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- Post1D model development and simulation of low-grade waste heat recovery from a marine engine(2021) Bhandari, Varun; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Papadokonstantakis, Stavros; Papadokonstantakis, Stavros; Galuppo, FrancescoThe increasing awareness about the effect of emission of CO2 into the atmosphere, as well as meeting the emission targets set by IMO (International Marine Orga- nization) by 2050 results in a continuous need for improving efficiencies of marine engines. A large portion of the fuel's chemical energy is lost to the surroundings as heat, even in the most energy efficient engines. Waste heat recovery through a rankine cycle has emerged as a promising way to increasing the engine efficiency by utilizing the untapped availability of waste heat in the coolant systems as well as the exhaust of the engine. The highly transient nature of operation of an engine and depicting the heat transfer phenomenon in an ORC (Organic Rankine Cycle) accurately makes the represen- tation of an ORC through a mathematical model quite challenging. Based on the application, selection of the right working uid, equipment and control strategy is crucial for the performance of the ORC In this thesis, a Simulink based mathematical model of an ORC for waste heat recov- ery from a marine engine is built. The WHR (Waste Heat Recovery) model is built for transient operation. The model is run on a road cycle, built from actual field test data of a boat, to simulate its performance in actual operation of the marine vessel. Further, the performance of ORC with di erent working uids and different type of expanders is evaluated. And finally, a rough cost estimation of the ORC is done. The results from the project show that the refrigerant R1234ze(Z) is the most suit- able for engine coolant WHR application and turbine expander performs better than the volumetric expander. Lastly, as the scale of the ORC system increases, it becomes increasingly cost effective.
- Post1D Modelling of Fuel Mixing and(2013) Gustaf, Lindberg; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentA one-dimensional model for fuel mixing and conversion in a bubbling fluidized bed has been developed. The model includes fuel particle size development and calculates the concentration profile for char, volatiles, moisture and ash as well as the fuel particle size distribution. Three different kinds of units have been modelled: gasification, combustion and chemical-looping combustion. Two types of fuels, wood and coal, have been used. Based on the results from the model, the addition of a fragmentation sub-model is very important to fully characterize the char composition in the outlet and the inclusion of particle size classes and particle size development has a large effect on the result. The model presents convergence problems for certain combinations of inputs, such as combustion of fragmenting wood. The model results are sensitive to the value of many inputs such as fuel specific parameters regarding fragmentation and reaction kinetics. Because of these inputs, the use of the model for non-characterized fuels can only be of more qualitative than quantitative use.
- Post20 kW pulslastnätdel - topologival och genomförande(2008) Vinnberg, Andreas; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentDenna rapport visar på skillnaderna mellan både topologival på hög abtraktionsnivå, huvudsakligen energilagring och medel- eller peakenergiöverförning som på låg abstraktionsnivå såsom switchtopologi (flyback, halvbrygga, fullbrygga och så vidare) och likriktning för ett fall med hög lastvariation och algebraiska uttryck formuleras för val av desamma. Funktioner för kondensator- och transistoregenskaper i förhållande till deras pris beräknas och val av optimala kondensator- och transistorval diskuteras. En prototyp byggdes för att verifiera resultaten. För en DC/DC-omvandlare som matas från en PFC med 20 kW medeleffekt under pulslast föreslås en peakeffektomvandlare bestående av två fullbryggor, fasskiftade 180 grader ur fas som har i princip all energilagring på primärsidan.
- Post3-D computations of eddy current losses in core ends of salient-pole synchronous machines(2004) Chitroju, Rathna; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and Environment
- Post3D Radiative Transfer Modeling of the Red Supergiant NML Cyg(2021) Hirvonen, Per; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; De Beck, Elvire; De Beck, Elvire; Andrews, HollyRed supergiants are bright but cool massive stars that have depleted their core hydrogen supply and have started fusing heavier elements. These evolved stars ex perience a strong mass loss through a slow moving stellar wind that results in an extended circumstellar envelope with a rich chemistry. The circumstellar envelopes of red supergiants will eventually enrich the interstellar medium, influencing the formation and evolution of the next generation of stars and planets. Understanding the mass loss of massive evolved stars is a key component in understanding both the evolution of individual stars and the chemical evolution of the universe. We analyze carbon monoxide emission around the red supergiant NML Cyg ob served with the ground based JCMT 15 meter and Onsala 20 meter telescopes, as well as the HIFI instrument aboard the Herschel Space Observatory. The line pro files have complex shapes, suggestive of multiple components in the stellar outflow. 3D radiative transfer modeling is used to recreate the observed line profiles. We con clude that it is possible to recreate the observed line profiles by using one spherical component and three directed outflows.
