04 Fakultät Energie-, Verfahrens- und Biotechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5
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Item Open Access Multi-criteria comparison of energy and environmental assessment approaches for the example of cooling towers(2022) Wenzel, Paula M.; Radgen, PeterCooling towers remove economically or technically unusable heat using considerable amounts of electricity and, in many cases, water. Several approaches, which vary in methodology, scope, and level of detail, are used for environmental evaluations of these cooling systems. Although the chosen approach has a significant impact on decisions made at the plant level, no methodology has yet been standardized for selecting the approach that best serves the objectives of the evaluation. Thus, this paper provides comparison criteria for the systematic selection of suitable evaluation methods for cooling towers and classifies how the methods score in this respect. These criteria, such as ‘life cycle thinking’, ‘inventoried physical quantities’, ‘temporal resolution’, ‘formalization’, and ‘data availability’, are grouped by overall evaluation objectives such as ‘thoroughness’, ‘scientific soundness’, and ‘usability’. Subsequently, these criteria were used to compare material flow analysis, energy analysis, environmental network analysis, life cycle inventory, life cycle assessment, environmental footprint methods, emergy analysis, exergy analysis, and the physical optimum method. In conclusion, material flow analysis is best suited for the analysis of cooling towers when impact assessment is not required; otherwise, life cycle assessment meets most of the defined criteria. Moreover, only exergy-based methods allow for the inclusion of volatile ambient conditions.Item Open Access Anti-adhesive surfaces inspired by bee mandible surfaces(2023) Saccardi, Leonie; Schiebl, Jonas; Balluff, Franz; Christ, Ulrich; Gorb, Stanislav N.; Kovalev, Alexander; Schwarz, OliverPropolis, a naturally sticky substance used by bees to secure their hives and protect the colony from pathogens, presents a fascinating challenge. Despite its adhesive nature, honeybees adeptly handle propolis with their mandibles. Previous research has shown a combination of an anti-adhesive fluid layer and scale-like microstructures on the inner surface of bee mandibles. Our aim was to deepen our understanding of how surface energy and microstructure influence the reduction in adhesion for challenging substances like propolis. To achieve this, we devised surfaces inspired by the intricate microstructure of bee mandibles, employing diverse techniques including roughening steel surfaces, creating lacquer structures using Bénard cells, and moulding resin surfaces with hexagonal patterns. These approaches generated patterns that mimicked the bee mandible structure to varying degrees. Subsequently, we assessed the adhesion of propolis on these bioinspired structured substrates. Our findings revealed that on rough steel and resin surfaces structured with hexagonal dimples, propolis adhesion was significantly reduced by over 40% compared to unstructured control surfaces. However, in the case of the lacquer surface patterned with Bénard cells, we did not observe a significant reduction in adhesion.Item Open Access Miscibility and phase separation in PMMA/SAN blends investigated by nanoscale AFM-IR(2021) Resch, Julia; Dreier, Julia; Bonten, Christian; Kreutzbruck, MarcItem Open Access Discussing the actual impact of optimizing cost and GHG emission minimal charging of electric vehicles in distributed energy systems(2021) Schulz, Maximilian; Hufendiek, KaiElectric vehicles represent a promising opportunity to achieve greenhouse gas (GHG) reduction targets in the transport sector. Integrating them comprehensively into the energy System requires smart control strategies for the charging processes. In this paper we concentrate on charging processes at the end users home. From the perspective of an end user, optimizing of charging electric vehicles might strive for different targets: cost minimization of power purchase for the individual household or - as proposed more often recently - minimization of GHG emissions. These targets are sometimes competing and cannot generally be achieved at the same time as the results show. In this paper, we present approaches of considering these targets by controlling charging processes at the end users home. We investigate the influence of differently designed optimizing charging strategies for this purpose, considering the electrical purchase cost as well as the GHG emissions and compare them with the conventional uncontrolled charging strategy using the example of a representative household of a single family. Therefore, we assumed a detailed trip profile of such a household equipped with a local generation and storage system at the same time. We implemented the mentioned strategies and compare the results concerning effects on annual GHG emissions and annual energy purchase costs of the household. Regarding GHG emissions we apply a recently proposed approach by other authors based on hourly emission factors. We discuss the effectivity of this approach and derive, that there is