A Numerical Study on Liquid Mixing in Multichannel Micromixers Yuanhai Su, †,‡ Anna Lautenschleger, † Guangwen Chen, ‡ and Eugeny Y. Kenig* ,† † Chair of Fluid Process Engineering, Faculty of Mechanical Engineering, University of Paderborn, D-33098, Paderborn, Germany ‡ Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China ABSTRACT: Single microchannels and their arrangements for liquid mixing are investigated numerically. A smaller lateral inlet diameter and the zigzag form of the channels are found to be beneficial for the mixing performance in microchannels. Under proper operational conditions, the mixing process can be almost completed. Furthermore, some constructal distributor designs for the arrangement of microchannels are proposed and analyzed with regard to the fluid distribution. For the optimized distributor, the standard deviation from perfectly even distribution does not exceed 4% while keeping the pressure drop low. Two multichannel micromixer designs are suggested, with accordingly optimized microchannels and distributors, and their mixing performance is very close to that of a single microchannel. The specific energy dissipation in the multichannel micromixer is in the range of 0.016-93 W/kg, which is similar to batch reactors. Finally, the design procedure for multichannel micromixers is proposed. 1. INTRODUCTION Mixing processes in liquid-liquid systems are widespread in the process industry. They comprise macro- and mesomixing (coarse-scale phenomena), and micromixing that occurs on molecular scale. In many unit operations, for example, precipitation, 1 crystallization, 2,3 polymerization, 4 self-catalysis, 5 and enzymatic catalysis, 6 the mixing efficiency represents a decisive factor, whereas an optimized mixing performance improves the contact of reactants and greatly influences selectivity, yield, and quality of products. In particular, the mixing performance may control the molecular weight distribution in polymerization. Recent progress in reactor design yielding better mixing efficiency has been remarkable. Impinging flow reactors, 7 rotating packed bed reactors, 8,9 static mixers with internal baffles, 10 and micromixers 11 demonstrate outstanding progress in reactor design. During the last two decades, chemical engineering has experienced a spectacular trend toward microscale applications. This represents one of the most important areas in the process intensification concept. The microscale applications benefit from the miniaturization of the unit-building channels in which the characteristic lengths reach the values typical for boundary layers. 12-14 A number of micromixers and microreactors have been designed, attracting increasing attention of both industry and academia. 15-21 Furthermore, a considerable variety of novel micromixer concepts have been proposed, such as interdigital micromixer, 22 split-and-recombine micromixer, 23 micromixer based on the collision of microsegments, 24 multifunctional micromixer, which makes use of alternating current electroosmotic flow and asymmetric electric field, 25 packed-bed microreactors, 18,26,27 etc. However, because of their complex structures, manufacturing of these micromixers is difficult, and their practical application is limited. In contrast, T-shaped microchannel mixers are easy to design and manufacture; hence they are widely used for laboratory tasks and have high potential for industrial application. Many research groups investigated hydrodynamics and mixing in microchannels by numerical and experimental methods. Engler et al. 28 had revealed that there were three different laminar flow regimes inside the junction of a T-shaped microchannel, depending on the Reynolds number, stratified flow, vortex flow, and engulfment flow. It was found that the vortices inside a T-shaped microchannel with a rectangular cross-section occurred even at low Reynolds numbers and they were beneficial to the mixing performance improvement. Adeosun and Lawal 29 used residence time distribution (RTD) to characterize the flow and mixing in a T-shaped microchannel by computational fluid dynamics (CFD) simulations and UV-vis absorption spectroscopy detection technique for experimental validation. Their numerical and experimental results were in good agreement, demonstrating that CFD simulations could be used as a predictive tool in the design and optimization of microchannels. It is well-known that the geometrical structures of reactors and mixers affect the hydrodynamics and, consequently, the mixing performance. Hong et al. 30 carried out a numerical analysis of mixing in an innovative microchannel with modified Tesla structures over a wide range of flow rates. It was found that these structures were advantageous for mixing at higher flow rates, and the mixing performance was influenced by both diffusion and chaotic advection caused by the Tesla structures. Chang and Cho 31 designed and fabricated a microchannel with alternating whirls and laminations. This design was found to be capable of establishing repeated rotational flow fields that could mix fluids in a wide range of flow rates. Mengeaud et al. 32 numerically studied the mixing process in a zigzag micro- channel with a “Y” inlet junction. They demonstrated the effects of both flow rate and channel geometry on hydro- dynamics and mixing efficiency. Below the critical Reynolds number, the effect of the zigzag configuration on hydro- dynamics was found to be negligible, and mixing was entirely dominated by molecular diffusion, while the diffusion distance Received: June 18, 2013 Revised: November 22, 2013 Accepted: December 2, 2013 Published: December 2, 2013 Article pubs.acs.org/IECR © 2013 American Chemical Society 390 dx.doi.org/10.1021/ie401924x | Ind. Eng. Chem. Res. 2014, 53, 390-401