- PostA 1296 MHz Earth-Moon-Earth Communication System(2015) Lindgren, Magnus; Chalmers tekniska högskola / Institutionen för rymd- och geovetenskap; Chalmers University of Technology / Department of Earth and Space SciencesThe task of designing, building and characterizing an Earth–Moon–Earth (EME) communication system in the 1296 MHz amateur radio band has been successfully accomplished. Using the radar equation and thermal noise theory, in conjunction with measured and estimated system parameters, the lunar echo signal to noise ratio (SNR) has been estimated at 5.4+1.2 −1.6 dB (2) in a 100 Hz bandwidth. The results of empirical long-term averaged SNR measurements are within the boundaries of this estimate, thus adding to its validity. Additionally, measurements of the libration-induced Doppler spread of the lunar echoes show good agreement with theoretical predictions. Further experiments should be conducted however, in order to asses the repeatability of the results. Improvements to the system and measurement methods should also be considered. The report focuses on both theory and practice and apart from the above, additional attention is given to the topic of low noise figure (NF) measurements due to the systemic importance of the LNA NF parameter.
- PostA 3D-model for O2 airglow perturbations induced by gravity waves in the upper mesosphere(2017) Li, Anqi; Chalmers tekniska högskola / Institutionen för rymd- och geovetenskap; Chalmers University of Technology / Department of Earth and Space SciencesTo investigate the influence of atmospheric waves in the mesosphere, a new Swedish satellite MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) will be launched in 2019. It will observe infrared emissions at 762 nm from the O2(b1+ g ) airglow in the region of 70 - 110 km altitude. As a part of the design work for the MATS project, an accurate forward model is needed to estimate what MATS is expected to measure. The results from this model will be used to evaluate the retrieval methods for processing the measurements from MATS. In this thesis project, a gravity wave model and a photochemistry model were coupled to simulate both the day- and nightglow emission fields in three spatial dimensions and time. Simulated satellite images were generated taking into consideration the sphericity of the Earth and the limb-viewing geometry of MATS. Simulation parameters were set according to the preliminary design of the instrument, such as the satellite orbit, image resolution and spectral selections. These satellite images were the first simulated airglow limb images made for the MATS project. By analysing the output data, the relations between wave parameters and airglow perturbations were investigated. It was shown that wave patterns can be easily observed between 85 - 105 km due to the relatively large perturbation in airglow emissions. The O2 airglow emission field was found to be highly sensitive to atomic oxygen concentration field as an input. Furthermore, as expected, wave patterns projected on simulated satellite images largely depend on the horizontal orientation of the wave propagation. This implies that a tomographic reconstruction is needed when the angle between the wave front and the limb-viewing direction is large. Finally, limitations of the model were discussed.
- PostA 5 MW Wind Turbine Generator System for a DC grid application(2012) Mazaheri, Arash; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIn this work a robust generating system for a 5 MW PMSM wind turbine system with diode rectifier and DC/DC converter connected to DC link has been investigated. The design and efficiency have been studied using MATLAB Simulink and SIMPLORER and the result shows that this system topology has high efficiency. The result found was that the same generator that can provide 5 MW using an IGBT-Converter, can only give 2.5 MW using a diode rectifier and a variable DClink. However, with series and parallel compensations the same generator can provide an output power even more than 5 MW. It was also found that the efficiencies of systems at rated operation with IGBT-converter, diode rectifier with series compensation and shunt compensation are 97.6%, 98.6%, and 98.9%, respectively. Moreover, the systems efficiency at 5% of load are 93.0%, IGBT-converter, 97.3%, series compensation, and 95.3%, shunt compensation. The required reactive power for series compensation and shunt compensation to provide 5 MW output power for the diode rectifier system, at rated operation, are 1.5 MVar and 2.8 MVar, respectively. To conclude, the diode rectifier with series compensation is more efficient for low wind speed (4-11m/s) also it needs less reactive power; however, the shunt compensation scenario has better efficiency at rated speed when the wind speed is higher than 12m/s.
