Universität Stuttgart
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Item Open Access Modelling pore size distribution function of twist-texturized yarns and single-jersey knitted fabrics(2025) Pauly, Leon; Maier, Lukas; Schmied, Sibylle; Dinkelmann, Albrecht; Nieken, Ulrich; Gresser, Götz T.Pore sizes on the micrometre scale are a critical factor influencing the fluid transport properties of textiles. Consequently, the pore size distribution function is a desirable parameter in the design of textiles for technical applications. However, the experimental determination of pore size and its distribution can be challenging, costly, or impractical. Knitted fabrics offer a wide range of porosity and pore size distribution properties. While statistical models have shown reasonable accuracy in predicting pore size distributions in nonwovens and filter media, no equivalent model exists for twist-texturized yarns and single-jersey knitted fabrics. This study presents a hierarchical pore model for single-jersey fabrics. The model uses a log-normal distribution for the intra-yarn pores in the yarn and cylindrical pores for inter-yarn pores between the yarns in the fabric. With these two pore sizes, the model quantitatively characterises the porous structure of the fabric. Initial validation of the model for intra-yarn pores on four yarns of different fibre finenesses shows that the model can cover the influence of different fibre counts. For the validation on the fabric scale, two tomography datasets of single-jersey knitted fabrics show that the presented model can capture the effect of different fabric structures. A parameter study visualises the effects of both yarn and knitting parameters on the pore size distribution function of single-jersey knitted fabrics. The mean pore sizes of the fabrics are given. The results deepen the understanding of the porous properties of knitted fabrics and provide a valuable direction for structural fabric development on knitting machines.Item Open Access Convective drying of porous media : comparison of phase-field simulations with microfluidic experiments(2024) Maier, Lukas; Brosch, Sebastian; Gaehr, Magnus; Linkhorst, John; Wessling, Matthias; Nieken, UlrichConvective drying of porous media is central to many engineering applications, ranging from spray drying over water management in fuel cells to food drying. To improve these processes, a deep understanding of drying phenomena in porous media is crucial. Therefore, detailed simulation of multiphase flows with phase change is of great importance to investigate the complex processes involved in drying porous media. While many studies aim to access the phenomena solely by simulations, here we succeed to compare comprehensively simulations with an experimental methodology based on microfluidic multiphase flow studies in engineered porous media. In this contribution, we propose a Navier-Stokes Cahn-Hilliard model coupled with balance equations for heat and moisture to simulate the two-phase flow with phase change. The phase distribution of the two fluids air and water is modeled by the Phase-Field equation. Comparisons with experiments are rare in the literature and usually involve very simple cases. We compare our simulation with convective drying experiments of porous media. Experimentally, the interface propagation of the water-air interface was visualized in detail during drying in a structured microfluidic cell made from PDMS. The drying pattern and the drying time in the experiment are very well reproduced by our simulation. This validation will enable the application for the presented Navier-Stokes Cahn-Hilliard model in more complex cases focused more on applications, e.g., in the field of fibrous materials.Item Open Access Synthesis and characterization of novel perfluoro aromatic side chain sulfonated PSU ionomers(2024) Martschin, Philipp; Atanasov, Vladimir; Thiele, Simon; Kerres, JochenPolyethersulfone (PSU) as a commercially available polymer offers many different opportunities for functionalization for diverse fields of application, for example, electrophilic substitutions like sulfonation and bromination or nucleophilic reactions such as lithiation. This study presents three different polysulfone derivatives, first functionalized by a lithiation reaction, followed by a reaction with carbonyl compounds containing pentafluorophenyl groups. In the last step, the pentafluorophenyl moieties of the modified PSU were sulfonated by thiolation and subsequent oxidation to sulfonic acid groups. Those novel PSU derivatives were characterized by NMR, DSC, TGA, GPC, and titration. Based on these ionomers, we show the fabrication of pure and acid-base blend membranes with promising proton conductivities. These novel sulfonic acid groups containing materials are potentially promising candidates for membranes or ionomers in electrochemical applications such as proton exchange membrane fuel cells (PEMFCs), proton exchange membrane water electrolysis (PEMWEs), or redox flow batteries (RFBs).Item Open Access Oxidation of carbonaceous nanoparticles : reactivity and structural evolution(2026) Raiolo, Antonio; Nieken, Ulrich (Prof. Dr.