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Senast publicerade
- Evaluation of Candidate Materials for Chemical Looping Combustion Fuel Reactor Superheaters(2026) Fredriksson, Nils; Mitrovic, IgorChemical looping combustion (CLC) is a promising technology, enabling effective carbon capture and storage while reducing the energy penalty associated with car bon capture and storage in conventional waste-to-energy systems. The fuel reactor (FR) side of a waste-fired CLC system exhibits a harsh oxidizing environment; conse quently, the material selection is essential for achieving reliable long term operation. This thesis has evaluated the corrosion resistance of six candidate superheater ma terials for use in the FR of a CLC system. The investigated alloys were Sanicro 28, Sanicro 35, Sanicro 60, TP347, EF101, and a low-alloyed reference steel T22, also used for method development. The samples were exposed for 168 hours at 400◦C in an atmosphere containing 5% O2, 20% H2O and CO2 bal. Potassium chloride was deposited on the sample surfaces to simulate the alkali chloride-containing en vironment associated with the combustion of waste-derived fuels. Using gravimetric analysis combined with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) the corrosion behavior was analyzed. Results show that Sanicro 28, 35, and 60 exhibit the lowest mass gains and formed thin protective scales with no visible sign of internal oxidation. TP347 also demon strated good corrosion resistance, although evidence of internal oxidation was ob served. EF101 experienced breakaway corrosion along with T22 although spalla tion was not observed to the same degree. Cross-sectional analysis showed that the Ni-containing alloys were able to form a thin and protective oxide scale which is likely composed of a chromium-rich oxide, while EF101 failed to establish and maintain a continuous protective Al-rich oxide scale, resulting in the formation of Fe- and Cr-rich corrosion products. Chlorine enrichment within the oxide scales also suggest that chlorine induced degradation through the electrochemical mechanism contributed to higher degradation of the metals. The results indicate that all Sanicro samples along with TP347 are viable candi date materials for use in superheaters in CLC systems. Considering both corrosion performance and alloy composition, TP347 emerges as the most economical alter native due to its lower Ni content, providing a significant improvement in corrosion resistance compared to T22.
- At the Heat-Pipe Limit – Coupled Modelling and Operating-Limit Assessment of a Heat-Pipe-Cooled Microreactor(2026) Andersson, Karl; Persson, FelixHeat pipes are efficient transporters of heat and are currently being considered in new microreactor designs. To support efforts in understanding the behaviour and limitations associated with using heat pipes as primary heat removal components in microreactors, a reduced coupled model of a fuel assembly is developed in this thesis. The model is based on publicly available information on the Westinghouse eVinci reactor, a prominent design currently under development. The reduced model functions as an effective one-fuel-pin–one-heat-pipe model of a fuel assembly in an eVinci-like reactor and couples one-dimensional neutronics, two-dimensional heat transfer, and one-dimensional fluid flow. Applying the model to an estimated reactor configuration suggests that an eVinci-like reactor operating at the marketed power output is within the heat-pipe limits considered in this thesis. The results also indicate that the model complexity can be further reduced in normal operating conditions, and partly in limiting conditions. Fixed-temperature approximations for the neutronic data and the thermal conductivities have a small effect on the neutronic effective multiplication factor, and do not alter the temperature and neutronflux distributions significantly. Furthermore, approximating the heat-pipe vapour as isothermal is acceptable under normal operating conditions, but breaks down near the sonic limit.
- Classical ghosts - A literature study of the Batalin-Vilkovisky formalismAndersson, LeoGauge symmetry appears in many physical theories and is often handled by just imposing gauge choices, i.e. removing the gauge symmetry as it consists of unphysical degrees of freedom. This approach may fail when symmetries do not close on-shell and obscures underlying structure of the theory. The Batalin-Vilkovisky formalism describes the connected structure of (higher) gauge symmetries, their corresponding (higher) Noether identities and equations of motion, by introducing a plethora of extra fields called ghosts, antifields and antighosts to represent these. This literature study starts with the introduction of graded structures, from graded vector spaces to Q-manifolds and their duals L∞-algebras, whereafter the physical phenomena and problems that motivates the BV formalism are explained. These phenomena and the formalism itself are then formulated in terms of the introduced mathematical framework. The extra fields are regarded as elements or sections of a symplectic Q-manifold. Central for the BV formalism is an action S that through the symplectic structure induces a differential which in turn gives the equations of motion, gauge transformation etc. when it acts upon the corresponding field. In the L∞-dual description the gauge symmetries etc. are formulated in terms of higher products that generalise the Lie bracket, while equivalence between physical theories corresponds to quasi-isomorphisms. After some minor examples and calculations the thesis ends by revisiting a BV formulation of 10D supersymmetric Yang-Mills, with the help of bosonic spinors and weight partition functions.
