[dipl] Perustieteiden korkeakoulu / SCI

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Analysis and Modeling for Predicting Icing Losses in Finnish Wind Power Production
(2022-08-23) Uusitalo, Helmi
Perustieteiden korkeakoulu | Master's thesis
Atmospheric icing is a phenomenon in which ice is formed to the surface from the liquid water in the air in cold temperatures. It is a relevant phenomenon in wind power since icing causes challenges with wind turbine materials, maintenance and production estimates, for example. In this work, a new prediction model for icing in wind power production was created, using wind measurement data from three Finnish wind farms and data of weather and atmospheric conditions. The used data include measured power production of the turbines and hourly data of wind speed, temperature, relative humidity, air density, cloudiness and precipitation. From the data, 121 icing events were found from 3 sites during three winters in 2019−2022, using measured production and estimated production calculated with wind speed and air density. Icing events were classified to rime ice, glaze and wet snow events and the differences were found between the icing types. It was found that weather conditions like precipitation and sunshine affect an icing event, and an event is usually stopped by the start of rain or a decrease in cloudiness. In glaze events, where the production is stopped by icing, the ice breakage point could be predicted well with cloudiness and precipitation data. This correlation was one of most important findings in this work, due to high and unpredictable icing losses during glaze events. A new prediction model was created using previous research of ice accretion rate and ice shedding, and the findings from data analysis. The ice accretion and ice shedding coefficients, icing type assumptions and weather data limits were determined to all three sites to optimize the prediction model. It was found that the prediction model could improve the power estimations significantly especially with rime ice and glaze events. The mean squared errors of measured and estimated production decreased by 21% in site 1, 27% in site 2, and 15% in site 3, compared to power estimations without the production model. The model could still be further improved by improving the icing type recognition, but the results of the icing loss predictions were promising.
Application of McSLAP for SLMCPR calculation at Olkiluoto nuclear power plant
(2023-05-16) Kilpeläinen, Joel
Perustieteiden korkeakoulu | Master's thesis
Teollisuuden Voima Oyj (TVO) has procured a copy of McSLAP computer program for probabilistic dryout analysis. In this thesis, TVO-specific thermal hydraulic calculation parameters for McSLAP are calculated for reactor units 1 and 2, while the methodology to take channel bow into account in McSLAP calculations at TVO is developed and applied for calculation of burnup-dependent safety limit minimum critical power ratios (SLMCPR). The effect of channel bow on SLMCPR is studied, and a sensitivity analysis of the thermal hydraulic calculation parameters is undertaken. The results calculated with McSLAP are not sensitive to the TVO-specific thermal hydraulic calculation parameters in a significant manner. The effect of channel bow can cause a variation of an order of 0.02 to SLMCPR if a fuel assembly channel made of Zircaloy-2 is used. A change of this magnitude doubles the fraction of fuel rods experiencing dryout during limiting transient conditions. The bow characteristics of a channel made of Zirlo yield insignificant variation to SLMCPR. Still, channel bow should be accounted for in the SLMCPR analysis in the future and additional channel bow data should be gathered from the power plant units to improve the accuracy of the analyses.
Calculating spent nuclear fuel composition for secondary nuclear safety analyses using nodal diffusion neutronics
(2023-03-21) Kähkönen, Topias
Perustieteiden korkeakoulu | Master's thesis
Various tasks in nuclear engineering require a detailed description of nuclear fuel composition such as simulating the operation of a nuclear reactor, radiation shielding, and criticality safety. Monte Carlo-based transport code Serpent has been routinely used to calculate the depletion of nuclear fuel with high fidelity. However, the Monte Carlo approach for large depletion systems can be computationally demanding. In practice, lower fidelity nodal methods are used to calculate full-core fuel cycle simulations. Ants is a nodal diffusion program used for fullcore neutronics calculations in VTT's Kraken reactor simulator framework. It can model detailed nuclide transmutation chains with a newly implemented microscopic depletion model. A recent study tested the method in structural material activation of a nuclear fuel assembly and this thesis is the first study applying it to fuel depletion. The objective of this thesis is to study if Ants can be used to calculate the nuclide composition of irradiated nuclear fuel. Furthermore, the second objective is to show that Ants-based spent fuel composition can be utilized in a consequent Serpent calculation for secondary nuclear safety analyses. Fuel depletion with the microscopic depletion model was verified in a two-dimensional single-assembly burnup calculation. In addition, a two-year fuel cycle of a three-dimensional small pressurized water reactor core was simulated as a realistic use-case test. Comparisons to higher fidelity Serpent results show that Ants can accurately predict fuel nuclide inventory on the assembly level. However, the method cannot calculate pin-level nuclide distributions which may lead to significant errors in the secondary analysis phase. The micro-depletion capability in Ants is a major addition to the Kraken reactor simulator framework but further work is required for developing it beyond a proof-of-concept stage.
