Eldorado - Repositorium der TU Dortmund

Ressourcen aus und für Forschung, Lehre und Studium

Bei diesem Service handelt es sich um das Institutionelle Repositorium der Technischen Universität Dortmund. Hier werden Ressourcen aus und für Lehre, Studium und Forschung gespeichert, erschlossen und der Öffentlichkeit zugänglich gemacht.

Hauptbereiche in Eldorado

Wählen Sie einen Bereich, um dessen Inhalt anzusehen.

Gerade angezeigt 1 - 5 von 9

Fach- und Universitätsübergreifendes 1320
Fakultäten 14057
Graduate School und Graduiertenkollegs 12
Hochschulverwaltung 1258
Sonderforschungsbereiche 1595

Aktuellste Veröffentlichungen

CFD simulation of methane pyrolysis in plasma reactor for CO₂-free hydrogen
(2026) Magazova, Aliya; Diéguez Alonso, Alba; Agar, David W.
Reducing greenhouse gas emissions and slowing global warming are among today’s most pressing challenges, particularly in the industrial, transportation, and agricultural sectors. One promising solution is the transition to hydrogen as a clean energy carrier. Among the various methods of hydrogen production, turquoise hydrogen, generated through methane pyrolysis, offers a promising pathway to reduce carbon emissions. When this process is carried out in plasma reactors powered by renewable energy, it enables the production of CO₂-free hydrogen. This work presents CFD simulations of methane pyrolysis in two types of plasma reactors: gliding arc plasma (GAP) and microwave plasma (MW). The 0D sensitivity analyses revealed that thermal reactions dominate over electron impact reactions due to high plasma temperatures (3000 – 4000 K). Consequently, in more detailed 2D and 3D simulations, plasma was modeled as a heat source to explore the reaction dynamics and optimize reactor design and operating conditions. In these models, the MW plasma was represented by a Gaussian heat peak, while the GAP plasma was modeled as an “artificial arc”. This approach improved methane conversion in the GAP reactor from 35 to 44 %. The simulation also identified the zones of increased by-product formation within the MW plasma reactor. These findings can inform future improvements in reactor design, helping to enhance overall efficiency. Additionally, simulations were conducted for surface dielectric barrier discharge (SDBD) plasma using a gas mixture of oxygen, nitrogen, and hydrogen. Compared to methane pyrolysis, this mixture involved fewer chemical reactions, so no simplification of the plasma modeling was necessary. The focus of the simulation was on the plasma discharge effects, specifically the influence of ionic wind on gas conversion. Since the gas temperature in the SDBD reactor was significantly lower than in the GAP and MW reactors, the simulations clearly demonstrated the difference between cold and warm plasmas.
Towards process intensification in homogeneous catalysis
(2025) Söderholm, Viktor Karl Axel; Vogt, Dieter; Held, Christoph
The central theme of this thesis is to enhance the recyclability of homogeneous catalysts of the type phosphine/phosphite/transition-metal-complexes as well as Brønsted acids to make processes based on such catalysts ever more feasible. The initial approach was to apply organic solvent nanofiltration (OSN) membranes in conjunction with molecular weight enlargement (MWE) of the catalyst/ligands. Specifically, polyhedral oligomeric silsesquioxane (POSS) was the MWE-unit of choice. It is important to have control over the ligands/catalyst’s stability under typical reaction conditions for extended periods of time in order to justify such modifications. The stability of phosphine ligands and Brønsted acids is relatively unproblematic and so POSS modifications of such ligands was directly attempted. The stability of phosphite ligands was known to be more difficult and so this was explored more deeply. Hence, in this thesis one chapter is dedicated to study the long-term stability of the phosphite ligand Biphephos when in solution, exposed to elevated temperature and under typical Rh-catalysed hydroformylation reaction conditions. It was concluded that the way a Biphephos/Rh solution is prepared has a major impact, the use of stabilising additives is important and that using an O2-free hydroformylation system is decisive in order to achieve long-term stability of such ligands. Two chapters of this thesis were dedicated to the POSS modification of phosphine ligands. One chapter presents a set of TPP-POSS ligands bearing 1, 2 or 3 POSS cages, highlighting that grafting a POSS cage so close to the phosphorus atom can have significant effects upon the ligand’s catalytic activity. The other chapter presents work on POSS modification of Xantphos-type ligands in the rear of their ligand backbone. The synthesis of NixantPOSS, a POSS modified version of Nixantphos, was realised in a one-pot