Energía y Ambiente (ITBA-KIT)

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  • Tesis de maestría
    Investigation of a novel compression concept for fuel cell stacks
    (2023-07-17) Weis, Daniel; Haußmann, Jan; Kharrat, Jamil; Müller-Welt, Philip
    The usage of hydrogen in fuel cells gains more and more importance due to the need for emission-low alternatives in various technical areas. The focus of this work lies on the polymer electrolyte membrane fuel cell. One parameter to reduce performance losses is the contact pressure between the bipolar plate and the gas diffusion layer. It is influenced by first the assembly force and second the swelling of the membrane during operation which is caused by changes in temperature and humidity. To improve the stress distribution and to keep the stress increase during operation low, a novel compression concept is proposed and investigated in an FEM analysis. Different variants of springs are compared to each other and to the reference, a disc spring stack on tie rods. The results show that an even stress distribution is achievable through a concept with 15 small springs where the force flow enters the end plate at various points over the stack. High contact pressure at the edges of the active area can be reduced by reducing the end plate bending. This is achieved by moving the springs closer together so that the inner springs touch each other. A difference between minimum and maximum stress along one path in the cross-section of 0.2-0.4 MPa is achievable and of 0.9-1.3 MPa along the longitudinal section. It is found that the stress increase from assembly to operation depends on the spring characteristic. The maximum increase at the edge of the active area can be reduced to 1.7 MPa, and the smallest stress increase in the centre of the active area is around 0.5 MPa. The proposed concepts show better results than the disc spring reference with a good stress distribution. Although the stress increase in the proposed concepts is also better than in the disc spring stack the value is not yet satisfactory because it strongly influences the porosity of the GDL during operation. The most promising spring concept is tested experimentally. The experimental results show a qualitative accordance with the simulation.
  • Tesis de maestría
    Feasibility study of shallow geothermal heat pumps to meet the thermal demand of a typical household in Córdoba, Argentina
    (2023-09-22) Iriart, Mariné; Smoglie, Cecilia
    Esta tesis de maestría es un estudio de factibilidad del uso de energía geotérmica, en viviendas tipo de un desarrollo urbano de la ciudad de Córdoba, Argentina. El calor geotérmico a temperatura constante disponible a poca profundidad, se propone como fuente de una bomba de calor acoplada a un piso radiante para aire acondicionado y a un termotanque para suministro de agua caliente sanitaria. El estudio se realizó considerando las características del clima local, la demanda de energía de una casa residencial típica y las factibilidades técnicas y económicas de la región. Primero se describen la matriz energética argentina, la demanda de energía residencial, las tecnologías renovables aplicadas para abastecer esa demanda y el actual uso de la energía geotérmica. Luego se dimensionan bombas de calor geotérmicas para usos residenciales, se comparan los resultados de ahorro energético y de reducción de gases de efecto invernadero con las tecnologías convencionales y se realiza una evaluación económica. Se concluye que bombas de calor operando entre reservorios geotérmicos a baja profundidad y sistemas de suelo radiante y/o termotanques, surgen como una tecnología eficiente para cubrir necesidades de climatización y calentamiento de agua, mediante uso de energía renovable y limpia.
  • Tesis de maestría
    Energy-efficient operation of an industrail evaporative cooling
    (2023-05-15) Ferraris Montenegro, Nahuel; Markus, Nickolay
    This thesis aims to develop a model for an industrial evaporative cooling system having a chiller and a production heat source using two cooling towers to evaluate the energy consumption of the system and find an optimal approach to minimize energy consumption without incurring investment costs. To achieve this objective, the thesis will perform a comprehensive analysis of the optimal cooling system configuration, considering various factors such as the ambient wet bulb temperature, the chiller cooling requirements and the maximum water temperature required by the production heat source. The proposed methodology consists of developing a function for the cooling tower outlet water temperature and chiller power consumption, implemented in a Dymola numerical model. The study will investigate different control strategies and scenarios to determine the optimal approach for minimizing energy consumption. It is essential to note that while this research focuses solely on the development and testing of the model using simulation data, real plant data validation is not included in the scope of this study. Rather, the emphasis is on demonstrating the feasibility and accuracy of the model through rigorous testing and analysis. The expected results include the development of an efficient model and suggestions with the intention of reducing energy consumption and improving overall efficiency. The findings of this study will provide valuable insights into optimizing industrial cooling systems and may serve as a basis for future research that includes real plant data validation and practical implementation.