Combined stochastic and nested temporal structure for optimization based planning of energy systems
(2024-09-12) Tupala, Arttu
School of Science | Master's thesis
Including the uncertainty to modelling of energy systems with long-term storage can increase the time it takes to solve a model even by orders of magnitude. While methods exist to address the issue, they either lack the accuracy or do not reduce the solution time enough. In this thesis, a nested structure is presented to reduce the model solution time while keeping accuracy of the results on an acceptable level. It solves the long-term stochastic storage behaviour separately, by introducing a storage model where the same system is solved with coarser data and longer forecasts. This then gives constraints for the storage usage to the short-term stochastic dispatch model. The method was tested with a Denmark-Norway model using historical data to construct stochastic timelines. The comparisons were made between several variations of the nested structure to see which performs the best. Faster solutions with acceptable result quality were achieved both when lowering the temporal resolution of the storage model and separating the long-term water inflow and the short-term wind forecasts to different model instances. Additionally, the nested structure was compared with a basic rolling horizon method. The nested structure resulted in significantly lower costs when the solution times were set to be the same.
Commercial system-level solar photovoltaic test facilities in Nordic conditions - Current status and suggestions for future
(2024-08-20) Markkanen, Magnus
Perustieteiden korkeakoulu | Master's thesis
The share of renewable energy in the global energy production profile has been increasing rapidly thanks to global effort to decrease greenhouse gas emissions. Solar photovoltaics (PV) represents a rather small portion of the renewable energy mix. However, due to the constantly decreasing solar cell prices and improvements in technology, the share of PV is expected to increase quickly in the near future. As the solar PV becomes feasible in new locations, it is crucial to minimize the uncertainty related to the energy yield assessments of these projects. By having more accurate information about the energy yield of new PV technologies, more accurate investment decisions are possible to be made. The objective of this thesis is to determine the current status of solar PV test facilities in the Nordics and formulate a suggestion for a PV test facility that would bring added value to a commercial company acting in the energy sector. The research is performed in three stages. The initial stage is to conduct a literature review of the current best practices and existing approaches. The second stage is to conduct a benchmark study about the existing solar PV test facilities, with a focus on Nordic assets. The third stage of the research is an interview round with professionals from the industry about pressing issues and open questions related to solar PV projects. Finally, a suggestion for potential test facility is formulated based on the previous stages. Based on the literature review and benchmark study, two levels of solar PV testing are determined, module-level and system-level. The module-level testing is more relevant to research organizations and module manufacturers while the system-level testing is typically related to energy yield measurements and in general more beneficial for energy producers. In the benchmark study and the interview round, 13 potential test topics are recognized and evaluated. Topics related to bifacial PV modules and artificial increase of the ground albedo are evaluated thoroughly. A suggestion for test facility is formulated for these two topics.