-Ing.)Item Open Access Centralized nonlinear model predictive control for energy efficient thermal management in battery electric vehicles(2025) Misznéder, Marcell; Rengstl, Ulrich; Hopp-Hirschler, Manuel; Nieken, UlrichThermal management is a key factor for the efficiency, performance, and reliability of battery electric vehicles (BEVs), particularly in systems with strongly coupled components and heterogeneous thermal dynamics. This study proposes a centralized nonlinear model predictive control (NMPC) strategy for component cooling in BEVs, designed to maintain temperatures within optimal ranges while minimizing energy consumption and respecting actuator constraints. A reduced-order physics-based model is developed in MATLAB/Simulink R2024b, and the NMPC is implemented using CasADi, incorporating coolant temperatures as stabilizing states and a systematic parametrization of sampling time, prediction horizon, and weighting factors. The considered thermal management system consists of hydraulically coupled subsystems with different overall time constants, for which a single-horizon NMPC formulation is applied. Simulation results show that the proposed controller accurately tracks thermal dynamics across components with varying inertia and effectively captures cross-coupling effects. Sensitivity analyses indicate that variations in sampling time and prediction horizon have a limited impact on temperature trajectories and energy consumption, demonstrating robustness and real-time applicability. Compared to a rule-based controller, the NMPC achieves up to 30% reduction in energy consumption depending on ambient conditions and driving cycles, while improving temperature regulation, particularly for the high-voltage battery, with up to 2 K lower peak temperatures and a more balanced temperature distribution. These findings demonstrate that centralized NMPC is a suitable and efficient approach for thermal management in directly coupled BEV subsystems with heterogeneous dynamics.Item Open Access Electrically heated multilayer ceramic composite tubes for high‐temperature endothermic reactions(2025) Kleschew, Daniel; Sentko, Matthias; Nieken, UlrichA high‐temperature reactor concept using electrically heated oxide ceramic tubes is investigated with the aim of replacing fossil fuels with renewable electricity and reducing CO₂ emissions in the chemical industry. The multilayer ceramic composite tubes are resistant to thermal stress and consist of an inner monolithic oxide ceramic, a thin metallic heating element, and an outer Al₂O₃/Al₂O₃ ceramic matrix composite (OCMC) layer. Dry reforming of methane was tested up to 1150 °C, with and without catalyst. Due to the non‐gas‐tight OCMC layer, process conditions had to be adjusted to prevent soot formation on the heater. A tube‐in‐tube design allows for heat recovery and reduces the outlet temperatures. Conversion rates of up to 80 % have been achieved, but temperature drops due to the endothermic reaction can lead to secondary soot forming conditions.Item Open Access Modellbasierte und experimentelle Analyse von drahtgewebebasierten Mikrowärmeübertragern für die chemische Reaktionstechnik(2025) Walter, Christian; Nieken, Ulrich (Prof. Dr.-Ing.)Item Open Access Polymer fouling in tubular reactors for radical polymerizations(2024) Welzel, Stefan; Nieken, Ulrich (Prof. Dr.-Ing.)Item Open Access Proton-conducting (blend) membranes based on sulfonated/phosphonated and basic polymers(2024) De Azpiazu Nadal, Ignasi; Tovar, Günter (Prof.)Aiming at new proton-conducting membranes, this thesis deals with the syntheses and characterizations of highly sulfonated poly(arylene sulfides) and other polysulfides for application as polymer electrolytes. The study focuses mainly on the analysis of the polymer structures that would improve the conductivity of current proton conducting membranes while maintaining their mechanical stability. In a first step, several polymers are obtained from which poly(arylene sulfide)s polymers look more promising for further functionalization. They are obtained by using mild reaction conditions of a polycondensation reaction between 4,4 ́-thiobisbenzenethiol (TBBT) and decafluorobiphenyl. Optimization of this reaction allows for the obtainment of higher molecular weights than the ones reported in the literature. In a second step, poly(arylene sulfides) were phosphonated and sulfonated by a nucleophilic aromatic substitution (SNAr) displacement reaction of the fluorine atoms of the fluorinated polymer sub-units using different agents. Highly sulfonated polymers were obtained when using sodium 3-mercapto-1-propanesulfonate and resulted in water soluble ionomers. Kinetic studies of this reaction were performed and several new sulfonated poly(arylene sulfides) were obtained. Finally, stable polymer electrolyte membrane (PEM) with enhanced mechanical and chemical stability were obtained by blending these obtained ionomers with polybenzimidazole (PBIOO). These membranes were further characterized and in the best case a PEM with new sulfonated ionomer showed a conductivity 40 % higher than Nafion 212, used as a golden reference material. The best performing PEM’s obtained were further used in an electrolytic cell being part of eSCALED, a H2020 (MSC-ITN-2017. GA# 765376) European project which aim is to obtain a device that does the artificial photosynthesis in a more efficient way than the current devices.Item Open Access Fouling during polymerization in different continuous reactor setups(2024) Welzel, Stefan; Nieken, UlrichFouling in continuous reactors presents a significant challenge in the process intensification of specialty polymers. While in continuous stirred tank reactors (CSTRs) fouling is minimal, tubular reactors experience severe fouling, sometimes leading to complete blockage. Therefore, it is crucial to understand process and design conditions contributing to deposit formation. In this work, the impact of geometry, mixing elements, novel coatings, and ultrasonic waves are tested on tubular reactors for the polymerization of polyvinylpyrrolidone.