  • Tesis de maestría
    Concept and design of a high power dense propulsion system for electric aircraft
    (2023-10-02) Beneke, Lennart; Reuter, Steffen; Berg, Lars-Fredrik
    The present thesis proposes a conceptual design of a tiltable propulsion system for the ALBACOPTER® 1.0, an eVTOL aircraft with a take-off mass of800 kg. Usually, the propulsion systems of eVTOLs are direct drives due to their simple design. However, since the propeller thrust in relation to the take-off mass is the most important criterion for vertical take-off aircraft, power-dense drives are of maximum importance. Therefore, a propeller drive concept combining a high-performance synchronous machine with a gearbox is developed and investigated with regard to its performance. For this purpose, all boundary conditions are determined. First, the propeller is simulated in order to define its relevant speeds and gear’s reduction ratio. Then the aerodynamic loads are estimated using data from wind tunnel tests and CFD simulations and qualitatively compared with own wind tunnel tests. It is shown that the moments induced by oblique propeller inflow play a significant role compared to the lateral forces. By calculating and classifying these and other potential loads, concepts for the drive train and the tilt actuator are developed and evaluated.
  • Tesis de maestría
    Machine learning for spatial disaggregation of regional transport data in the EU
    (2023-06-23) Fernandez, Juan R.; Ates, Cihan; Patil, Shruthi
    The European Union (EU) is actively working to combat climate change and promote sustainable development by reducing greenhouse gas (GHG) emissions. The transport sector, a major contributor of GHG emissions, was at the forefront of these initiatives. After experiencing steady growth from 2013 until 2019, there was an abrupt decrease in 2020 due to the COVID-19 pandemic. However, preliminary estimates indicated a rebound of 7.7% for transport emissions in 2021, according to the [Agency (2021)]. Nonetheless, further research is necessary in order to devise effective strategies for regional decarbonization within this challenging sector. An analysis of the transport sector in Europe reveals significant disparities in emission trends across different regions. According to [Eurostat (2021)], Western European countries have generally experienced greater decreases in transport emissions compared to Central and Eastern European nations, which have made slower progress. Furthermore, the European Environment Agency [Agency (2021)] points out that urban areas tend to have higher emissions due to higher population densities and greater demand for transportation. These discrepancies underscore the necessity for spatial disaggregation when developing tailored decarbonization strategies for different regions. To address the intricacies of regional decarbonization potentials, this research aims to apply machine learning techniques to enhance the accuracy of estimating transport-related metrics at a regional level. This, in turn, will facilitate the identification of decarbonization opportunities within the transport sector. More precisely, the study seeks to establish a framework that utilizes machine learning methodologies for spatial disaggregation, a critical process for understanding the factors that influence emissions on a regional scale and devising efficient mitigation strategies.
  • Tesis de maestría
    An economic evaluation on hydrogen production technologies and hydrogen applications
    (2023-04-02) Allende, Javier F.; Badea, A. F.
    The main objective of the study is to present a comprehensive and, above all, updated overview of the hydrogen demand and supply situation. The physical and chemical properties of hydrogen are presented, together with an explanation of its major advantages and disadvantages as an energy carrier compared to other fuels currently in use. It also explains the importance of hydrogen on the world stage, as one of the main vectors for sustainable economic development worldwide. There are numerous uses for hydrogen nowadays. It can be used, for example, as a feedstock in several industrial processes, as an energy carrier or reserve, and as one of the main fuels to decarbonise transport. This work explains the current situation of hydrogen demand, showing the most relevant applications at present and those that are emerging as highly probable alternatives in the short term. Furthermore, estimates of future hydrogen demand are also presented. Regarding hydrogen production methods, firstly, a technical analysis is presented, explaining the characteristics of the different production methods available at present. Subsequently, an analysis of production costs is carried out, taking into account the main alternatives. A sensitivity analysis is also carried out on these alternatives to appreciate with clarity which are the factors that have the greatest impact on the final cost of hydrogen production for each method. One of the most notable conclusions of the report is the fact that, at current fossil fuel prices and associated emissions costs, zero- or low-emission hydrogen production methods are cost- competitive against hydrogen produced from natural gas (the most widely used technology today). It is also highlighted how the global context of recent years has led to an accelerated development of hydrogen technologies and their deployment.