ERO2.0 modelling of divertor marker erosion in ASDEX Upgrade L-mode experiments
(2024-11-18) Saari, Samuli
School of Science | Master's thesis
Erosion of the inner wall of tokamaks due to sputtering can degrade the plasma performance and increase the maintenance need of the reactor. In this Master’s Thesis, erosion of the divertor surfaces in an experiment conducted at the ASDEX Upgrade (AUG) tokamak has been modelled using the ERO2.0 code for which the necessary sputtering and reflection data was produced using the SDTrimSP code. The results were compared to the previously published experimental data and the validity of the applied assumptions was assessed by varying the simulation parameters. In the experiment, gold markers of two sizes were used as distinguishable proxies for the tungsten wall components and placed in the vicinity of the outer strike point during L-mode plasma discharges in AUG. The larger 5 × 5 mm2 markers were expected to represent the net erosion, as the majority of the eroded particles are re-deposited back to the marker surfaces, while the smaller 1 × 1 mm2 represented gross erosion as particles are expected to be re deposited outside the marker surfaces. For the ERO2.0 simulations in this Thesis, a new background plasma, a new simulation surface configuration, and new energy and angular dependencies for sputtering and reflection data between gold and other particle species were generated to provide improved correspondence to the experimental conditions and more accurate interpretation of the erosion of the gold markers. The revised simulation configuration — particularly the new sputtering data — was found to provide a nearly perfect match to the experimentally determined net erosion rate of the larger marker surfaces. The results for the smaller markers agree with the experimental data in the scrape-off layer, whereas deviations were observed in the private flux region and the vicinity of the strike point. Erosion of gold was caused mainly by background plasma impurities. In comparison to toroidally uniform tungsten surfaces, the simulations suggested that the gold markers overestimated the net erosion of tungsten by a factor of 15–20 due to the generally higher erosion yield of gold and incomplete representation of its re-deposition on the small marker surfaces.
Estimation of ITER FILD fast ion fluxes using ASCOT simulations
(2023-08-22) Hyvärinen, Otso Juhani
Perustieteiden korkeakoulu | Master's thesis
One of the main goals of the ITER project is to reach Q = 10 operation. At these conditions, alpha particles will be the dominant source of plasma heating. Therefore, it is essential to understand how well these particles are confined. The fast ion loss detector (FILD) will be installed to test new models for the fast alpha particle losses. The objective of this thesis is to show that the ITER FILD is expected to measure fusion-born alpha particle fluxes larger than the background noise in Ip = 15 MA H-mode baseline. Furthermore, the effect of the neutral beam injector (NBI) heated deuterium ions on the FILD signal was studied. Velocity-integrated pinhole fluxes were analyzed from the ASCOT simulation with two different schemes. A uniform flux approximation resulted in a signal strength two orders of magnitude larger than the threshold for fusion-born alpha particles. A more accurate estimation method, voxel sum estimate, resulted in three orders of magnitude larger estimated pinhole flux compared to the threshold for fusion-born alpha particles. For NBI deuterium ions, the voxel sum estimate gave a factor of 500 larger than the threshold deuterium ion flux. However, neither of estimates include analysis of the velocity-space distribution of the incoming particle flux, so the estimations of only pinhole fluxes exceed the observable signals from the scintillator plate corresponding to the pinhole fluxes. The velocity-space of the incoming fluxes response on the scintillator plate was analyzed with the FILDSIM code. The results show that, when NBI is turned on, low-energy response (gyroradius < 6 cm) is dominated by the NBI, and fusion-born alpha particle response cannot be identified. However, higher energy response is caused by only fusion-born alpha particles, and low-energy response is observed if NBI is turned off. The magnitude of the peak fusion-born alpha particle response from the scintillator plate indicated that signal from fusion-born alpha particles is observable as low as 4% of the nominal fusion power.
Fabrication and characterization of metal supports for metal-supported solid oxide fuel cells
(2024-03-12) Savikko, Axel
Perustieteiden korkeakoulu | Master's thesis
The pressing issue of anthropogenic climate change calls for new innovations in renewable energy technologies to further decrease the use of fossil fuels. Solid oxide cells, both fuel cells and electrolysis cells, are a technology that are efficiently able to utilize hydrogen to produce electricity in fuel cell mode and produce green hydrogen using electricity in electrolysis mode. Green hydrogen can be used in a lot of industries to decrease the amount of fossil fuels used. These include e.g. the fertilizer and steel industries. However, solid oxide cells are not commercialized at a large scale, the largest issue being the cost to fabricate them. Metal-supported solid oxide fuel cells are a concept, where most of the expensive fuel cell materials are replaced by a cheap stainless steel material. This lowers the cost of the materials, and provides other benefits such as good electric conduction and thermal properties. The metal also comes with some drawbacks, such as corrosion and chromium diffusion. Further research into this topic might solve these issues, resulting in a cheap and effective metal-supported solid oxide fuel cell. In this thesis, a metal support made out of a super-duplex stainless steel is fabricated and characterized. The supports were fabricated using differing sintering profiles, where both the temperature and time of sintering were changed. The compatibility to fuel cell materials, electric resistance, porosity and mechanical strength of the supports were measured to determine the viability of the metal for use in metal-supported solid oxide fuel cells. Scanning electron microscopy was then used to further understand how the microstructure of the supports change based on the sintering profiles. The best support was sintered at 900 °C for 2 h with an area-specific resistance of 1 Ωcm2 flexural strength of 6 MPa and porosity of 55 %.
