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Item type:Publication, Access status: with files , Powering mobile sensor nodes in fluidized beds: A non-invasive RF energy harvesting proof-of-concept(American Chemical Society (ACS), 2026-10-16); ; ; ; Real-time monitoring within industrial processing vessels is essential for advancing process analytical technology. Flow-following sensors represent an ideal approach for delivering continuous, in-line data from the process stream. However, deploying these mobile sensors is constrained by the physical barriers of sealed metallic vessels and harsh, battery-hostile environments. To overcome these limitations, a non-invasive, retrofittable wireless power transfer system is presented. The metallic vessel is structurally repurposed into a 5.23 GHz multi-mode microwave cavity resonator by coupling microwave energy through existing standard flanges. Electromagnetic simulations validate that this method generates continuous energy coverage throughout dynamic flow zones, demonstrated using a fluidized bed granulator as an application example. To harness this energy, an omnidirectional antenna and a compact RF-to-DC rectifier prototype were developed. By enabling the continuous operation of autonomous, battery-free mobile sensor nodes, this framework provides a practical, scalable foundation for high-density spatial analytics and data-driven industrial optimization.Publicationtype: Journal Article18 9 - Some of the metrics are blocked by yourconsent settings
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 , Millimeter-scale Lagrangian sensor spheres for local state monitoring in SMART reactors: towards energy-autonomous operation(American Chemical Society (ACS), 2026-09-18); ; ; ; Flow-following sensor particles are a promising route to obtaining spatially resolved measurements in (bio)chemical reactors. However, their practical deployment is limited by miniaturization, power supply, and packaging. This work presents a millimeter-scale Lagrangian sensor-node platform that integrates an inertial measurement unit (IMU) and a low-power microcontroller unit (MCU) on a high-density interconnect (HDI) printed circuit board (PCB), illustrating the evolution from a first demonstrator (V1) toward a reduced-footprint design (V2) intended for spherical encapsulation. The main contribution is a quantitative system-level feasibility boundary that links miniaturized sensor-node design, duty-cycled energy demand, candidate energy-input routes, and spherical packaging constraints at the targeted millimeter scale. We analyze the baseline power demand of the current duty-cycled implementation, including a cycle-based charge and energy budget, and relate this demand to two experimentally investigated energy-input routes: photovoltaic harvesting under controlled optical illumination and resonant inductive power transfer at 13.56 MHz. The harvesting experiments are performed on dedicated evaluation platforms and are used to quantify candidate energy-input routes. A closed energy-autonomous sensor-in-flow demonstration is not yet claimed. The results show that the platform concept, compact HDI integration, low-power duty cycling, optical data transmission, and a glass-based encapsulation route are technically feasible at the targeted size. At the same time, neither harvesting route yet closes the gap to robust energy-autonomous operation under realistic reactor conditions. Photovoltaic powering appears strongly constrained by alignment, optical access, and geometric coupling. Inductive transfer is more promising but remains highly sensitive to orientation, field distribution, and RF-to-DC conversion efficiency. The presented measurements therefore define both the current feasibility range and the remaining engineering requirements for future energy-autonomous sensor spheres.Publicationtype: Journal Article42 22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Reconstruction-free EIT for injection-pattern classification and superficial gas velocity regression as proxies for local gas holdup in bubble columns(American Chemical Society (ACS), 2026-09-10); ; ; ; Electrical impedance tomography (EIT) as a noninvasive tomographic technique is increasingly applied to multiphase reactor monitoring; however, conventional image reconstruction is ill-posed and regularization-dependent and may be redundant in applications where the primary objective is operating-state identification rather than explicit spatial conductivity field reconstruction. Here, we present a reconstruction-free, measurement-domain framework for bubble-column monitoring that maps raw complex boundary impedance data directly to two reactor-relevant inference tasks: (i) gas injection pattern classification and (ii) superficial gas velocities regression. Together, these two quantities ─ the spatial injection distribution and the total volumetric flow ─ constitute the primary process-state information from which gas holdup can subsequently be inferred and are therefore reported as