- PostA Bayesian machine learning approach to geostationary infrared precipitation retrievals(2020) Tellwe, Gustav; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Eriksson, Patrick; Pfreundschuh, SimonThis project uses geostationary satellite data to retrieve precipitation rates at surface level. It is achieved through the use of quantile regression neural networks (QRNN) calibrated against rain rates from the Global Precipitation Measurement (GPM) Core Observatory satellite. The area of exploration is located over the Amazon rainforest. The main difficulty of this problem is that geostationary data is not directly related to rain as it only perceives the cloud top temperatures. It does, however, have a high temporal and spatial resolution which makes it interesting for applications in remote areas of the Earth where groundbased radar equipment is unavailable. The result of the project is mainly a comparison between different neural network architectures such as multi-layer perceptron (MLP) and convolutional neural networks (CNN), but there is also a minor comparison to an adapted version of a Hydroestimator (HE) that is currently in use by the National Institute for Space Research (INPE) in Brazil. The best performing configuration, with regards to the loss function, in this study was a CNN. It performed significantly better than the adapted HE for a test conducted over two days in March. An unsuccessful attempt to improve the results using time-series was also conducted. Furthermore, a U-net architecture was also tested on rain rate data that has been resolution-enhanced through interpolation.
- PostA Bayesian machine learning approach to passive microwave precipitation retrievals(2019) Norrestad, Teodor; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and EnvironmentA machine learning-based approach to precipitation retrievals, using Quantile Regression Neural Networks (QRNNs), is developed for data from the Global Precipitation Measurement (GPM) mission. The retrievals are conducted within a Bayesian framework where the networks are trained to predict quantiles of the posterior distribution of rain rates, conditioned on passive microwave observations. In this way, rain rates are retrieved along with the associated retrieval uncertainties. The effects of including additional spatial information as input to the QRNNs are also investigated. Different QRNNs are trained and tested, first globally over oceans and then over the U.S Great Plains. In both cases, the performance of the QRNNs are compared to the Goddard Profiling Algorithm (GPROF), a state-of-the-art passive microwave retrieval algorithm. The primary results are those over oceans, where the QRNNs show great performance on similar levels as GPROF with respect to point estimate metrics such as the mean squared error. Furthermore, the QRNN retrievals are very fast, taking less than a millisecond per footprint on a standard computer. It turns out that extra spatial information improves the QRNNs, especially on making rain-no rain classifications with fractions of true positives and true negatives exceeding 0.67 and 0.96 respectively. Furthermore, the QRNNs manage to produce well calibrated quantiles, resulting in good confidence intervals to account for retrieval uncertainties. Over the Great Plains, the results are promising but are based on much smaller amounts of data and are thus less significant.
- PostA Carbon Footprint Assessment on Construction and Maintenance Operations for the Port of Gothenburg - With emphasis on emission reduction actions(2014) Sarbring, Anna; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentPorts are an industry that emits high levels of CO2 missions. The purpose of this thesis is to minimise CO2-eq emissions from the Port of Gothenburg. Four main objectives are used to achieve this purpose. The first is mapping ports, with respect to CO2-eq emission related activities and reduction targets. Four ports are selected in this report, located in Antwerp, Gothenburg, Los Angeles and Valencia to determine different emission reduction actions. Such actions are a combination of technical development, using same equipment but more efficiently or by change of behaviour. Since no ports have estimated CO2-eq emissions from construction and maintenance operations before, this report serves as a foundation or inspiration for further development of CO2-eq calculations. Emissions from construction and maintenance operations are defined as indirect emissions for Gothenburg Port Authority. The second objective is to collect data for the mass of materials and volume of fuels used in construction and maintenance operations for the Port of Gothenburg. Data from year 2013 is used for the collection of used materials and energy related products. The study includes the 22 most extensive projects out of 160 construction and maintenance related projects. The third objective is to calculate and asses CO2-eq emissions from construction and maintenance operations for the port of Gothenburg. The chosen method for calculating emissions is a carbon footprint assessment and includes a CO2-eq inventory on construction and maintenance operations at the Port of Gothenburg. The carbon footprint assessment uses emission factors in all calculations. The material and energy related products that contribute the most to CO2-eq emissions are fossil fuels and concrete. The total CO2-eq emissions for the 22 projects are approximately 1340 tonnes and in mass approximately 1060 tonnes (excluding fuels). This leads to an increase of 1 % of the current carbon footprint for Gothenburg Port Authority. If using an uncertainty factor with 25 % and including all 160 projects, CO2-eq emissions during 2013 are estimated to be up to 5600 tonnes, which is an increase with 3 %. The conclusions from the mapping and carbon footprint serve as a foundation for the development of guidelines, which operates as emission reduction potential areas. This is the last objective, including suggestions for guidelines on how to reduce CO2-eq emissions in port operations.