Forecasting of Zonal Power Transfer Distribution Factors in Flow-Based Market Coupling
(2023-12-12) Andersson, Mika
Perustieteiden korkeakoulu | Master's thesis
This thesis focuses on forecasting the Zonal Power Transfer Distribution Factor (PTDF) in the context of Flow-Based Market Coupling (FBMC). The growing share of renewable energy in European energy sector has brought challenges to electricity markets and accurate forecasting of price. The FBMC methodology was introduced to address the challenges of renewable dominated energy system, but little research has been conducted on predicting Flow-Based (FB) parameters. The thesis develops a model based on the physical characteristics of nodal PTDF and Generation Shift Keys (GSKs) to forecast zonal PTDF values. The nodal PTDF represents the sensitivity of power flows in critical network elements (CNEs) during a power transfer between different nodes, while GSKs capture the relationship between zonal power transfers and nodal power injections. The model is built on the perspective of a market participant and therefore, only utilizes publicly available data. The model's effectiveness is tested using historical data from the External Parallel Run (EPR) of the capacity calculation by the Nordic Regional Coordination Centre (CCR). The results are reasonably accurate, with generally small errors in the predicted PTDF values. Suggestions for improving the model focus on the functioning of the metric used for the forecasted values. Additionally, the thesis adds to the current research on the theory and behaviour of the FBMC parameters in changing electrical systems.
Landau-Zener driven 02-transition in a transmon circuit
(2022-12-13) Björkman, Isak
Perustieteiden korkeakoulu | Master's thesis
In recent decades, a lot of effort has been seen to realize and control a large-scale quantum computer. Among the most promising architectures for such a system is that of superconducting circuits. However, a significant challenge with these qubits is the drifts in system parameters. Therefore, controlling thousands or more qubits - which are needed to perform practical applications - becomes increasingly difficult and various control schemes and workarounds are needed to vanquish such obstacles. One approach to cope with the complexity of the system size is to increase the information held per quantum system by introducing an additional state and thereby reduce the number of qubits. Therefore, in this work, we explore a robust population transfer, from the ground to the second excited state, on the first three levels of a superconducting transmon. For a transmon, such a transition cannot occur by single photon absorption. However, because of a second-order process, two-photon transitions from the ground state to the second excited state are possible for a drive at the 02-transition frequency. In existing protocols that drive this population transfer, such as the Raman process and (sa)STIRAP, a common problem is the sensitivity to offsets in frequency and amplitude of the drive pulses. Therefore, in search of a method that realizes such a transfer and is robust to some offsets we took inspiration from \cite{Mppr} and approached the problem through a Landau-Zener process. The Landau-Zener process in this work was a result of modulating the frequency of a one-tone drive around the 02-transition frequency that interchanged the first and third energy levels while avoiding the intermediate level. With this method, the three-level quantum system (approximately) follows the first eigenstate of the Hamiltonian adiabatically to the second excited state. This method showed considerable robustness to both offsets in frequency and amplitude and was eventually tested experimentally on a superconducting transmon. The results showed great agreement with the theory and demonstrates a method that is robust and simple enough to be realized on the majority of control hardware.
