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Item type:Publication, Access status: with files , Lagrangian μ-particle tracking velocimetry analysis of microscale flow over structured surfaces(American Chemical Society (ACS), 2026-10-08); ; ; ; This work aims to provide an experimental basis for the improvement of (bio)reactors by studying flow over micro- and nanostructured surfaces, with a focus on microscale mass transport toward and away from the surface. μ-Particle tracking velocimetry is employed in a microreactor to experimentally obtain Lagrangian trajectories of flow-following tracer particles. The method also resolves three-dimensional, time-dependent velocity fields. The derived mean velocity profiles agree well with the theory of flow over porous walls. Beyond averaged Eulerian velocities, the Lagrangian framework captures near-surface interactions. The Lagrangian analysis of different surfaces indicates that rectangular structured microgrooves increase the wall contact of the tracer particles, especially when the flow is oriented perpendicular to the microgrooves. Particularly, this approach enables resolution of trapping phenomena and localized recirculation dynamics. Nanostructuring by growing a carbon nanotube forest increases surface area and modifies local fluid dynamics, thereby enhancing contact with (bio)catalysts that are potentially functionalized on the nanotubes in future applications.Publicationtype: Journal Article41 15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Impact of permeability of triply periodic minimal surface-based substrates on multiwalled carbon nanotube growth(American Chemical Society (ACS), 2026-08-05); ; ; ; Lumpp, DominiqueDue to their excellent thermal and electrical properties combined with pronounced porosity, carbon nanotube forests are promising as catalyst support materials for smart reactors. To maximize catalytic turnover, it is essential to increase the available surface while maintaining precise control over reactant flow and heat distribution. In this work, multiwalled carbon nanotubes are grown on three-dimensional substrates based on triply periodic minimal surfaces, which offer superior mechanical properties alongside controlled flow dynamics and enhanced heat transfer rates. The substrates are fabricated via laser powder bed fusion and subsequently coated using injection chemical vapor deposition. To evaluate the design limitations of the three-dimensional substrates for CNT growth, the impact of a decreasing permeability on the coating’s morphology is investigated. As the permeability decreases with the unit cell size of the triply periodic minimal surfaces and the introduction of an external wall, the characteristic CNT forest structure gradually transforms. Provided that permeability and precursor accessibility to the internal surfaces remain sufficiently high, the morphology and composition of CNT forests closely resemble those grown on flat substrates. Introducing the wall leads to a transition from vertically aligned CNT forests to horizontally oriented CNT networks due to enhanced laminar-like flow characteristics. While less dense, it offers an increased CNT quality. Below a critical minimal permeability, carbon nanostructures with numerous defects form. The successful coating and control of its morphology enable the utilization of the CNT for further smart tailoring of the reactor.Publicationtype: Journal Article87 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Comprehensive study of 3D liquid flow fields in additively manufactured structures for SMART reactors using large-scale vertical magnetic resonance imaging and computational fluid dynamics(Elsevier, 2026-04-24); ; ; ; Triply Periodic Minimal Surface (TPMS) structures have emerged as a new class of porous materials with variable geometries and favourable transport properties, making them promising for reactor internals in chemical engineering. However, experimental data on internal TPMS flow behaviour are still limited. To address this gap, the flow behaviour in additively manufactured TPMS structures is analysed using three-dimensional Magnetic Resonance Imaging (MRI) velocimetry in a large-bore vertical 3 T MRI system, in cylindrical columns of 38 mm diameter and Reynolds numbers between 50 and 300. Three different TPMS geometries are investigated, and consistency between Computational Fluid Dynamics (CFD) simulations and experimentally measured MRI velocity fields is established through cross-validation. The MRI system provides fully three-dimensional velocity fields with a divergence deviation below 6 %. MRI revealed distinct flow features: the Gyroid TPnS exhibited pronounced channelling, while the Schwarz-Diamond TPSf showed merge-split behaviour, achieving a 46 % increase in lateral mixing compared to the Gyroid TPnS structures. Numerical simulations reproduce the flow features and show agreement with the MRI data. The combined methodology demonstrates the suitability of MRI velocimetry for the experimental validation of CFD simulations and establishes a robust foundation for future studies of heat and mass transfer, as well as reactive flow, in structured reactor systems.Publicationtype: Journal Article70 85 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Design guidelines for laser powder bed fusion of triply periodic minimal surface structures for applications in smart reactors(Springer, 