  • Tesis de maestría
    Design study of the MoNiKa-ORC-turbine and comparison with experimental results
    (2023-03-31) Niño Avella, Cristian Leonardo; Wiemer, Hans-Joachim
    The main objective of the project is to develop, verify, and validate a MATLAB code which implements a mean-line analysis for the ORC-Turbine located in the MONIKA facility. The mean-line analysis method is a useful tool to design turbomachines. In this study it was used to simulate and analyze the performance and properties into the turbine, under different operating conditions by analyzing its properties in a mean radius for each one of the inside inlet and outlet cross sections of the stages. It was taken into consideration different loss correlations in order to achieve a better result. For the implementation of the mean-line analysis, the geometry and design properties for the ORC-Turbine were used, along with the experimental data obtained from the MONIKA facility in previous works. These data were used for the verification and validation process, ensuring that it accurately represents the behavior of the turbine under different scenarios. The MATLAB code was designed to implement the mean-line analysis method, which can simulate the performance of the ORC-Turbine under various operating conditions, such as different mass flow rates, inlet and outlet temperatures, and pressures. The results of the mean-line analysis showed that the developed code can accurately predict the performance and the properties of the ORC-Turbine, within a reasonable level of accuracy. The code can also be used to evaluate the impact of different design modifications, such as changes in the inlet and outlet thermodynamic properties of the fluid, on the turbine's performance.
  • Tesis de maestría
    A layout of the tritium plant subsystems for the european demonstration fusion power plant
    (2023-03-28) Constantin, Federico Miguel; Schwenzer, Jonas
    The European demonstration fusion power plant (EU-DEMO) project intends to prove the commercial viability of nuclear fusion as a source of safe and clean energy. This fusion power plant will be fueled by a 1:1 deuterium-tritium (hydrogen isotopes) mixture that will need to be recycled for environmental and economic reasons due to the low burn-up fraction. Tritium is a radioactive isotope that requires a special design of any handling facilities to be “tritium compatible” and a series of layers of protection to prevent any release of tritium to the environment above the permitted values. Moreover, tritium is scarcely available which makes it again crucial to design the tritium systems, the so called fuel cycle, such that the inventory is minimized. The EU-DEMO fuel cycle will be housed inside two buildings, the tokamak building and the tritium plant building. The first one will contain the reactor, its fueling systems and the direct internal recycling loop. The tritium plant building, which is the subject of this work, will accommodate an inner tritium plant loop and an outer tritium plant loop. In this thesis, a methodology for estimating the required footprint of the tritium plant and optimizing its layout is proposed. This is accomplished by identifying all the necessary equipment of the plant, estimating their physical dimensions, and allocating them into primary and secondary confinements (e.g. gloveboxes and rooms), for which their footprint and volume is obtained. By arranging these rooms inside a multistory building, the final layout is achieved. This methodology takes into consideration the fuel cycle processes and at the same time defines personnel and process safety, construction, operation and maintenance criteria to obtain an optimized layout suitable for the entire life cycle of the facility, while keeping in mind the need for minimizing the tritium inventory. Afterwards, this work puts forward a piping dimensioning strategy, defining design basis and calculation sequences supported on European Norms as well as optimization criteria to achieve a reasonably low tritium inventory in piping required to connect confinements and rooms. The presented tritium inventory determination focuses on the piping under normal operation of the plant, while the inventory inside the units is out of the scope of this work, even though it is taken into account for the development of the layout. The application of the developed methodologies resulted in the identification of 627 process equipment which have been grouped into 29 gloveboxes, 2 coldboxes and 19 metalboxes. These confinement structures can be housed inside a compact seven-story-building design, with a projected footprint of 2200 m2, a cumulative footprint of 11240 m2, an external volume of 57030 m3 and external dimensions of 35.8 m of height, 74.0 m of length and 30.9 m of width. Lastly, the resulting tritium inventory inside interconnecting pipes under normal operation is found to be in the order of 0.2 g with only 10 pipe types (outer diameter and thickness combinations).