Locating and predicting Internal Reconnection Events in ST40
(2024-06-19) Niemelä, Anna
Perustieteiden korkeakoulu | Master's thesis
In response to the critical need for sustainable energy sources, fusion energy has emerged as a promising solution. Spherical Tokamaks, with their compact design and cost-effectiveness, have garnered attention for their potential in fusion research. However, challenges unique to Spherical Tokamaks, such as Internal Reconnection Events (IREs), pose obstacles to achieving stable fusion reactions. This study focuses on analyzing, locating, and predicting IREs using data from the 40 cm major radius spherical tokamak ST40, operated by Tokamak Energy in the UK. By automating the detection and location of IREs, the aim is to create a dataset for machine learning approaches, utilizing data from several different plasma parameters and control currents. Through this analysis, we seek to identify key factors for identifying IREs and develop predictive models to anticipate their occurrence. Three different approaches were tested, including two different Multilayer Perceptron (MLP) models (a binary approach and a regression approach) and a Long Short-Term Memory (LSTM) model. The best regression MLP model yielded a coefficient of determination of 0.82 on average and correctly predicted 96 percent of the operational pulses with and without an IRE. The LSTM model achieved a slightly lower coefficient of determination, but similar accuracies in predicting IREs. Based on the results of the modeling, plasma parameters and control current values can be used to detect IREs beforehand. An alarm system could potentially be implemented to detect IREs by using parameters that can be derived in real-time as input features. Models based on the methods used in this project could then contribute to the development of monitoring and control systems for avoiding IREs.
Manufacturing and Characterization of Epoxy Based Flexible Thermoelectric Modules
(2023-05-16) Zhang, Quanzeng
Perustieteiden korkeakoulu | Master's thesis
Thermoelectric module can convert waste heat into electricity due to its unique Seebeck effect. Since a great deal of heat produced in households and factories has been wasted. It is significant to collect the waste heat by thermoelectric modules. However, conventional thermoelectric modules mainly possess rigid substrates, which limits their applications in complex situations, such as the industrial pipe and human body. Thermoelectric modules with flexible substrates can overcome this drawback. Flexible thermoelectric module can be bent to adapt to uneven surfaces. Hence, it requires superior mechanical strength in order not to break when bent. The mechanical strength highly relies on the binding material. Binding materials can be classified into solder paste and electrically conductive adhesive. This work presents a new electrically conductive adhesive named 2D-ECA, synthesized by RISE (Research Institutes of Sweden) and Linköping University. Various characterization methods have been applied to study its performance in the device. In this work, we mainly focused on the mechanical strength, electric conductivity and thermoelectric property of 2D-ECA. We found that the mechanical strength of 2D-ECA is as high as superior commercial solder paste and electrically conductive adhesive. What’s more, 2D-ECA will not damage the inherent mechanical strength of the thermoelectric leg as the solder paste. However, the electric resistance of 2D-ECA based samples is considerably higher than solder pastes. As a result, devices fabricated with 2D-ECA showed a relatively lower output power. Hence, further research should focus on improving the electrical conductivity of 2D-ECA. Nevertheless, further study illustrated that 2D-ECA can be used on aluminium substrate, while it is impossible for ordinary solder pastes. It is a significant step towards low-cost devices.
Numerical study on hydrogen flame instabilities in 2D using thickened flame approach
(2024-01-23) Rintanen, Aleksi
Perustieteiden korkeakoulu | Master's thesis
Premixed lean hydrogen flames are thermodiffusively unstable, which causes the flame front to wrinkle considerably without any effect of turbulence, causing the flame to propagate much faster compared to that of the laminar unstrecthed burning velocity. Hydrogen flames are also very thin interfaces, which makes the modeling of the flames challenging, since in practical computational fluid dynamics (CFD) simulations it is not possible to solve such small length scales accurately. The artificial thickened flame model targets at manipulation of the governing equations so that the flame front is artificially thickened without affecting other characteristics of the flame allowing the use of a coarser grid. This master's thesis studies the effects of artificial flame thickening on intrinsic flame instabilities. An open source C++ CFD toolbox OpenFOAM is used for the simulations, where the dynamic variant of the thickened flame model is implemented. The results show that the use of the thickened flame model will affect the length and time scales of intrinsic flame instabilities. The thickened flame model can be derived as a coordinate transformation, where space and time are stretched with the thickening factor locally inside the flame front. Numerically calculated dispersion relations remain invariant under the transformation if the dispersion relation is normalized with the laminar flame thickness and the flame time of the thickened flame. This means that thickened flame model scales the response to harmonic perturbations towards longer wavelengths while damping the growth rate by the thickening factor. Statistically similar intrinsic instabilities are obtained when the thickened flame model is used, but the length and time scales of the instabilities are stretched by the thickening factor. This leads to slower developments of the flame fingers and thus, slower consumption speeds during the flame front development, compared to the DNS results, while the final consumption speeds remain approximately the same.