- Investigation of the influence of coating and drying methods of catalytic inks on the structure of resulting electrodes for Proton Exchange Membrane Fuel Cells(2024) Nair, Sandeep JayaprakashIn the decal transfer process of making catalyst electrode coatings for Proton Exchange Membrane Fuel Cells (PEMFCs), understanding the coating and drying parts of the process is important to get desired final electrode structures. Coating and drying are also important manufacturing steps and must be optimized for this as well. The structural evolution during drying from ink microstructure to the electrode microstructure yields the resulting pore structure at a micro scale, and at a larger length scale the crack morphology. To achieve the desired structures, we need to make both a well dispersed catalyst ink with good interaction of components and provide favorable drying conditions. In this study, different solvent combinations and dry weights in ink, and different drying conditions of temperature and vapor pressures were explored. Qualitative inspection of digital microscope images of the electrodes was used to analyze dried structure and cracks. Critical Crack Thickness (CCT), the height up to which a coating can inhibit cracks well, and the maximum catalyst loading in each setting was monitored. Results showed that 1-propanol rich solvent matrix with water gave the least cracks and highest CCTs in comparison to ethanol and tert-butanol for the studied catalyst and ionomer. Higher temperatures did not have a strong impact on crack morphology or CCT for the same ink recipes but reduced the drying time. Higher vapor pressure of alcohol above the wet ink coating led to slower drying and enabled higher CCTs. The experiments enabled us to achieve coatings with a loading of 0.7 mg/cm2 and a CCT of 250 microns, robust to higher temperature drying conditions, which was not possible before with recipes described by suppliers. The results here are promising for making high performance electrodes in-house and has set a foundation for future work on fuel cells for a variety of applications, helping the green energy transition.
- Cooper Pair Spectroscopy for Odd-Frequency Superconductors(2026) Hermansson, JohanIn conventional spin-singlet superconductors with even parity, the anomalous pairing amplitude is even in frequency. Odd-frequency superconductivity is an unconventional superconducting state in which the pair amplitude is odd under exchange of time coordinates. Since superconducting pairing is encoded in two-particle correlations, double photoelectron spectroscopy provides a natural framework for probing such states through the simultaneous detection of two photoemitted electrons. When applied to superconducting samples, this approach is commonly referred to as Cooper pair spectroscopy. In this thesis, a Green’s-function formulation of Cooper pair spectroscopy for odd-frequency superconductors is developed by extending the theoretical structure of angle-resolved photoemission spectroscopy to the doublephotoemission case. Starting from an expansion of the S-matrix, the double-photoelectron counting rate is derived to second order, which is the lowest order giving a non-vanishing contribution. The result separates into an anomalous contribution, expressed through greater anomalous Green’s functions, and a normal contribution, expressed through lesser normal Green’s functions. The anomalous part describes correlated emission associated with a single Cooper pair, while the normal part describes contributions from ordinary single-particle correlations. The main result is that odd-frequency pairing leads to a different momentum structure in the anomalous contribution than conventional even-frequency pairing. In particular, the odd-frequency kernel contains a difference of screened Coulomb potentials, whereas the even-frequency case contains their sum. Consequently, for a symmetric screened Coulomb potential, the momentum dependence of the electron– photon coupling becomes essential for obtaining a finite odd-frequency anomalous contribution. The derived expression therefore identifies a key formal distinction between even- and odd-frequency superconductors in double photoelectron spectroscopy and provides a basis for future numerical and experimental investigations.