- PostA case study of landfill gas potential at Kikås landfill - Assessment of environmental impacts and alternatives for mitigation(2014) Larsson, Jonas; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis thesis evaluates three different theoretical models to estimate landfill gas potential. Specifically, a case study to assess the gas potential at Kikås landfill and alternative mitigation measures has been conducted. Recent years, the waste sector has been increasingly acknowledged as a major contributor to emissions of greenhouse gases. A large part of these emissions are emissions of landfill gas (LFG). LFG consists of approximately 50 % carbon dioxide and 50 % methane. Methane is a strong greenhouse gas, which makes mitigation measures viable. On the behalf of the municipality of Mölndal, a case study was conducted with the aim of evaluating gas potential, environmental impact and options for mitigation if needed. A major threshold for conducting estimations of LFG potential is the major uncertainties related to both model parameters and site specific waste data. These uncertainties were to some extent evaluated by using three different models for estimation of LFG potential: the U.S EPA’s waste model LandGEM, IPCC’s waste model and the Dutch Afvalzorg’s model. The case study indicated a likely remaining gas potential of 2 100 – 3 250 ton methane for year 2015–2035,which is significant with respect to global warming. Nonetheless, uncertainties in estimated gas emissions are large. Therefore an investigation of actual gas flows by conducting test pumping is recommended.
- PostA Commercial Model for Eco-efficient Production of Biogas from Sewage Sludge in China - Upgrading biogas to vehicle-used bio-methane(2012) Zhao, Lei; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and Environment
- PostA Comparison of a 5 kW Full-Bridge Converter Using IGBT’s and SiC BJT’s(2008) Bergman, Niclas; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentIn this master thesis work, a 600/28V full-bridge DC/DC converter has been designed and investigated regarding its efficiency. As switching elements a SiC BJT and a conventional IGBT has been used. In addition, the Ebers-Moll parameters have been identified for a conventional BJT and the SiC BJT. Comparisons of the converter with the SiC BJT setup and the conventional IGBT setup have been made by simulations in MATLAB/Simulink. It was found that estimating the losses of the SiC BJT was not possible. Calculations of losses in the transformer and filter inductor of the DC/DC converter have also been made.
- PostA Complex Systems Approach to Human Cultural Evolution(2013) Allen, James; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis thesis will use two abstract computational models to investigate a number of outstanding questions related to human cultural evolution. Using simulations explanations for a number of phenomena within the archaeological record will be put forward. These will include the discontinuous cultural evolution patterns, the broadening of human diet and the extinction of the Neanderthals. The central theme throughout these findings is that it is the delity of transfer, and by extension the increase in complexity of early hominid culture, that constrains the subsistence strategies used within the Palaeolithic era, whilst the form of the resources dictates the form that these strategies will take. Key to these dynamics is the territorial competition between groups, with a more diverse strategy leading to more efficient groups that can encroach on the less efficient, reducing the carrying capacity and causing the population to move below the minimum group size allowed, thereby becoming extinct.
- PostA conceptual model for energy, trade and economy(2013) Nilsson, Olof; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis thesis focuses on introducing and incorporating an explicit model for energy trade into a conceptual model for economy and energy. The inclusion of an energy market into the model where countries can buy and/or sell energy to a market price is something that was not done in the model that was used as a starting point for this study. In general, energy systems models use less explicit mechanisms to determine trade, like e.g. shadow prices from optimisation. This kind of trading model is successfully developed and introduced into a more complex, dynamic model for economy and energy. The trading mechanism is analysed extensively in itself before introducing it into the more complex model. This to ensure that it exhibits the behaviours that one would expect to observe on a market. The effects of introducing energy trade into such a more complex, dynamic model for economy and energy is then explored and it is shown that when at least one country is sitting on large enough fossil fuel assets, the possibility of energy trade will inhibit the development of renewable energy for all countries. Moreover, the possibilities of avoiding definite time effects in model simulation by modifying the utility function that is subject to optimisation is studied. It is shown that it is possible to find a utility function that in many aspects avoid the definite time effects.
