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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 , Directional dark field for nanoscale full-field transmission X-ray microscopyDark-field X-ray imaging visualizes structural inhomogeneities through small-angle scattering, but existing directional methods are confined to the micrometer scale. While recent advances have extended dark-field capabilities to nanoscale transmission X-ray microscopy, directional scattering retrieval - critical for characterizing anisotropic nanostructures - has remained inaccessible for imaging resolutions in the sub-micrometer scale. Here, we demonstrate the first directional dark-field setup for nanoimaging, achieving orientation mapping of scattering features below the spatial resolution limit. Our method is experimentally simple to implement with existing transmission X-ray microscopy setups. We validate its performance by successfully resolving sub-resolution test structure orientations, cross-correlating orientational changes within hierarchical nanoporous materials, and mapping the directional arrangement of hydroxyapatite nanocrystals 30 - 70 nm within human tooth enamel. By utilizing shadow regions in the optical configuration, we further extend the detectable scattering vector range, demonstrating a pathway toward size-selective dark-field imaging. This advancement enables the quantitative structural characterization of anisotropic nanomaterials, which are critical to biomineralization, advanced materials, and nanotechnology applications.Publicationtype: Journal Article44 44 - 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: without files , Additive manufacturing of hierarchically porous silicon and silica glass(Deutsche Gesellschaft für Materialkunde e.V. (DGM), 2026-03-24); ; ; ; Publicationtype: Conference Presentation102 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Comprehensive study of 3D liquid flow fields in additive manufactured structures for SMART reactors using large-scale vertical magnetic resonance imaging and computational fluid dynamicsTriply 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: Preprint51 25 - 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 , Simulating Gadolinium-induced magnetic field variations for temperature sensing with magneto-mechanical resonatorsSmall-size magneto-mechanical resonators (MMR) represent an emerging class of passive, wireless sensors that combine a sensing functionality with a tracking option. The operation principle is based on a resonating rotor oscillation whose frequency is defined by the magnetic flux density of a stator magnet. One general sensing mechanism is the coupling of an external parameter to this resonator frequency. In this study, we investigate an approach for encoding a temperature information as a shift in the natural oscillation frequency utilizing the temperature-dependent magnetic properties of gadolinium (Gd). We perform an isolated simulation study on the temperature scaling of the magnetic field generation for stators coated with Gd of varying thickness. Our results show that the magnetic phase transition of Gd at its Curie temperature leads to a pronounced change in the magnetic permeability enabling a significant magnetic shielding behavior only for lower temperatures. In the transition regime, we find a peak sensitivity reaching 45.8 Hz/K exceeding existing values from the literature by up to a factor of 20. The findings of this work are an important step toward quantitative high-sensitivity temperature extraction with MMRs.Publicationtype: Conference Paper95 45 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Directional dark field for nanoscale full-field transmission X-ray microscopy(2025-06-20); ; 37 15