  • Tesis de maestría
    Design of a MoNiKa-turbine and condenser model in Modelica/Dymola and comparison with previous Simulink models and experimental results
    (2023-03-06) Maier, Mirco; Wiemer, Hans-Joachim
    To research optimization possibilities in supercritical ORC processes for geothermal power production the Modular low-Temperature Circuit Karlsruhe (MoNiKa) was built at Campus North of the Karlsruhe Institute of Technology. Several research tasks have been conducted over this installation focusing on individual components. The present master thesis describes the development of a coupled MoNiKa turbine-condenser model using the Modelica modeling language with the Dymola development environment. For thermodynamic components the commercial library TIL was used. To calculate the properties of the working fluid a Dymola-REFPROP interface was utilized. For the turbine model an empirical efficiency correlation of the MoNiKa turbine was developed from experimental data and implemented. The determination of the turbine inlet pressure is based on Stodola’s cone law which has been adjusted to the MoNiKa turbine in previous studies. To reduce computational time the input data has been pre-processed by applying filters. For the condenser model grid convergence studies were carried out to ensure precision and convergence. The simulation results of the developed models were compared to the results of previous Simulink models for turbine and condenser. The model was then validated using experimental data from several MoNiKa test runs from 08-10 November 2021 representing a range of different operating conditions. The quantitative and qualitative agreement of the simulated turbine shaft power with the experimental data could be improved compared to the previous models. The developed coupled turbine-condenser model is capable of providing close approximations of turbine shaft power and condenser outlet variables over a wide operating range of the MoNiKa plant. In addition, the computation time could be kept within reasonable limits to enable further extensions of the model to complete the MoNiKa cycle. The influence of individual input parameters on the output variables could be determined by means of a sensitivity study to guide further improvements in the measuring equipment.
  • Tesis de maestría
    Development of an end-effector for an industrial robot for the automates integration of threaded inserts into a hybrid additive manufactoring process
    (0022-01-28) von Deyn, Lennart
    In this thesis, a novel approach to automatically install threaded inserts into additive manufactured parts is developed and validated. Such an approach is highly relevant in the context of process automation and production of function-integrated parts. Automated production in combination with additive manufacturing has the potential for resource and energy-efficient production. This is becoming an increasingly important factor during decision making, due to climate change. Furthermore, additive manufacturing can support the development of climate-friendly solutions across all fields of application, as it enables quickly adaptable designs and flexible production methods. In addition, new design approaches to produce function-integrated components are becoming available. Integrating mechanical and electrical functional components during manufacturing makes it possible to realise an efficient and cost-effective integration procedure. The Fused Filament Fabrication (FFF) process can be used for this purpose, as it allows easy automation and expandability compared to other additive processes, plus a wide variety of materials can be processed. Initial literature research on the state of the art shows, that currently no process has been described, that combines the FFF process with a subtractive process and conductive filament. The 4K-FFF unit, the subject of this thesis, offers a unique approach to the automated production of function-integrated components. The system consists of a multi-material FFF printer with a milling and handling module. Manufacturing inaccuracies resulting from the FFF process can be compensated by the milling module. An industrial robot on the handling module is used to add functional components to the process. This setup enables the fully automated production of function-integrated components. For fastening and contacting the function-integrated components, threaded inserts are used, which have to be installed manually due to a lack of a suitable alternative. Literature research shows that there are no methods for the automated installation of threaded inserts into individual components, which are common in FFF. This shortcoming is addressed in this thesis. A new end-effector for the industrial robot is developed, which can grip, heat and install threaded inserts into a component. In addition, a quick-change system is established. Both expansions further increase the degree of automation of the 4K-FFF unit. A parameter optimisation procedure is carried out to determine the ideal operating parameters for the new end-effector. The functionality of the development and the quick-change system is validated by the production of demonstrator components.
