• Energy Research
• DE close
• CH close
• AT close
• TH close
• RWTH Aachen University close

In 2008 the Large Hadron Collider (LHC) and its experiments started operation at the European Centre of Nuclear Research (CERN) in Geneva with the main aim of finding or excluding the Higgs boson. Only four years later, on the 4th of July 2012, the discovery of a Higgs-like particle was proven and first published by the two main experiments ATLAS and CMS. Even though proton–proton collisions are the main operation mode of the LHC, it also acts as an heavy-ion collider. Here, the term “heavy-ion collisions” refers to the collision between fully stripped nuclei. While the major hardware system of the LHC is compatible with heavy-ion operation, the beam dynamics and performance limits of ion beams are quite different from those of protons. Because of the higher mass and charge of the ions, beam dynamic effects like intra-beam scattering and radiation damping are stronger. Also the electromagnetic cross-sections in the collisions are larger, leading to significantly faster intensity decay and thus shorter luminosity lifetimes. As the production cross-sections for various physics processes under study of the experiments are still small at energies reachable with the LHC and because the heavy-ion run time is limited to a few days per year, it is essential to obtain the highest possible collision rate, i.e. maximise the instantaneous luminosity, in order to obtain enough events and therefore low statistical errors. Within this thesis, the past performance of the LHC in lead-lead (Pb-Pb) collisions, at a centre-of-mass energy of 2.76 TeV per colliding nucleon pair, is analysed and potential luminosity limitations are identified. Tools are developed to predict future performance and techniques are presented to further increase the luminosity. Finally, a perspective on the future of high energy heavy-ion colliders is given.

Due to the increasing demand for higher efficiencies of centrifugal compressors, numerical optimization methods are becoming more and more relevant in the design process. To identify the beneficial features of a numerical optimized compressor design, this paper analyses the influence of arbitrary blade surfaces on the loss generation in a transonic centrifugal compressor. The paper therefore focuses on an analysis of the secondary flow development within the impeller blade passages. To do this, steady simulations were performed on both a baseline and an optimized blade design. Two distinct design features of the optimized compressor stage were identified, which lead to a more homogenous impeller exit flow and thus to an increase in total-to-static efficiency of 1.76% points: the positive lean in the near-tip region and the positive blade curvature in the rear part of the optimized impeller. Furthermore, through extensive experimental investigations conducted on a large scale test rig it has been possible to prove the particular impeller outflow characteristics of the baseline compressor stage.

The working pair zeolite-water has very good characteristics for the heat pump application. It is non-poisonous, non-flammable and low-corrosive so that the use of a zeolite-water heat pump in the large field of domestic heating is very promising.

Wall heat fluxes can be derived from time resolved measurements of the surface temperature. This paper describes an analytical approach to calculate the heat flux from an analytical solution of the one-dimensional transient energy equation with transient boundary conditions using the Laplace transformation. The results are compared to simple test cases for which the heat fluxes are given in literature. The method is used to calculate the heat flux from a fuel spray to a wall at diesel engine conditions.

Increasing agricultural productivity is one of the most important aims of modern biotechnology. One way to enhance the productivity of crop species is to enhance the efficiency of photosynthesis. In C3 plants the oxygenase activity of Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) limits the photosynthetic efficiency. The green microalgae Chlamydomonas reinhardtii has evolved a CO2 concentration mechanism (CCM) by increasing the CO2 concentration in the chloroplast stroma where RuBisCO is located. Four independent transgenic tobacco genotypes (LA, LB, C1 and C3) were generated producing the low CO2-inducible protein A and B (LCIA and LCIB) or the carbonic anhydrases I and III (CAH1 and CAH3) from C. reinhardtii CCM in the envelope, stroma, intermembrane space or thylakoid lumen of tobacco chloroplasts, respectively. All four recombinant proteins were active in planta, which had a substantial impact on carbon and nitrogen metabolism. Increasing the CO2 concentration near RuBisCO resulted in an enhanced rate of photosynthesis (by up to 15%), efficiency of photosystem II (by up to 18%) and chlorophyll content (by up to 19%). Although to differing extents, all four transgenic genotypes grew faster than wild-type plants, produced more shoot biomass (up to 45% more fresh weight or 38% more dry weight in the LA lines) and accumulated more photosynthetic end products, reflecting the higher rate of photosynthetic CO2 fixation. The proteome analysis revealed that the proteins changed in the transgenic genotypes compared to the wild-type plants were primarily associated with the regulation of the Calvin cycle and the amino acid biosynthesis. Metabolic analysis of the transgenic LA, LB and C3 plants revealed an increase in the levels of carbohydrates and also of most amino acids. Furthermore, transgenic LA and LB plants could maintain the enhanced biomass under low nitrogen conditions, where similarly-treated wild-type plants grew more slowly. The data generated in the present study confirmed that even single Chlamydomonas CCM components can be integrated into C3 plants to increase biomass, suggesting that transgenic lines combining multiple components or even a complete CCM could further increase the productivity and yield of C3 crops. RWTH Aachen University, Diss., 2017; Aachen, 1 Online-Ressource (151 Seiten) : Illustrationen, Diagramme(2017). = RWTH Aachen University, Diss., 2017 Published by Aachen

Abstract A high-temperature PEFC system, developed with the aim of delivering 5 kW electrical power from the chemical energy stored in diesel and kerosene fuels for application as an auxiliary power unit, was simulated and tested. The key components of the system were an autothermal reformer, a water–gas shift reactor, a catalytic burner, and the HT-PEFC stack. The targeted power level of 5 kW was achieved using different fuels, namely GTL kerosene, BTL diesel and premium diesel. Using an integrated system approach, operation without external heat input was demonstrated. The overall analysis showed slight but non-continuous performance loss for 250 h operation time.

Applied energy 388, 125530 (2025). doi:10.1016/j.apenergy.2025.125530 Published by Elsevier Science, Amsterdam [u.a.]

Abstract The HTR Code Package (HCP) has been under development since 2010 at Forschungszentrum Julich and at Aachen University. This HCP combines the capabilities of individual legacy codes developed during the German HTR programme in a highly integrated manner and contains new features. Within the HCP, all aspects related to the fuel management are handled by SHUFLE (Software for Handling Universal Fuel Elements). In principle the module is designed to handle all kinds of fuel elements. The module depicts the pebble flow in such a way, that both the accuracy as well as calculation time constraints given by a multi-physics code package such as the HCP are met. SHUFLE offers two different fuel management models for pebble-bed reactors, the ‘flow tube model’ and the ‘seepage model’. Within this paper, the flow tube model is discussed in detail. Especially aspects such as the development, implementation, application and testing of this model are reviewed.