hardly no real impact on actual GHG emissions in the overall system. As incorporating this GHG target into the objective function increases cost, we appraise such theoretical GHG target therefore counterproductive. In conclusion, we would thus like to appeal for dynamic electricity prices for decentralised energy systems, leading at the same time to cost efficient charging of electric vehicles unfolding clear incentives for end users, which is GHG friendly at the end.Item Open Access Optimizing mass transfer in multiphase fermentation : the role of drag models and physical conditions(2023) Mast, Yannic; Wild, Moritz; Takors, RalfDetailed knowledge of the flow characteristics, bubble movement, and mass transfer is a prerequisite for the proper design of multiphase bioreactors. Often, mechanistic spatiotemporal models and computational fluid dynamics, which intrinsically require computationally demanding analysis of local interfacial forces, are applied. Typically, such approaches use volumetric mass-transfer coefficient (kLa) models, which have demonstrated their predictive power in water systems. However, are the related results transferrable to multiphase fermentations with different physicochemical properties? This is crucial for the proper design of biotechnological processes. Accordingly, this study investigated a given set of mass transfer data to characterize the fermentation conditions. To prevent time-consuming simulations, computational efforts were reduced using a force balance stationary 0-dimension model. Therefore, a competing set of drag models covering different mechanistic assumptions could be evaluated. The simplified approach of disregarding fluid movement provided reliable results and outlined the need to identify the liquid diffusion coefficients in fermentation media. To predict the rising bubble velocities uB, the models considering the Morton number (Mo) showed superiority. The mass transfer coefficient kL was best described using the well-known Higbie approach. Taken together, the gas hold-up, specific surface area, and integral mass transfer could be accurately predicted.Item Open Access Assessing fatigue life cycles of material X10CrMoVNb9-1 through a combination of experimental and finite element analysis(2023) Rahim, Mohammad Ridzwan Bin Abd; Schmauder, Siegfried; Manurung, Yupiter H. P.; Binkele, Peter; Dusza, Ján; Csanádi, Tamás; Ahmad, Meor Iqram Meor; Mat, Muhd Faiz; Dogahe, Kiarash JamaliThis paper uses a two-scale material modeling approach to investigate fatigue crack initiation and propagation of the material X10CrMoVNb9-1 (P91) under cyclic loading at room temperature. The Voronoi tessellation method was implemented to generate an artificial microstructure model at the microstructure level, and then, the finite element (FE) method was applied to identify different stress distributions. The stress distributions for multiple artificial microstructures was analyzed by using the physically based Tanaka-Mura model to estimate the number of cycles for crack initiation. Considering the prediction of macro-scale and long-term crack formation, the Paris law was utilized in this research. Experimental work on fatigue life with this material was performed, and good agreement was found with the results obtained in FE modeling. The number of cycles for fatigue crack propagation attains up to a maximum of 40% of the final fatigue lifetime with a typical value of 15% in many cases. This physically based two-scale technique significantly advances fatigue research, particularly in power plants, and paves the way for rapid and low-cost virtual material analysis and fatigue resistance analysis in the context of environmental fatigue applications.Item Open Access Dynamic monitoring of Frequency Containment Reserve activation(2021) Maucher, Philipp; Lens, HendrikFrequency Containment Reserve (FCR), also known as primary control reserve, is the fastest active power reserve (APR) used for system balancing. In the past, FCR was provided by a limited number of large units and the technical requirements on FCR activation could be monitored by a manual procedure. Due to the fact that FCR increasingly is provided by a large number of smaller units, manual procedures are no viable option for the future. For this reason, this article describes an automated concept for monitoring the quality of the activation of FCR during operation. Before FCR monitoring can be carried out, however, the measured active power has to be apportioned among the scheduled power and the different APR products, as they may be provided simultaneously. This article presents a method for the separation of different APR products based on dynamic models. In the proposed monitoring concept, a tolerance channel is created based on the FCR setpoint, defining the admissible range for FCR activation. This tolerance channel is established by means of a dynamic model corresponding to the slowest reserve provider (RP) whose FCR activation is still considered to be compliant. For the purpose of evaluation for longer time periods, the actual FCR activation is normalized relative to the tolerance channel. Finally, the article discusses results obtained with the proposed monitoring concept for