  • Tesis de maestría
    Experimental examination of the MoNiKa-ORC-Turbine and comparison of the results with thermodynamical calculation
    (2022-04-11) Mardon Pérez, Joaquín; Schulenberg, Thomas; Hans-Achim, Wiemer
    The aim of this work is to understand the propane turbine behaviour located at MoNiKa facility in Campus North (KIT). Starting with the thermodynamic simulations, continuing with the selection of different load points to evaluate them experimentally on site and ending with the data analysis to finally reach the correction of the Stodola’s law equation and the turbine efficiency correction. The simulations were performed using GESI software developed in MATLAB® by ITES, and in addition, to perform these simulations, all the calculations of the thermodynamic properties were performed with the REFPROP software, NIST fluid properties database. The working medium of this work is either propane or a mixture between propane and nitrogen. The runs were carried out at the beginning of November 2021, where different types of assays were performed, previously analysed in GESI. First a test of different turbine load points was performed, the following day the response of the turbine was evaluated by progressively opening the turbine control valve and, the last day, another sensitivity test was performed, but this time the turbine was evaluated with the response of a progressive increase of the mass flow rate through the turbine. Stodola's equation provides a calculation method for the highly nonlinear dependence of the turbine inlet pressure with a flow for a multistage turbine with high backpressure. From its correction we find its behavior for this turbine. In turn, we sought to understand the dependence of the turbine efficiency, and an equation that solves it within certain boundary conditions. The current experiment performed during winter semester 2021/2022 and is the continuous work of previous thesis and experiments at the facility. Each test performed in MoNiKa brings the possibility to increase the know-how of the facility and optimize the performance of a Binary ORCs (supercritical organic Rankine cycle) power plant with a low temperature geothermal heat source.
  • Tesis de maestría
    Experimental investigation of the combustion properties of CO2 diluted CO-O2 mixtures with variation of initial temperature and pressure
    (2022-03-15) Torres de Ritter, Eugenio Luis; Veser, Anke; Kuznetsov, Mikhail
    With the increasing relevance of energy transition, synthetic fuels have arisen as an alternative to storage green energy. In the processing of this fuels, carbon monoxide is widely used. Understanding the behaviour of the combustion of this gas is of high importance. To date, very limited knowledge is available on how combustion of carbon monoxide behaves alone or diluted with carbon dioxide as much focus were given towards mixtures that included hydrogen and water. The focus of this work is to investigate the combustion of carbon monoxide in dry ambient and characterize the flame speed of the combustion through two different methods, the Shadowgraph Method and the Constant Volume Bomb Method. For this purpose, combustion experiments in an explosion bomb were conducted. An experimental matrix of nine different initial pressures-temperature combinations and five different mixtures of CO-O2-CO2 were tested.
  • Tesis de maestría
    Methodology for energetic and economic evaluation for the geothermal heat exploitation in an industrial facility
    (2022-02-21) Wagner, Federico José; Kuhn, Dietmar; Fraguío, Martín
    This work aims to analyse the use of low enthalpy geothermal heat in Bahía Blanca by evaluating different alternatives when using it in a specific project. In Bahía Blanca, Argentina, several boreholes with geothermal water have been used for many years. Although there are ageing wells in this area, many of which are proof of the existing considerable geothermal potential, only a few are deemed heat sources. The first section introduces general concepts for the contextualisation of the document. Then, the second section details all the performed methodology and an explanation about the selection of the industrial case is given. Then, the industrial system and pipelines are presented, followed by a description of the mass and energy balances. Later, the heat pump calculous, economic evaluation and CO2 footprint analysis procedures are presented. Finally, the fourth section presents all the obtained results in graphics and tables, and at the end, the conclusions are assessed.