Probabilistic Risk Assessment Modeling for Multi-Module Small Modular Reactors
(2024-11-18) Cederlöf, Nina
School of Science | Master's thesis
Small modular reactors (SMRs) have gained global interest due to the demand for carbon-neutral energy. However, their new technologies, such as passive systems and modular design, may challenge current nuclear safety regulations and analyses. Current safety analysis methodologies focus on individual units with few dependencies, whereas SMR modules may have several dependencies, necessitating integrated modeling that accounts for interactions between multiple modules within a single model. This thesis focuses on modeling multiple SMR modules by creating a multi-module modeling logic with probabilistic risk analysis (PRA) tools. The logic aims to model accident sequences involving multiple modules. A literature review identified three modeling methodologies for traditional multi-unit sites: the master event tree (MET), single-top fault tree (SFT), and a hybrid of the two. Additionally, one SMR-specific modeling approach was found. The approach applies basic event (BE) and initiating event (IE) parametric adjustments to single-module models. The goal of the thesis is to study how well the three PRA methodologies, originally developed for sites with multiple traditional units, fit for modeling a plant with multiple SMR modules. The BE and IE parametric adjustment approach is not as explicit as the three other modeling approaches. However, the approach could be potentially used in the graded approach, which involves assessing the safety significance of different events by considering the varying levels of risk associated with different modules and their interactions and then allocating the resources to the most risk-significant issues. The thesis demonstrates that all three approaches, MET, SFT and the hybrid, can be applied in multi-module modeling. Analysis of the approaches revealed that each approach has distinct advantages and limitations in multi-module PRA modeling. In this thesis, the efficiency of the modeling process, scalability of the models and the readability of the resulting models are considered. The hybrid and SFT approaches seem to have a great potential with modeling multiple modules in PRA. The two enable efficient modeling and good scalability. The hybrid approach may offer slightly greater efficiency and scalability. However, the two do not visualize the accident sequences in a very user-friendly way. MET, on the other hand, illustrates accident sequences very clearly. The problem is that the size of the MET grows rapidly when more modules are modeled, and a larger model may be extremely difficult to read.
Spatial filtering of optical fields using nonlocal non-Hermitian metasurfaces
(2024-08-20) Reichler, Mikael
Perustieteiden korkeakoulu | Master's thesis
Spatial filtering of light is ubiquitous in optical systems, but it can be challenging when considering the growing demand for miniaturization of these systems. In this thesis, we develop metasurface-based spatial filters that, unlike conventional spatial filters, can be made ultrathin and robust against displacements with respect to the optical beam. By designing the eigenmodes of the nonlocal metasurfaces to form a non-Hermitian system, we aim to increase the spatial selectivity of our filters beyond that obtainable with other photonic structures. We design the metasurfaces to be nonlocal by constructing them from a waveguide grating that supports spatially extended propagating modes, while constraining the geometric parameters to ensure fabricability of the structure. The dispersion relation of the propagating modes is optimized computationally to achieve a non-Hermitian band structure. The filtering properties of the metasurfaces are then further improved by defining and maximizing a Figure of Merit that quantifies the required low-pass filtering performance. Finally, the metasurfaces are combined into compact spatial filtering devices and their properties are studied using the methods of Fourier optics. As a result, we demonstrate a planar, transmissive low-pass spatial filter that comprises a half-wave plate sandwiched between two metasurfaces, achieving a semi-circular peak transmission window at normal incidence with a width of 1 degree and the peak transmittance reaching 0.7, while the average transmittance for spatial components with incidence angles between 1 and 10 degrees is below 0.008. In addition, a spatial high-pass filter based on a similar construction is presented. These computational results add to the existing base of non-Hermitian photonic devices and motivate further research in metasurface-based spatial filters.