different kinds of non-compliant FCR activation such as limited or delayed activation.Item Open Access Acid-base flow battery, based on reverse electrodialysis with bi-polar membranes : stack experiments(2020) Xia, Jiabing; Eigenberger, Gerhart; Strathmann, Heinrich; Nieken, UlrichNeutralization of acid and base to produce electricity in the process of reverse electrodialysis with bipolar membranes (REDBP) presents an interesting but until now fairly overlooked flow battery concept. Previously, we presented single-cell experiments, which explain the principle and discuss the potential of this process. In this contribution, we discuss experiments with REDBP stacks at lab scale, consisting of 5 to 20 repeating cell units. They demonstrate that the single-cell results can be extrapolated to respective stacks, although additional losses have to be considered. As in other flow battery stacks, losses by shunt currents through the parallel electrolyte feed/exit lines increases with the number of connected cell units, whereas the relative importance of electrode losses decreases with increasing cell number. Experimental results are presented with 1 mole L^-1 acid (HCl) and base (NaOH) for open circuit as well as for charge and discharge with up to 18 mA/cm2 current density. Measures to further increase the effciency of this novel flow battery concept are discussed.Item Open Access Strömungssimulation am IKE(1999) Becker, Sascha; Demuth, Rainer; Giese, Tobias; Heiken, Stefan; Niemann, Jens; Saptoadi, Dewanto; Laurien, EckartDie Simulation von Strömungen ist für die ingenieurmäßige Auslegung und die Sicherheitsanalyse von Energiesystemen, z.B. Kraftwerke, kern- oder klimatechnische Anlagen, von hoher Bedeutung. Die wachsende Relevanz des Forschungsgebietes Strömungssimulation in der Energietechnik wurde am Institut für Kernenergetik und Energiesysteme der Universität Stuttgart zum Anlaß genommen, die Abteilung Thermofluiddynamik zu gründen. Sie befaßt sich in Lehre und Forschung seit dem Sommer 1996 unter der Leitung von Prof. Dr.-Ing. E. Laurien mit der numerischen Simulation von Strömungen mit Wärmetransport und Turbulenz. Unter anderem werden Simulationen zweiphasiger Strömungen von z.B. Wasserdampf-Wasser oder Luft-Wasser durchgeführt. Von grosser Bedeutung sind hierbei Phasenaustauschvorgänge durch Schmelzen, Sieden und Kondensation, welche neben der numerischen Simu-lation von Blasenströmungen ein wichtiges Forschungsgebiet am IKE darstellen.Item Open Access Feasibility study on additive manufacturing of ferritic steels to meet mechanical properties of safety relevant forged parts(2022) Mally, Linda; Werz, Martin; Weihe, StefanAdditive manufacturing processes such as selective laser melting are rapidly gaining a foothold in safety-relevant areas of application such as powerplants or nuclear facilities. Special requirements apply to these applications. A certain material behavior must be guaranteed and the material must be approved for these applications. One of the biggest challenges here is the transfer of these already approved materials from conventional manufacturing processes to additive manufacturing. Ferritic steels that have been processed conventionally by forging, welding, casting, and bending are widely used in safety-relevant applications such as reactor pressure vessels, steam generators, valves, and piping. However, the use of ferritic steels for AM has been relatively little explored. In search of new materials for the SLM process, it is assumed that materials with good weldability are also additively processible. Therefore, the processability with SLM, the process behavior, and the achievable material properties of the weldable ferritic material 22NiMoCr3-7, which is currently used in nuclear facilities, are investigated. The material properties achieved in the SLM are compared with the conventionally forged material as it is used in state-of-the-art pressure water reactors. This study shows that the ferritic-bainitic steel 22NiMoCr3-7 is suitable for processing with SLM. Suitable process parameters were found with which density values > 99% were achieved. For the comparison of the two materials in this study, the microstructure, hardness values, and tensile strength were compared. By means of a specially adapted heat treatment method, the material properties of the printed material could be approximated to those of the original block material. In particular, the cooling medium/cooling method was adapted and the cooling rate reduced. The targeted ferritic-bainitic microstructure was achieved by this heat treatment. The main difference found between the two materials relates to the grain sizes present. For the forged material, the grain size distribution varies between very fine and slightly coarse grains. The grain size distribution in the printed material is more uniform and the grains are smaller overall. In general, it was difficult and only minimal possible to induce grain growth. As a result, the hardness values of the printed material are also slightly higher. The tensile strength could be approximated to that of the reference material up to 60 MPa. The approximation of the mechanical-technological properties is therefore deemed to be adequate.