2026-01-20); ; ; ; Additive Manufacturing (AM), particularly Laser Powder Bed Fusion (PBF-LB/M), has transformed the production of complex metallic structures, enabling applications in smart reactors where enhanced heat and mass transfer at minimal pressure drop are critical. Triply Periodic Minimal Surface (TPMS) structures, such as Gyroid-TPSf and Schwarz-Diamond-TPSf geometries, offer unique advantages due to their high surface area-to-volume ratios, tunable porosity, and zero mean curvature. However, their manufacturability using PBF-LB/M remains underexplored, especially for demanding applications in process engineering that require structural integrity under extreme conditions. This study investigates the design and manufacturability of TPMS structures using 316L stainless steel via PBF-LB/M, focusing on the interaction of the key parameters porosity, unit cell size, and sheet thickness, of which two are independent variables while the third is a dependent variable. Through numerical simulations, experimental validation, and process optimization, practical design guidelines are developed. In this study, the design parameters of Gyroid-TPSf and Schwarz-Diamond-TPSf samples include porosities ranging from 70 to 90% and unit cell sizes from 2 to 20 mm. The results indicate that specifically, at large unit cell sizes (e.g., 20 mm), the decreased curvature radius reduces self-supporting effects, leading to insufficient mechanical stability during printing and resulting in local deformation. Conversely, at small unit cell sizes combined with high porosity levels (e.g., 2 mm and 90%), the sheet thickness becomes critically thin, often below the printable resolution, resulting in incomplete or fragile structures. CFD simulations were validated against experimental data across various volume flow rates. This work enables a knowledge-based selection of a suitable type of TPMS and its design parameters depending on the required flow characteristics in a given process engineering task while maintaining manufacturability. In conclusion, the study underscores the need for further refinement of design and manufacturing processes to fully exploit their benefits.Publicationtype: Journal Article95 101 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Wireless and passive pressure detection using magneto-mechanical resonances in process engineering(IOP Publishing, 2025-08-31); ; ; ; A custom-developed magneto-mechanical resonator (MMR) for wireless pressure measurement is investigated for potential applications in process engineering. The MMR sensor utilises changes in the resonance frequency caused by pressure on a flexible 3D printed membrane. The thickness of the printed membrane plays a crucial role in determining the performance and sensitivity of MMRs and can be tailored to meet the requirements of specific applications. The study includes static and dynamic measurements to determine the pressure sensitivity and temporal resolution of the sensor. The results show a minimum sensitivity of 0.06 Hz mbar − 1 and are in agreement with theoretical calculations and measurements. The maximum sensor readout frequency is 2 Hz in this study. Additionally, the temperature dependence of the sensor is investigated, revealing a significant dependence of the resonance frequency on temperature. The developed MMR offers a promising and versatile method for precise pressure measurements in process engineering environments.Publicationtype: Journal Article72 69 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Advancing multiphase flow imaging with high-density receiver arrays: MRI velocity measurements in structured packing with Schwarz-Diamond-TPSf designEffective mixing is fundamental to optimizing process performance in the chemical and biochemical industries. The mixing efficiency is predominantly governed by the fluid flow within these systems [1]. Understanding such mixing processes significantly benefits from precise velocity measurements and high-resolution imaging techniques. Nonetheless, obtaining detailed three-dimensional insights into their mixing states continues to present a substantial challenge. Magnetic Resonance Imaging (MRI) is one of the most versatile among the various tomographic techniques suitable for process engineering applications. It leverages the nuclear magnetic resonance (NMR) phenomenon [2,3] to measure flow, diffusion, chemical composition, and temperature with high spatial and temporal resolution. Recent advancements have expanded its use in process engineering [4,5], enabling investigations into phase distributions, microreactor flows, and packed bed dynamics. To improve the signal-to-noise ratio (SNR) and temporal resolution of MRI systems, multiple receiver coils can be placed around the object to acquire the signal in parallel. Since MRI has been primarily applied in medical domain, the existing coil arrays are developed for human anatomies. In this work, we build custom coil arrays tailored to chemical reactors and investigate the impact of receiver coil density on MRI-based velocity measurements using the world’s largest vertical 3 Tesla MRI scanner. We compare 5-channel and 15-channel receive arrays to evaluate their performance in capturing flow behavior within structured packings with Schwarz-Diamond-Triply Periodic Surface (TPSf) designs, relevant to chemical engineering. Initial velocity measurements in water phantoms reveal that the 15-channel array significantly improves spatial resolution and SNR over the 5-channel configuration. These enhancements enable detailed mapping of velocity fields, finer resolution of flow dynamics, and improved visualization of mixing and bubble interactions within complex geometries. References [1] Weiland, C., Steuwe, E., Fitschen, J., Hoffmann, M., Schlüter, M., Padberg-Gehle, K., & von Kameke, A. Computational study of three-dimensional Lagrangian transport and mixing in a stirred tank reactor. Chemical engineering journal advances. 