Systematic investigation of ceramic composite electrolytes consisting of proton and oxide-ion conductors for fuel cell and electrolyzer applications
(2023-08-22) Virtanen, Sini
Perustieteiden korkeakoulu | Master's thesis
Extreme concern over the depletion of fossil fuel resources and increasing of greenhouse gas emissions has led to significant research into clean and sustainable energy production. Fuel cells are electrochemical devices that enable the conversion of chemical energy directly into electricity when fuel is supplied, producing clean energy. Thus, fuel cells have attracted growing interest in recent years among various alternative energy technologies. According to the electrolyte used, solid oxide fuel cells (SOFCs) are classified into oxygen ion-conducting SOFCs and proton-conducting SOFCs. In this thesis, we investigate proton-conducting electrolytes BZCY and BZCYYb, and ion-conducting electrolyte GDC as a reference material, with and without an addition of carbonates. Electrochemical measurements are done to get a better knowledge about the proton-conducting method and compare the proton-conducting materials to the more common ion-conducting material. Electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and scanning electron microscopy (SEM) are performed on electrolyte pellets fabricated by pressing method. The total conductivities and activation energies of the electrolyte pellets are investigated with electrochemical measurements. In addition, the topography of the surface is studied from the SEM results. The BZCYYb + NLK electrolyte pellet under H2 achieved the best conductivity, 0.40 S/cm at 600°C. The lowest activation energy 0.179 eV is reached with BZCY + NLK electrolyte pellet in an atmosphere of H2. We observed that the proton-conducting electrolyte pellets with carbonates have significant enhancement in performance and are better electrolytes compared to the other samples according to EIS and CV measurements.
Temperature Dependence of Valve Stem Packing Emission Performance
(2024-08-20) Hyvärinen, Riku
Perustieteiden korkeakoulu | Master's thesis
Increasing awareness of harmful effects of industrial emissions has led to constantly tightening regulations aiming to reduce emissions in all fields of industry. A part of industrial emissions are fugitive emissions, which are uncontrolled leaks of pollutants from pressurized vessels, pipelines and valves. In the process industry, valves are the most significant source of fugitive emissions, mostly caused by the dynamic stem sealing. Decreasing accepted leak rates create challenges for stem sealing solutions, especially at high temperatures. This thesis focuses on the emission performance of a gland packing, which is a typical valve stem sealing solution. In a gland packing, sealing is based on packing rings made of porous and elastic materials, compressed in a packing cavity. Leak is dependent on many factors, such as packing stress and stem surface quality, and it can occur as a surface leak at sealing interfaces and through the porous packing material. In this work, packing rings made of braided graphite are used in rotary valve applications. The most essential part of this work is experimental testing. Packing ring compression tests were carried out to determine the viscoelastic properties of a packing material as a function of temperature and time. In addition, leak testing was done in special test rigs to measure leak rates trough the stem sealing in different temperatures. In leak testing, standardized test cycles were used as well as custom test cycles planned specifically for the determination of the temperature dependence of leak rate. In addition to experimental testing, numerical simulations of packing behavior were performed to obtain information about packing stress distribution as a function of temperature to help understanding the leak mechanisms. A temperature-dependent material model was calibrated based on the experimental data from the packing compression tests. Several packing configurations were subjected to finite element analysis in different conditions. Finally, simulation results are compared to experimental test results to assess the functionality of the material model.
