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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 Article40 13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Can we live Danckwerts' dream? Mixing analysis in a baffled stirred tank reactor based on 4D-particle tracking experiments(2026-07-29); ; ; ; We present an experimental investigation of mixing dynamics within a laboratory-scale 3-liter stirred tank reactor (STR) equipped with two Rushton turbines and three baffles. Using time-resolved, four-dimensional particle tracking velocimetry, we successfully capture trajectories of up to 40,000 tracer particles in the full reactor volume despite obstructions by stirrer and baffles, providing unprecedented time-resolved flow and mixing information. From these Lagrangian data, we analyze velocities, accelerations, and spatial dispersion, revealing anisotropic mixing. By utilizing novel network-based analysis methods on the experimental particle trajectories, we identify coherent fluid compartments that exhibit strong internal mixing but weak exchange with neighboring compartments. We uncover five distinct compartments acting as transport barriers, which have a high impact on substrate distribution in chemical and biochemical processes. Our approach thus realizes and extends early thought experiments from Danckwerts and Levenspiel by providing detailed insight into the behavior of single fluid parcels and Lagrangian mixing withing chemical and biochemical reactors, offering a valuable approach for evaluation and optimization of chemical and biochemical processes. The trajectory data are made freely available to serve as an experimental reference for further research.Publicationtype: Preprint28 24 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimental analysis of time resolved three-dimensional velocity and vorticity fields behind single rising bubbles using Lagrangian particle tracking velocimetry(Elsevier, 2026-01-29); ; ; ; The present study utilizes highly resolved Lagrange particle tracking measurements to analyze the time-dependent three-dimensional fluid dynamics in the wake of air bubbles rising in quiescent bidistilled water. Two bubble sizes are studied with regard to the velocity fields and the temporal evolution of the generated vorticity in their wakes. The range of bubble sizes is of particular interest, as it corresponds to other recent studies. The bubbles are reconstructed in three dimensions to determine the bubble rise trajectory and the bubble shape. The analysis of the aforementioned measurements, particularly the calculation of the Q-criterion, supports prior numerical findings of a wake mode exhibiting secondary vortex loops. Additionally, the energy spectra of the velocity fields and their temporal evolution are analyzed, providing a unique experimental dataset for the validation of numerical simulations and the further study of bubbly flows.Publicationtype: Journal Article148 58