all times until mixing completed, as shown in Figure 3(d).…”

Effect of Optical Rotor on Mixing in Y-shaped Microchannel Flow

“…Another greatly efficient passive mixer is the one that uses chaos due to the complexity of the conduct channels such as: herringbone groove channel (5), (6) , or C-shaped serpentine channel developed by Liu et al (7) . Passive mixers have advantage in term of easily installing into an integrated device.…”