# Numerical and Experimental Investigations of a Micromixer with Chicane Mixing Geometry
## 1 Introduction
As a result, the lamellas become thinner, the diffusion length decreases and therefore, the flows mix more quickly. This effect is called secondary flows, which [PERSON] [13; 14] explored for the first time. He included the significant change of the velocity field in curved pipes and the resulting formation of vortices, and the flow remained laminar. Nowadays, the utilization of this phenomenon is called \"vortex flow\", which finds its application in curved microchannels, such as in T-form mixers [7; 15; 16], Y-form mixers [16], spiral microchannels [17], herringbone [18], chicane or serpentine [19], with embedded obstructions [20], etc. The most important feature of these microreactors is an effect of the volume flow rate on intensity of vortex structures appearing [21] and on the chemical performance [22]. While the vortex flow is characterized by the symmetry of both mixed flows, the engulfment flow has no symmetry [12]. Broken symmetry results in the flow reaching the opposite side of the mixing channel. This significantly reduces the diffusion length and further intensifies the mixing process. In comparison to diffusion micromixers, convective micromixers utilizing vortex and engulfment flow regimes provide faster mixing but also have several disadvantages, such as higher values in the decrease of pressure. To solve this, the supply pumps with higher power and higher energy consumptions are to be operated. In addition, the tubing should be more robust in order to withstand higher pressure. In turn, this increases setup and operating costs. The investigation of flow regimes such as stratified, vortex, and engulfment flows is challenging because every type of micromixer is unique in its geometrical structure and therefore has its own range of the flow regimes and vortex patterns. Several researches investigated the mixing process in a micromixer with meander structures similar to that being investigated in the present study. [PERSON] and co-authors [19] have investigated a micromixer with 100 \(\upmu\)m-wide zig-zag channel. Zigzag elements have a positive effect on mixing in comparison with a straight channel. Moreover, mixing efficiency greatly increases for Reynolds numbers Re > 80, which was explained by the flow recirculation phenomenon. [PERSON] and [PERSON] [23] have studied in their article a sinusoidal wave form micromixer with different phase shifts. The shift at 3/4 \(\pi\) shows the best mixing index, while shifts at 0 (pure sinusoidal form) and pi (symmetrical form) have a much smaller mixing index, as well higher critical Reynolds. [PERSON] et al. [21] investigated and compared a Y-junction and an \"S-form\" micromixer using a computational fluid dynamics (CFD) simulation. The results showed the higher mixing efficiency of the \"S-form\" mixer in comparison to the Y-mixer only by vortex flow regime. In the case of stratified flow, only the hydraulic diameter plays a role and there is no difference between the Y-mixer and the \"S-form\" mixer in hydraulic diameter \(\mathrm{dh}=1\) mm. [PERSON] et al. [24] experimentally investigated the mixing process of \"S-form\" micromixers using two different indicative reactions: consecutive Diazo Coupling and parallel neutralization and hydrolysis reactions. They showed that the high mixing index can only be achieved using a vortex flow and there is likely a correlation between mixing index and pressure drop. It was also experimentally found, that the volume flow rate plays a significant role in the mixing process in this type of micromixers. There are zones with almost zero mixing efficiency, stagnation zones and many areas, where previously mixed flows mix again. [PERSON] et al. [25] studied a neutralization reaction in a similar tangential micromixer--FlowPlate(tm) 102 and 260, produced by Lonza. The results indicated that at comparable Reynolds numbers the S-shaped channel allows faster mixing in comparison with the SZ-shaped and caterpillar channels. A micromixer with a similar structure was investigated by [PERSON] et al. [26].