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New article on the simulation of split-and-recombine micromixers published in Journal of Flow Chemistry

One of the biggest challenges in continuous polymer synthesis is fouling. This is being investigated in more detail as part of the ENPRO 2 framework programme funded by the Federal Ministry of Education. An essential step to avoid fouling is the pre-mixing of the reaction components. At the Institute for Multiphase Flows, mixing is therefore investigated in detail both experimentally and simulatively in micromixers. The latest results can be found in the Institute's most recent publication.

Abstract: In the scope of the ENPRO II initiative (Energy Efficiency and Process Intensification for the Chemical Industry), a major challenge of process intensification of polymer synthesis in continuous systems is fouling. Pre-mixing is a key aspect to prevent fouling and is achieved through milli and micro structured devices (Bayer et al. 1). While equal volume flow ratios are well investigated in milli and micro systems, asymmetric mixing tasks have received less attention. This paper investigates the dependency of mixing phenomena on different flow rate ratios and modified inlet geometries. A split-and-recombine (SAR) mixer is modified by means of an injection capillary to facilitate the asymmetric mixing task. Asymmetric volume flows of ratios between 1:15 and 1:60 are investigated; the velocity ratios range from 0.5 to 2. The setup is simulated with the Computational Fluid Dynamics (CFD) tool ANSYS®; Fluent. The species equation is solved directly without the use of micro mixing models. The simulation is validated by means of a concentration field in a mixing Tee using Laser-Induced Fluorescence (LIF) with a Confocal Laser Scanning Microscope (CLSM). The three dimensional flow structures and the mixing quality are analyzed as a measure for micro mixing. The calculated concentration fields show good agreement with the experimental results and reveal the secondary flow structures and chaotic advection within the channel. The injection of the small feed stream is found to be very efficient when drawn into the secondary structures, increasing the potential of diffusive mixing. CFD simulations help to understand and locate such structures and improve the mixing performance.

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