  • Tesis de maestría
    Sensitivity study and improvement of a film cooling configuration of a high-pressure turbine blade
    (2022) Giménez, Juan Ignacio
    Much effort has been expended in the aerospace industry in order to achieve the highest quality standards required for nowadays technical and environmental necessities. This involves the increase of specific power and overall engine performance, together with the reduction of noise, specific fuel and heat to fuel consumption. Fundamentally, thermal efficiency and power output increase while increasing turbine rotor inlet temperatures. For this purpose, it is necessary to optimize engines with regard to the overall thermodynamic process. Advanced gas turbine engines operate at high temperatures to improve thermal efficiency and power output. As the turbine inlet temperature increases, the heat transferred to the turbine blades also increases. The level and variation in the temperature within the blade material, which causes thermal stresses, must be restricted to achieve reasonable durability goals. The operating temperatures for aircraft engines are far above the permissible metal temperatures, therefore it is necessary to cool the blades internally and externally. The blades are cooled by extracted air from the compressor of the engine and, since this extraction incurs in a reduction of thermal efficiency, it is necessary to understand and optimize the cooling techniques, operating conditions, and turbine blade geometry. Increasing demands confront the cooling systems of turbine blades. High temperature material development, such as thermal barrier coating (TBC) or highly sophisticated cooling schemes, are a necessary challenge to overcome, in order to ensure high-performance gas turbines for the upcoming years. The suggested designs hereby are to achieve an optimum cooling by a minimum use of cooling air and minimum aerodynamic losses which are an unwanted consequence of film cooling injection. Cooling techniques in advanced gas turbine engines can be distinguished between internal and external cooling. In convection cooling or internal cooling, the secondary flow extracts the heat flux through the blade walls and transports it away via channels inside the turbine blade. A vast amount of studies for different types of geometry arrangements have been carried out and applied, in order to increase heat flux transfer. These geometries include rib turbulators, pin fins, dimpled surfaces, surfaces with arrays of protrusions, swirl chambers, and rough surfaces. For external cooling, film cooling technology made possible the nowadays achievements in high efficiency gas turbine engines. The art and science of film cooling concerns the bleeding of internal cooling air through the external walls to form a protective layer between the hot gases and the component external surfaces. The application of effective film-cooling techniques provides a reliable defense for hot gas path surfaces against the high heat fluxes, serving to directly reduce the incident convective heat flux on the surface. Several investigations have been made regarding the major effects of cooling holes arrangements, turbulence, interaction between flows and vorticity production in order to improve film cooling technology. To address the main challenges of designing an optimal film cooling configuration, it is necessary to understand the behaviour of the main gas flow and the coolant flow. For this purpose, CFD calculations are carried out to visualise and understand the complex physical phenomena under study. However, numerical models should be validated with experimental data as this path leads not only to the understanding of the physical phenomena involved in the experiment, but also provides correct guidance on how the different variables under study can lead to engineering improvement. A test rig at the Institute for Thermal Turbomachinery (ITS) at the Karlsruhe Institute of Technology (KIT) is used to validate the related CFD set-up. In this work, a sensitivity study of different conventional film cooling configurations is introduced. This involves the study and modification of different geometrical variables in specific regions of the blade. Also, the complex vortex structures generated due to the interaction of the main hot gas with the coolant, that enhances heat flux transfer through the blade, is analysed. The most promising configurations in terms of blade temperature reduction, will be considered as possible candidates for blade manufacturing
  • Tesis de maestría
    Design of a MoNiKa-ORC-turbine model in Simulink and comparison with experimental results
    (2022) Filipe, Julia; Schulenberg, Thomas; Wiemer, Hans-Joachim
    This work consists in the development of a computational model for the steam turbine currently operational in MoNiKa test facility plant, located in KIT-Campus Nord, Germany. Given that this corresponds to the first attempt to model the mentioned turbine, the selected approach was to elaborate a highly simplified model that considers the system as a whole, unique element, and therefore calculates in terms of the turbine’s inlet and outlet parameters. The development was made in Simulink, using a basic configuration of blocks and features, and also some specific parts were coded in MATLAB. The building process resulted firstly in a simplified version of the model that supports constant inputs and outputs and consequently is independent of time; and a final version that supports time-dependent inputs and outputs, and can be employed to simulate transient operation conditions. The validation was made using real data provided by the plant, with a selection of several cases that reflected different operation conditions. Final results showed that the model is successful in predicting stationary operation cases, and also achieved good results with some transient operation conditions that presented progressive variations. However, the model is not suitable for simulation of fast-varying conditions.
