Zugl.: Stuttgart, Universiẗat, Diss., 2007.

Zugl.: Karlsruhe, Universiẗat, Diss., 2007.

Jet pumps are among the components of automotive FC systems (FCS) whose design need to be optimally tailored in order to improve the system efficiency. We had concluded that the ejector CFD model needed to optimize the design had to meet the requirements of being both complete enough, so that a realistic simulation of the FC system is attained, and computationally light, so that the CFD computations could be run embeded into real-time dynamic simulations of the FCS anode loop. Whereas we previously employed unstructured tetrahedral meshes, leading to excessive cell counts, our present work involves block-structured grids of purely hexahedral cells, resulting in a cell count an order of magnitude smaller. To ease our block-structure strategy, the previous geometry was slightly simplified. Our results agree with performance data already published. / Strahlpumpen gehören zu den Komponenten von Automotive FC-Systemen (FCS), deren Konstruktion optimal zugeschnitten werden muss, um die Systemeffizienz zu verbessern. Wir hatten zu dem Schluss gekommen, dass das Ejector CFD-Modell, das zur Optimierung des Designs benötigte, die Anforderungen des Seins vollständig genug erfüllen musste, so dass eine realistische Simulation des FC-Systems erreicht wird, und rechenlich leicht, so dass die CFD-Berechnungen eingebettet werden könnten Echtzeit-dynamische Simulationen der FCS-Anodenschleife. Während wir zuvor unstrukturierte Tetraedral-Meshes eingesetzt hatten, was zu übermäßigen Zellzählungen führte, beinhaltet unsere vorliegende Arbeit blockstrukturierte Gitter aus rein hexaedrischen Zellen, was zu einer Zelle führt, die eine größere Größenordnung darstellt. Um unsere Blockstrukturstrategie zu erleichtern, wurde die vorherige Geometrie leicht vereinfacht. Unsere Ergebnisse stimmen mit bereits veröffentlichten Leistungsdaten überein.

A passive recirculation of hydrogen using ejectors is effective and efficient only in a limited operating window, which kept ejectors until recently from being integrated into automotive fuel cell systems, where a more dynamic operation is expected. Strategies like parallel setup or a PWM-drive employed to expand the operating window demand reliable control algorithms. Such algorithms can greatly benefit from the predictive power a mathematical model. In a fuel cell system, the anode and cathode side cannot be separated, and a mathematical description should encompass all components to a reasonable degree, to allow the model to run on a low power automotive-grade platform in real time. This contribution demonstrates an approach to reduce the computation expense of the mathematical model.

High-Pressure Partial Oxidation (HP-POX) of natural gas is one of the techniques in the synthesis gas production by non-catalytic reforming. On the path to emissions reduction, all operating facilities must be optimized to satisfy environmental regulations. In a rapidly changing economic and political environment, technological development from lab-scale to demo-scale, and industrial-scale is no longer feasible. Therefore, new research and design methods must be applied. One of such methods commonly used in science and industry is numerical modeling, which utilizes Computational Fluid Dynamics (CFD), Reduce Order Models (ROMs), kinetic, and equilibrium models. The CFD models provide details about flow field, temperature distribution, and species conversion. However, the computational effort required to conduct such calculations is significant. The computationally expensive CFD models cannot be effectively used in the reactor optimization. Herewith, other modeling techniques utilizing kinetic and equilibrium models do not provide necessary details for process optimization and can only be used for adjustments of boundary conditions, investigation of specific processes occurring in the reactor, or development of sub-models for CFD. A numerical investigation was conducted to validate existing CFD models against benchmark experiments. The results reveled that the CFD model is sensitive to modeling parameters, when simulating complex flows where turbulence-chemistry interaction occurs. Moreover, it was shown that the results sensitivity increases along with the oxidizer/fuel inlet velocities ratio. Based on the conducted experiments, the CFD model validation resulted in definition of the modeling parameters suitable for modeling of HP-POX of natural gas. Based on the validated CFD model, a ROM for HP-POX of natural gas was developed. The model assumes that the reactor consists of several zones characterized by specific conversion processes. Moreover, the model considers inlet streams dissipation upon the injection, and includes several optimization stages that allows model adjustments for any reactor geometry and boundary conditions. It was shown that the developed ROM can reproduce global reactor characteristics at non-equilibrium conditions unlike other ROMs, kinetic, or equilibrium models. Moreover, the validation against CFD results showed that the ROM can correctly account for the \gls{rtd} in the reactors of different geometries and volumes without extensive additional optimization. Finally, new experiments were designed and conduced at semi-industrial HP-POX facility at TU Bergakademie Freiberg. The experiments aimed to study the influence of different oxidizer/fuel velocities ratios on the reactants mixing and process characteristics at high operating pressures. The high velocity difference between oxidizer and fuel was achieved by injection of High-Velocity Oxidizer (HVO). The experiments showed no significant influence of the HVO on the global reactor characteristics and overall species conversion process. However, the numerical analysis of the experimental results demonstrated that the oxidation zone is affected by the oxidizer inlet velocity, and becomes less efficient in the fuel conversion when the oxidizer/fuel inlet velocities ratio is increased. In summary, a sophisticated numerical model validation was conducted and sensitivity of the numerical results to the modeling parameters was carefully studied. The novel natural gas conversion technique was experimentally studied. Based on the conducted experiments and numerical evaluation a ROM was developed. The ROM is capable of producing high accuracy results and greatly decreases the computational effort and time needed for reactor development and optimization.

Im Rahmen des ZIM-geförderten Vorhabens „Rezirkulationsgebläse-Entwicklung für die Brennstoffzellen-Technologie“ (REZEBT) wurde die Entwicklung eines neuartigen aktiven Wasserstoff-Rezirkulationsgebläses für die Anodenseite einer Brennstoffzelle bis TRL4 vorangetrieben. Das vorgestellte Gebläse besteht im Wesentlichen aus einem schnelldrehenden Turboverdichter, welcher mit einem sogenannten Medienspaltmotor angetrieben wird. Der Medienspaltmotor zeichnet sich dadurch aus, dass er das Medium durch den Spalt zwischen Rotor und Stator fördert, wodurch gänzlich auf dynamische Dichtungen verzichtet werden kann und das Medium selbst zur Kühlung genutzt werden kann. Bauartbedingt kann bei diesem permanent-erregten Synchronmotor (sensorlos) auf eine aufwändige Konstruktion und teure Produktionsprozesse verzichtet werden. Diese Veröffentlichung beschreibt den Prozess und die Herausforderungen der Auslegung sowie den Aufbau des Anodenrezirkulationsgebläses (ARG). Die Funktionsfähigkeit wurde mittels eines Prototypen demonstriert.