proxies for local gas holdup monitoring. Experiments were conducted in an acrylic bubble column (600 mm height, 104 mm inner diameter) equipped with a 256-electrode array distributed over eight axial rings and operated at four excitation frequencies (1 kHz-1 MHz). Experiments covered gas flow rates between 1.0 and 6.5 L min–1 (Ug = 1.96 → 12.75 mm s–1), within which near-perfect gas injection pattern classification was achieved with accuracies of 93–100% for excitation frequencies between 1 and 100 kHz using the full 256-electrode configuration. For quantitative superficial gas velocity estimation, increasing calibration density along Ug reduced the mean absolute error from 0.388 to 0.105 L min–1 (MAE[Ug] = 0.76 → 0.205 mm s–1, i.e. 7.0% → 1.9% of the operating range) for localized injection and from 0.298 to 0.157 L min–1 (MAE[Ug] = 0.585 → 0.307 mm s–1, i.e. 5.4% → 2.8% of the operating range) for distributed injection conditions. These results demonstrate that direct inference from raw EIT boundary measurements enables accurate, real-time monitoring of bubble-column operation without tomographic reconstruction and provide quantitative guidance on excitation frequency selection, axial sensing placement, and calibration resolution.Publicationtype: Journal Article28 27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Advanced micromolding approach toward scaling-up smart hydrogel microvalves(American Chemical Society (ACS), 2026-09-09); ; ; Smart hydrogel valves are a promising technology for autonomous process control. At the macroscale, hydrogel valves offer high flow rates with slow response times, whereas hydrogel microvalves offer low flow rates with fast response times. This contradiction limits the practical applicability of these valves, particularly in industry. Scaling-up refers to the process of transferring the benefits and results of microfluidics from the laboratory scale to the production scale. In this paper, we present advanced fabrication methods and corresponding promising concepts toward scaling-up responsive hydrogel microvalves to achieve higher throughput while maintaining fast response times. Using selective laser-induced etching (SLE), precise three-dimensional (3D) microfluidic structures and corresponding molds can be produced from fused silica, allowing hydrogel to be molded and anchored directly within the microchannel. This method enables the sizing-up of hydrogel microstructures in both horizontal and vertical directions. The influence of this scaling, in the form of various hydrogel dimensions up to 1500 μm, was investigated with regard to their suitability for an autonomous hydrogel valve. As a proof-of-principle, three hydrogel valves with different depths were fabricated using this method, whereby the response time decreases with increasing depth while the flow rate is increased simultaneously.Publicationtype: Journal Article84 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Dynamical compartments in stirred tank reactors and Markov state modeling for mixing quantification: A transfer operator approach(American Chemical Society (ACS), 2026-08-31); ; ; ; Identifying coherent flow structures in chemical reactors is crucial for understanding the mixing dynamics, which is essential for optimizing reactor performance. We demonstrate the use of a transfer operator method to find coherent flow structures such as almost-invariant sets and coherent sets, which are characterized by minimal mixing with the surrounding fluid, in a lab-scaled stirred tank reactor using both simulated and experimental Lagrangian trajectory data. The proposed method further enables a detailed analysis of the mixing behavior by computing expected residence times and mixing times. Additionally, a Markov state model describes the macroscopic transport dynamics between compartments in the reactor.Publicationtype: Journal Article57 20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Aerographite vs Graphite: Investigating the role of electrode architecture in H2-mediated electroautotrophic biofilms(American Chemical Society (ACS), 2026-08-07); ; ; ; Oxic microbial electrosynthesis using aerobic hydrogenotrophic bacteria requires productive cathodic biofilm formation, yet reactive oxygen species (ROS) generated at the electrode surface present a critical barrier to initial colonization. This study investigates biofilm development by Cupriavidus necator H16 on Aerographite, an ultralow-density carbon foam (3–12 mg cm–3, porosity > 99%) with a hierarchical tetrapodal pore network, as a cathode material in microfluidic bioelectrochemical systems and compares it to graphite (a composite material consisting of graphite and polypropylene (PPG86)). A biphasic cultivation strategy, in which heterotrophic biofilm establishment preceded a switch to electroautotrophic conditions at −45.45 μA cm–2, successfully overcame the ROS barrier on both electrode materials. Noninvasive optical coherence tomography revealed a final biovolume of 0.086 mm3 mm–2 on graphite after 14 