  • Tesis de maestría
    Development of the processing step from MOF to supported catalyst by electrospinning
    (2022) Alvarez, Macarena; Maletzko, Annabelle
    In order to increase the flexibility of renewable energies and improve their integration into existing energy grids, efficient intermediate storage is necessary. High-purity hydrogen produced in a water electrolysis cell is a suitable energy carrier. However, the use of some electrolyzers is associated with high costs due to the required use of precious metals as catalysts, while others have disadvantages in terms of load modulation. In this sense anion exchange membrane water electrolysis (AEMWE) arises as an attractive alternative technology that combines convenient features of other type of electrolyzers. Nevertheless, there is a necessity in improvement regarding the performance of AEMWE. The oxygen evolution reaction (OER) in the anode, is the major source of energy loss and therefore, there is potential to optimize OER catalysts. In this work, supported catalysts for the OER were developed using Metal-Organic Frameworks (MOF74) dopped with Ni and/or Co and fibers obtained from an electrospinning process, as supporting material. The MOFs were pyrolyzed to obtain a carbon scaffold with finely dispersed transition metals, as well as the polymer fibers, which structure the catalyst, allowing to tune conductivity and mass transport. Two different routes for combining the MOFs with the fibers were studied. In order to investigate the electrospinning process, polymer concentration, solvent, applied voltage and polymer were varied. The improved parameters were selected and Polyacrylonitrile (PAN) fibers were successfully electrospun and pyrolyzed. The MOFs were characterized physically, chemically and electrochemically. Pure Ni-MOF74 showed increasing current along the Cyclic Voltammetry cycles, reaching a mass-specific current of 732 mA mg -1 after 50 cycles. A supported catalyst was obtained after impregnation of the Ni-MOF74 over the pyrolyzed fibers and characterized. The combined catalyst showed a similar behavior compared with the pure Ni-MOF74.
  • Tesis de maestría
    Machine learning-based analysis of residential electricity consumption behavior for consumers and prosumers
    (2021) Werner, Tamo; Jiao, Jiao
    With the shift towards a more sustainable energy system, the need for a better understanding of the behavior development over time of consumers and prosumers arises. Despite the growing penetration of smart meter infrastructure, the availability of energy usage behavior data is still limited, due to privacy and security concerns. Thus, connecting and comparing existing datasets is the key to observe the user behavior shifts as well as enhancing the utility of the available data. In the present work, a novel work!ow for combined analysis on multiple smart meter datasets is proposed, which links datasets with diferent scopes, temporal origins and speci#cations. In general, there are 4 steps: data preprocessing, clustering, location dependency check and dataset linking. First, the meteorological seasons combined with weekdays and weekends are picked for data segmentation in the data preprocessing, followed by missing value validation and normalization based on the maximum and minimum consumption value of each household. Thereafter, K-means clustering algorithm is applied to group the user behaviors, which stands out by 0.8186 Silhouette coe$cient (SIL) and 0.2884 Davies-Bouldin Index (DBI) among Fuzzy C-Means and hierarchical clustering approach. Subsequently, two validation approaches on the location dependency, cluster center correlation (0.8048) and location share among clusters (4.99 % variability), prove the minor impact of the household location on the electricity consumption behavior within Germany. Based on the location dependency check, ultimately, the combined analysis of the two datasets reveals the temporal development of the residential consumption behaviors. It shows that new technologies, especially Photovoltaics (PV), Electric Vehicles (EV) and heat pumps, have in!uence on the user behavior shift and the energy consumption level.