- PostA coupled immunological and epidemiological model for exploration of immunization strategies(2021) Rylander, Kevin; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Andersson, Claes; Andersson, Claes
- PostA feasibility study for electrofuel implementation with waste-to-energy plant(2015) Rungruengsaowapak, Chantat; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentElectrofuel or Power-to-Gas is paid by great attentions nowadays since it could mean to reduce the fossil fuel dependency by renewably production of combustible gas. Main application of gas could be to supply a clean fuel for vehicles which means if the technology is feasible, share of greener energy in transportation sector’s energy mix would be greatly increased. Despite having many studies focused to implement the technology with biogas facilities, very few concentrate on feasibility to apply the same technique with conventional combustion process like waste-to-energy process. Hence in this study, the electrofuel technology of Sabatier reaction, which uses renewable electricity, water and carbon dioxide to produce methane, is examined by integrating with a case study waste-to-energy plant. The study mainly considers the economic feasibility of the combined process of Sabatier and carbon capturing process while perspectives on technical term are also discussed in parallel. Capacity of the process is varied with extreme waste-to-energy plant’s electricity and emission outputs to define the gas production potentials. Profitability of different process sizes is determined as well as sensitivity analysis on key economic parameters such as synthetic natural gas (SNG) price, electricity price or change in investment cost. The work also takes into the account some change due to season that has significant effects to both rate of energy production and relevant profitability. The results show that the integration is feasible especially when the SNG price is high which is likely in the near future. When the process size increases, the change in investment cost plays less important role in total process cost. It can also be observed that such change in production capacity, break-even points of SNG price decreases while reverse trends can be gained in case of electricity price. Besides variation on key economic parameter, another critical factor is electrolyzer efficiency which operating cost can be significantly lower when more efficient electrolyzer is used.
- PostA Framework for Sustainable Renovation in the Inventory Phase - A case study in Gamlestaden, Gothenburg(2016) Böber, Elisabeth; Cardoso Martins, Maria Julia; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis thesis was written in Challenge Lab, a hub for integrative and transformative thinking at Chalmers University of Technology, where students are in the centre of academia, private, and public sector, acting as change agents to tackle sustainability development challenges. Through analysing the present situation of Gothenburg regarding urban development, major challenges were identified. Through the Backcasting method, the research problem has been analysed from different perspectives and with different disciplinary impact. One major deficit is the renovation of old building stock within the city of Gothenburg, especially multi-dwellings. There have been many attempts in research to achieve a sustainable renovation concept. Yet, industry and property owners focus mainly on energy efficiency, meaning the environmental-economic perspective rather than the social or well-being dimensions. In order to achieve a sustainable renovation, the different sustainability dimension need to be balanced and enhanced by an architectural and cultural-historical aspects. A case study of a renovation in a multi-dwelling in Gamlestaden, Gothenburg, was conducted. Interviews were held with the tenants, the property owner, an independent renovation consultancy company, and several experts, in order to understand the complexity of a renovation. It provided important insights into the practice of industry, and it was found out that the renovation framework provided by Boverket is rather insufficient and vague on how to proceed in the inventory phase of a renovation process. Therefore, the major outcome is a revised framework for the inventory phase of a renovation process, as it was found out this is a crucial phase to achieve a sustainable renovation
- PostA life cycle assessment of different fuel alternatives for Gothenburgs public transportation system(2015) Ghiassi Tari, Parisa; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentOne of the solutions for implementing a sustainable transport system, is to increase the use of public transportation and replacing fossil fuels with biofuels. In Gothenburg’s public transport system, there are no fuel alternatives that dominate the market yet. Currently, Volvo have stopped manufacturing biogas buses and instead changed focus towards electrified hybrid buses. The decision has concerned the biogas industry that expects a future competition between renewable fuels in Gothenburg. The purpose of this thesis is to assess and investigate the competitiveness of biodiesel (RME), biogas (from sewage sludge) and biodiesel plug-in hybrids for public buses in Gothenburg. Objectives include, a well-to-wheel life cycle assessment (LCA) for the different fuel alternatives that will indicate their environmental performance, and a survey that aims to indicate possible market potentials and barriers. The following environmental impact categories were included in the LCA: Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP), Photochemical ozone creation potential (POCP), and Particles (PM). The results indicate that the environmental impacts per MJ fuel of biodiesel plug-in hybrids in the categories GWP, AP, POCP and particles are small compared to petrodiesel. Biodiesel performs well in comparison to petrodiesel in GWP and POCP. Biogas has the best environmental performance in the impact categories EP and PM while plug-in hybrids have the best environmental performance in GWP and POCP. However, if the batteries are included in the LCA plug-in hybrids, they have the highest environmental impacts among the three renewable fuel alternatives. Petrodiesel has the best environmental performance in AP. The survey indicates that cost and policy targets are the driving market barriers, but also that market potentials can be strengthened through introduction of emerging fuel technologies and better cooperation between stakeholders. Based on the Euro IV emission standard, all analyzed fuels have in general lower environmental impacts per MJ fuel compared to petrodiesel. Therefore, the competiveness of renewable fuel alternatives in Gothenburg, isn’t primarily based on their relative environmental performance. Cost and social aspects are potentially important aspects that should be further investigated. It is also recommended to perform more LCA studies, with different scope, functional unit, allocation methods etc., to better understand the environmental performance of different fuel alternatives.