Two dimensional combustion jet
(2024-08-20) Malinen, Jesse
Perustieteiden korkeakoulu | Master's thesis
This thesis presents an OpenFOAM simulation of a combustion jet stream. The calculation problem is an assignment from a fuel cell system manufacturer Convion as a way of evaluating OpenFOAM as a tool for developing fuel cell system burner. The work is conducted by simulating the combustion jet with OpenFOAM and by conducting analytic analysis on a zero dimensional combustion reactor. The analytic formulations are shown explicitly and the case set up in OpenFOAM is discussed. The results include discussion compering the analytic and simulation results. The OpenFOAM simulation is conducted as a two dimensional jet stream with parallel flowing oxidizer and fuel streams. Heat transfer inside the domain is included in the simulation. The flow is simulated with a turbulent k-𝜔SST-model, which is a Reynolds Averaged Navier-Stokes -model. Reaction mechanism used is a reduced GRI-MECH 1.2. mechanism, which includes 21 reacting species and 84 chemical reactions. Combustion analysis includes different reacting species, so all the analysis is conducted as multi-component mixtures. The analytic formulations include equilibrium composition of the combustion gases, adiabatic flame temperature, laminar flame speed and reaction kinetics. Cantera is utilized in the laminar flame speed calculations. Heat capacities of the species are obtained from Janaf polynomials, and dynamic viscosities and thermal conductivities are calculated based on rigid collision theory. Also heat transfer and flow properties are estimated. Experiences gathered during the work show that OpenFOAM is a usable tool in combustion analysis. The results also emphasize the spatial dependence of reacting flows, since the zero dimensional results do not directly correspond to the simulation results. Some resemblance can be seen for example with the adiabatic flame temperatures, but the spatial dimensions introduce losses, so ideal solutions do not exactly apply. At the end, the design of the jet geometry wasn’t sufficient for comparing the equilibrium calculations with the simulation results.
UEDGE predictions of SOL flows in DIII-D lower single-null L-mode plasma
(2024-01-23) Myllynen, Luukas
Perustieteiden korkeakoulu | Master's thesis
The deuteron and C2+ ion flows in the scrape-off layer are studied and compared for low confinement mode plasmas in the lower single-null geometry of the DIII-D tokamak using the multi-fluid edge-plasma code UEDGE. The factors driving the flows and locations of stagnation points as well as the degree of impurity entrainment and impact of deuterium molecules are assessed. The simulations are performed with and without electromagnetic drifts and currents for forward and reversed toroidal magnetic field configurations. UEDGE predicts that the magnitude and distribution of radial flows across the separatrix driven by diffusion, convection and cross-field drifts dominate the scrape-off layer flows. While the ionization fronts in the high-field side (HFS) and low-field side (LFS) divertors move from the targets toward the X-point as the LFS midplane densities increase, parallel-B flows in the HFS and LFS divertors increase toward their respective target plates. This result indicates that in the configuration considered in this work, the opposing pressure gradient force caused by the ionization front is outweighed by the impact of other parallel-B forces. The predictions show that the drift configuration affects the distribution of the radial fluxes across the separatrix, recycling fluxes, and ionization rates, which impact the scrape-off layer flows and determine the locations of the stagnation points. Without drifts the stagnation points are located near the LFS midplane. In the forward toroidal field configuration the B × ∇B drift directed toward the divertor drives the stagnation points closer to the LFS target. In the reversed toroidal field configuration the B × ∇B drift is directed to the opposite direction shifting the stagnation points to the top of the plasma. The simulations show that the entrainment of C2+ ions in the deuteron flow increases in the divertor, toward the outer wall, and with the LFS midplane electron density, as predicted by theory, which states that the entrainment is strongest in cold and dense plasmas. The results suggest that coherent imaging spectroscopy, which measures C2+ flows, can be used to determine deuteron flows in the divertor with 30-100% accuracy and near the outer wall with 80-100% accuracy. Furthermore, the predictions demonstrate that the disagreement between simulations with and without deuterium molecules increases with density due to the increasing number of molecules, and that the presence of molecules causes the plasma to detach at a 5 · 10^18 m−3 lower LFS midplane electron density.
Ultrasonic anemometry in rain
(2024-03-11) Kavanagh, Benjamin
Perustieteiden korkeakoulu | Master's thesis
This work aims to identify the issues related to low power ultrasonic anemometry in rain. To begin, the operating principles of ultrasonic anemometers are introduced to the reader with a focus on the time of flight method. The factors that the measurement depends upon are discussed along with the affects of rain on the measurement. The standardisation landscape for anemometer performance in rain is scoped. A range of ultrasonic anemometers were tested at varying wind speeds in rain under laboratory conditions. The performance of each is assessed against operation in dry conditions and the presence of water on transducers is observed to be most detrimental. Finally, mechanical features designed to mitigate the affect of water are evaluated and design considerations are provided.

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Browsing [dipl] Perustieteiden korkeakoulu / SCI by Degree programme/Major subject "Advanced Energy Technologies"