  • Tesis de maestría
    Investigations on energy optimal solutions to control a forestry crane
    (2021) Schulz, Tim; Geimer, Marcus; Geiger, Chris
    Due to the progressing climate change, climate-neutral resources are becoming increasingly important. The forest industry is aware of this problem and hence, is looking for new technologies to make the production of its natural resource more ecient. Therefore, this thesis presents an energetic optimization of a forestry crane. For this purpose, a pseudoinverse solution of the crane kinematics is optimized by the gradient projection method according to minimum hydraulic pressure and ow rate. The hydraulic pressure reveals to be the relevant optimization parameter. By increasing the feedback pressure, its inuence on high-pressure peaks is increased in order to successfully reduce these. To maximize the energy savings, a hydraulic transformer is included in this approach. By coupling the inner and outer boom, potential energy is utilized for contrary motions of these. The developed algorithm for optimizing the energy demand is implemented in a holistic simulation model of a forestry crane arm. The eectiveness of this approach is tested in the model using representative trajectories. Energy savings of up to 26.9 % compared to a least norm pseudoinverse solution can be determined using the optimized control system. When the energy-saving potential of the coupling of the inner and outer boom is also considered, the total reduction in energy increases to up to 31.8 %.
  • Tesis de maestría
    Automation and optimization of agricultural soil tillage applying machine learning based on machine- and process sensor systems
    (2021) Kazenwadel, Benjamin; Geimer, Marcus; Stein, Alexander; Becker, Simon
    Climate change and cost pressure lead to new environmental and economic challenges that increase the demand for innovative control systems to automate and optimize agricultural tasks. Automating speed control during power-intensive soil tillage can increase eciency and sustainability and counteract the lack of qualied personnel in agriculture. A survey was carried out focused on tillage by cultivating to obtain an overview of the challenges farmers face during their work, including their target preferences. Based on the obtained requirements for tillage by cultivating, a system was developed automating working depth control by online Lidar plane detection to ensure tillage quality and establish a basis for good plant growth. Automated speed control is realized based on an online-parameterized draft force and traction model combined with the usage of a neural network for fuel rate prediction. The network is trained oine and adaptable to the individual preferences of the farms and varying implements. Thereby, the operator can choose and customize optimization objectives such as fuel eciency, performance, or total cost. During the evaluation, the control system was tested with various objectives against a human driver and was able to perform optimization on the individual objective. Furthermore, the transferability of the system was demonstrated with the usage of another implement.
  • Tesis de maestría
    Optimization of the organic Rankine cycle power plant MoNiKa's control system
    (2021-02-08) Gutiérrez Guerra, Juan Francisco; Wiemer, Hans-Joachim; Nemirovsky, Nicolás
    ENG: The aim of this work was to optimize the MoNiKa organic Rankine cycle power plant control system. In particular, performance and robustness of the PID control loops were evaluated for the main and support feed pumps and throttling valve. Each component was physically modelled in Simscape, while control simulations were performed in Simulink based on process transfer functions. The tuning methods were chosen in order to achieve faster, more robust responses to setpoint and disturbances changes. Stability, sensitivity and settling time values were calculated on MATLAB based on frequency response techniques, and results were compared with a set of previously measured data. Final results showed that, using the Continuous Cycling Method, the optimized controllers’ parameters were able to provide a better setpoint tracking and disturbance rejection, while accomplishing up to 10 times faster responses than the preliminary PID controllers’ settings. SPA: El objetivo de este trabajo fue optimizar el sistema de control del ciclo orgánico Rankine de potencia MoNiKa. En particular, se evaluó el desempeño y robustez de los lazos de control PID de las bombas principal y de soporte y de la válvula de estrangulación. Los componentes fueron modelados en Simscape, mientras que las simulaciones de los sistemas de control se ejecutaron en Simulink, en base a funciones de transferencia. Los métodos de ajuste fueron seleccionados para brindar respuestas más rápidas y robustas ante cambios de setpoint y perturbaciones. Valores de estabilidad, sensibilidad y tiempo de asentamiento fueron calculados en MATLAB en base a técnicas de respuesta en frecuencia, y los resultados fueron comparados con un conjunto de mediciones previamente tomadas. Los resultados finales demostraron que, usando el Método de Ciclo Continuo, los parámetros optimizados lograron un mejor seguimiento de setpoint, mejor rechazo a perturbaciones y respuestas hasta 10 veces más rápidas que los parámetros preliminares.