2023, 14. Jg., S. 100448 https://doi.org/10.1016/j.ceja.2023.100448 [2] Rabi, I. I.; Zacharias, J. R.; Millman, S.; Kusch, P. A New Method of Measuring Nuclear Magnetic Moment. Phys. Rev. 1938, 53 (4), 318–318. https://doi.org/10.1103/PhysRev.53.318. [3] Bloch, F. Nuclear Induction. Phys. Rev. 1946, 70 (7–8), 460–474. https://doi.org/10.1103/PhysRev.70.460. [4] Benders, S.; Blümich, B. Applications of Magnetic Resonance Imaging in Chemical Engineering. Phys. Sci. Rev. 2019, 4 (10). https://doi.org/10.1515/psr-2018-0177. [5] Gladden, L. F.; Sederman, A. J. Recent Advances in Flow MRI. J. Magn. Reson. 2013, 229, 2–11. https://doi.org/10.1016/j.jmr.2012.11.022.Publicationtype: Conference Poster46 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Influence of counterdiffusion effects on mass transfer coefficients in stirred tank reactors(Elsevier, 2021-09-06); ; ; ; Accurate knowledge of volumetric oxygen mass transfer coefficients in multiphase systems is important for successfully designing and efficient operation of process plants. As a result, a large number of papers on the determination of volumetric mass transfer coefficients kLa have been published in the literature. The dynamic degassing method is probably the most common method for determining the volumetric mass transfer coefficient. However, little work is known on the influence of countercurrent diffusion effects, arising from further dissolved components, on the volumetric mass transfer coefficient. For this reason, the effect of countercurrent diffusion is investigated in the present work by using different stripping gases to determine the volumetric oxygen mass transfer coefficient. Furthermore, the effect of counterdiffusion is investigated for both conventional aeration and aeration with microbubbles. The present work shows that the choice of stripping gas has a decisive influence on the determination of the volumetric oxygen mass transfer coefficient. Moreover, it can be shown that this effect is directly proportional to the solubility of the stripping gas in the aqueous phase. Simultaneous measurements of bubble size distributions allow determining mass transfer coefficients kL. A model is developed describing the decrease in the mass transfer coefficient as a function of the solubility of the stripping gas. Furthermore, it can be shown that for the experimental determination of volumetric oxygen mass transfer coefficients, the choice of stripping gas should be adapted to secondary gas types occurring within real processes achieving a better comparability.Publicationtype: Journal ArticleScopus© Citations 1 63 401 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimentelle Untersuchung des Stofftransports im mikroblasenbegasten Rührreaktor unter der Berücksichtigung von Gegendiffusionseffekten(2020-10); Many chemical and biological liquid phase reactions require gaseous components provided by aeration via gassed stirred tanks. For fast chemical and biological reactions mass transfer from the gas to the liquid phase is often limited making a continuous process optimisation necessary. For this process optimisation, the mass transfer is usually quantified in the laboratory via the volumetric mass transfer coefficient kLa using the measurement method of gas stripping with nitrogen. The present work focuses on the characterisation of counter-diffusion effects and their influence on mass transport. The influence of different stripping gases on the determination of the kLa-value is particular important. The basis of this work is a 2 L stirred reactor and three gassing devices (opentube, L-sparger and sintered frit). These sparger can be differentiated primarily by their bubble size and shape. The analysis of mass transfer with different degassing methods is performed by the oxygen kLa-value for different gas volume flows and gassing devices. The reaction medium is stripped via nitrogen or argon. A physically degassed medium is used as well. In addition to mass transport measurements, endoscopic measurements are used to record the micro-bubbles generated by the sintered frit. As a key-result of the investigations, the physically degassed medium shows 56% higher mass transport rates than the medium desorbed with nitrogen. The main reason is the counter-diffusion and the resulting lower oxygen partial pressure in the bubbles, which has a negative influence on the mass transport. Moreover, the counter-diffusion effects increase with higher gas solubility of the stripping gas and mass transfer rate of oxygen decreases. In addition, the endoscopic measurement data and the kLa-values were used to calculate the respective mass transfer coefficients kL. These are characteristic for each degassing method. On the basis of the kLa-values a model for quantifying the counter-diffusion effects could be developed.Publicationtype: Bachelor Thesis302 1820