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Item type:Publication, Access status: without files , Experimental and numerical investigation of competitive chemical reactions on different scales in milli reactorsPublicationtype: Doctoral Thesis13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Local analysis of micro mixing for the Villermaux-Dushman protocol by using the imaging UV-Vis spectroscopyThe Villermaux-Dushman protocol with UV-Vis analytics is an established tool to characterize the global micro mixing performance in process equipment. The local mixing process is described by a micro mixing model (incorporation model), originally designed for turbulent flows. The novel imaging UV-Vis spectroscopy used in this work uncovers locally resolved micro mixing phenomena in a laminar split-and-recombine (SAR) mixer unit manufactured from selective laser-induced etching (SLE). The local absorbance is recorded with a high spatial resolution camera through a telecentric lens and post-processed into local concentration fields of components. The method unveils discrepancies of the micro mixing time determined from the conventional incorporation model in laminar flow and the locally recorded mixing process. The micro mixing time rather needs to be seen as a mean micro mixing time instead. Furthermore, the spatial information obtained by the imaging UV-Vis spectroscopy gives insight into local micro mixing and selectivity, yielding new approaches to equipment optimization.Publicationtype: Journal Article54 413 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , CFD-based compartment modeling of continuous polymer reactors in milli-structured apparatuses by use of the mean age theory(2023-07-13); ; ; ; The transformation of energy-intensive batch processes for small-scale polymer specialties into more energy-efficient continuous processes is a challenging task due to the occurrence fouling. To determine safe operating windows, a proper reactor model is needed. Indeed, a computational fluid dynamics (CFD) can resolve potential fouling zones; however, the computational demand of a detailed CFD of entire reactors is in general uneconomical for parameter studies, transient problems, or complex reaction mechanisms such as polymerizations. Contrary, reduced basic reactor models, such as plug flow reactors, can be used for simulation studies of entire reactors due to their low computational demand but cannot resolve potential fouling zones. The compartment modeling approach offers a promising method to combine relevant fluid dynamics from CFD models with the simulation of complex reaction mechanisms. In this contribution, a compartment model of a 3 m milli-structured reactor for polymer synthesis is derived from a reduced CFD model. The computational CFD mesh of a section of the reactor is transformed into a cascade of continuously stirred tank reactors (CSTRs) by clustering the CFD cells based on the local mean age, allowing the spatial interpretation of fouling zones. The mean age theory is used to evaluate the fluid dynamics and mixing characteristics of the derived compartment model and compare it with the CFD. With a scale-up, the compartment model describes the entire residence time reactor and enables transient simulations and parameter studies with a significantly decreased computational demand. The compartment model is validated with experimental data for a catalytic polymerization process.Publicationtype: Journal Article19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A novel approach for visualizing mixing phenomena of reactive liquid-liquid flows in milli- and micro-channels(Frontiers Media S.A., 2022-06-06); ; ; ; Modular milli- and micro-structured systems represent a promising approach to exploit the potential of micro-process technology, including precise reaction control and scale-up. A major drawback of micro-structured devices is fouling and mixing mechanisms need to be investigated phenomenologically to better understand the processes that lead to fouling. Previous work was conducted to resolve 3D concentration fields by means of Laser-Induced Fluorescence (LIF) using a Confocal Laser Scanning Microscope (CLSM) (Frey et al., J Flow Chem, 2021, 11, 599–609). While the CLSM-LIF method yields detailed insight into concentration fields down to a few micrometers, it is limited to stationary flow structures only. Aubin et al. (Chemical Engineering Science, 2010, 65, 2065–2093) give a comprehensive review of methods to analyze mixing behavior. Most recent optical measurement methods rely on the detection of a single compound in mixtures. In case of reactive mixing, Tthe state of the art procedures to locally visualize micro mixing relies on tracking a reaction product which forms on molecular scale. In literature, only small micro-structures are manufactured from transparent materials, however larger milli-structures often lack optical accesses with sufficient quality. Selective laser-induced etching (SLE) is a new technique which enables the fabrication of larger milli-structures in transparent materials that are relevant for industry-scale applications. This work develops a method based on a concept of Kexel et al. (Chemie Ingenieur Technik, 2021, 93, 830–837) visualizing the selectivity of a competitive-consecutive gas-liquid reaction in a Taylor bubble flow. The main goal of this work is the analysis of the absorbance spectra of bromothymol blue (BTB) at different pH values in a miscible liquid-liquid system in a fused silica split-and-recombine mixer. The milli-structure of the mixer is manufactured by means of SLE. Backlight at different wavelengths is pulsed matching the recording frequency. In contrast to conventional UV/Vis setups, the absorbance is recorded locally within the mixer. The proposed method yields the 2D concentration distribution of multiple species with high spatial resolution. The spatially resolved reactant and product distribution unveils micro mixing and can yield important information about local root causes of fouling.Publicationtype: Journal ArticleScopus© Citations 1 149 528 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , CFD analysis of asymmetric mixing at different inlet configurations of a split-and-recombine micro mixer(Springer, 2021-07-01); ; ; ; 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.Publicationtype: Journal ArticleScopus© Citations 2 150 153