days, representing the first continuous kinetic characterization of C. necator cathode biofilm formation under defined flow conditions. Despite lower absolute biovolume per projected area, Aerographite supported higher biomass per unit electrode mass, reflecting its 585-fold higher mass-specific electroactive surface area relative to graphite. Scanning electron microscopy confirmed C. necator colonization of internal pore regions up to 500 μm below the electrode surface under laminar flow-over conditions. The macropore dimensions substantially exceed documented self-limiting biofilm thicknesses, indicating that pore occlusion is unlikely even at full biofilm development, and positioning Aerographite as a structurally enabling electrode material for smart, scalable, flow-through CO2 valorization systems.Publicationtype: Journal Article70 25 - 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 Article88 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A cost-efficient electrical impedance tomography system for adaptive process analytics(American Chemical Society (ACS), 2026-08-02); ; ; ; Electrical impedance tomography (EIT) has significant potential as a noninvasive tool for spatially resolved process monitoring, yet most reported systems remain laboratory prototypes and are rarely suitable for integration into chemical engineering environments. We present a fully embedded, low-cost EIT platform designed as a deployable tomographic sensor for in situ monitoring of reactive media in laboratory-scale reactors. The platform can be realized for approximately $442 in prototype quantities and below $310 in small-batch production. The system enables spatially resolved conductivity mapping with 32 measurement channels and is designed for straightforward integration into laboratory and reactor environments. Its compact USB-powered hardware is complemented by microcontroller firmware in C and an object-oriented Python interface for experiment control and data analysis. On-board impedance calculation allows stand-alone operation and supports real-time monitoring of dynamic conductive processes. Hardware characterization includes measurements of total harmonic distortion plus noise for signal excitation and voltage measurement with mean values up to 0.0651%, a signal frequency of 105 kHz and optimized analogue amplification across all gain settings, a variable analogue filter gain ranging from −1.35 to 34.81 dB, and characterization of the current source at excitation currents of 100 and 350 μA. Additionally, the system’s performance is validated for the adjacent and opposed pair pattern, achieving a mean signal-to-noise ratio of up to 76.59 dB. The imaging performance is quantified on circular phantoms in terms of position error, spatial resolution, and detection limit, and the long-term stability is verified over a 20-h measurement with a relative drift below 0.03%. The system achieves frame rates of 7.36 to 13.18 fps depending on the measurement pattern. The system is validated in a chemically relevant scenario by monitoring the dissolution of 5 mol L–1 H2SO4(aq). The resulting spatial conductivity maps resolve transient concentration gradients associated with proton activity, illustrating the potential of the platform for the detection of local process states in adaptive reactor environments. Together, the characterized hardware performance and validation under chemically relevant conditions establish the platform as a scalable in situ imaging sensor suitable for integration into adaptive, data-driven reactor systems.Publicationtype: Journal Article28 28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Lyogel equilibria with Helmholtz equations of state. Part II: Assessment of PC-SAFT parametrizations and network models for pNIPAM Lyogels(American Chemical Society (ACS), 2026-08-02); ; This work investigates the equilibrium swelling of poly(N-isopropylacrylamide) (pNIPAM)-based lyogels in multicomponent solvent systems using a Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT)-based thermodynamic framework coupled with polymer-network elasticity. Literature parameter sets for the butyl esterification system were assessed and refined, and different network models were compared within a sequential fitting strategy that links solvent, polymer-solution, and gel data. The results show that the framework can reproduce key swelling trends and supports the transfer of calibrated network parameters between related solvent descriptions. At the same time, the study highlights important limitations: quantitative fitting of lower critical solution temperature (LCST) behavior requires a temperature-dependent interaction parameter, finite-extensibility effects are negligible for the investigated systems, and the transferability of fitted interaction parameters to mixed solvents is limited. Overall, the work provides a practical framework for gel-equilibrium calculations while emphasizing the need for careful interpretation of fitted parameters.Publicationtype: Journal Article31 27