reaction at ambient temperature giving the desired ligand at 94% isolated yield. When NixantPOSS was applied in the Rh-catalysed hydroformylation reaction of 1-octene it showed the same selectivity and only an 18% reduction in TOF as compared to the unmodified Nixantphos. NixantPOSS was rejected at 99% by a ceramic nanofiltration membrane during continuous hydroformylation. The last chapter of this thesis explores the application of sulfonated octaphenyl-POSS as a Brønsted acid catalyst in the ketalisation reaction of glycerol with butanone. The H-S-POSS catalysts were almost as active as PTSA and significantly more active than Amberlyst-36. The solubility of H-S-POSS was poor in all common laboratory solvents and so a recycling strategy based upon centrifugation and sedimentation was explored that turned out successful for H-S-POSS catalyst with a lower degree of sulfonation.
Branching into uncertainty
(2026) Föge, Nico; Pauly, Markus; Doebler, Phillipp
Random Forests are widely used due to their flexibility and strong predictive performance, yet statistical inference and the treatment of missing or hierarchically structured data remain challenging. This dissertation addresses these challenges in three contributions. First, asymptotic properties of the Random Forest Permutation Importance Measure are investigated, and a central limit theorem is established, providing a theoretical foundation for statistical inference on variable importance. Second, inference for permutation importance in the presence of missing data is studied, with particular emphasis on the construction of confidence intervals. Third, tree-based multiple imputation methods are adapted to hierarchical data and systematically evaluated in a simulation study. Together, these contributions extend the applicability of Random Forest methodology beyond prediction and provide theoretical and practical tools for uncertainty quantification, inference, and imputation in complex data settings.
Efficient Geometry Representation Strategies for the Shape Optimization of Profile Extrusion Dies
(2026-09) Sasse, Jana; Esser, Maximilian; Mügge, Markus; Turek, Stefan
The design of profile extrusion dies remains a challenging task due to the complex rheological behavior of polymer melts and the geometric intricacies of flow channels. Traditional manual optimization approaches, which rely heavily on human experience, are inefficient and often employ unvalidated heuristics. To address these challenges, we present a deterministic and explainable framework for automatic die design based on adjoint-based shape optimization. This approach enables the computation of sensitivities that directly indicate beneficial modifications to the flow channel geometry. A major difficulty in such optimization processes lies in generating boundary-conforming meshes that evolve consistently with changing geometries. To overcome this issue, we employ non-boundary conforming geometry representation methods that eliminate the need for an explicit surface representation along physical boundaries. A dedicated reconstruction technique is developed to recover accurate sensitivity information at the virtual interface between fluid and solid regions. The proposed algorithm is demonstrated on 3D geometries with varying complexity, including realistic extrusion die flow channels. Several objective functionals relevant to industrial applications, such as flow balance at the outflow, are considered. The results highlight significant improvements in performance metrics while maintaining numerical robustness. This work showcases the potential of adjoint-based techniques for automated die design in a domain still largely governed by manual trial-and-error procedures, establishing a foundation for data-efficient, sustainable manufacturing workflows using computational rheology.
Oscar’s Grind Betting at Roulette
(2026-08-15) Pflaumer, Peter Oskar
Oscar’s Grind is a positive-progression betting system often perceived as a low-risk alternative to strategies such as the Martingale, owing to its conservative rules: the wager increases by only one unit after a win and remains unchanged after a loss. This paper critically evaluates the mathematical viability and long-term performance of Oscar’s Grind for even-money roulette bets, using analytical arguments and extensive Monte Carlo simulation. Results demonstrate that, despite frequent small wins and gradual progress, the system cannot overcome the house edge: long-term expected losses remain negative, and the probability of a loss after multiple sessions approaches certainty. Oscar’s Grind thus provides psychological appeal but no mathematical advantage, illustrating that gradual, conservative bets reduce short-term fluctuations but do not alter the long-term expected loss and the gambler's fallacy.