196746 research outputs found
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Selection of pure and binary working fluids for high-temperature heat pumps: A financial approach
No full textHigh-temperature heat pumps are increasingly being recognized for decarbonizing industrial heat supply up to 200 °C. In the open literature, the operating conditions, working fluids and configurations of high-temperature heat pumps are typically optimized for achieving a maximum Coefficient of Performance (COP). This work however presents a method that optimizes the operating conditions, working fluid and configuration of the heat pump, based on a combined financial and technical appraisal. In this regard a financial model to calculate the levelized cost of heat (LCOH) of a heat pump unit is developed. The model screens a large set of working fluids and therefore allows for subcritical, transcritical and supercritical operation and includes (zeotropic) binary mixtures. The methodology is applied to a large set of generic temperature profiles, with process temperatures between 160 °C and 200 °C and heat source temperatures between 80 °C and 120 °C. The results indicate that designing a heat pump solely based on maximum COP may lead to a sub-optimal financial solution. Overall, binary mixtures, either zeotropic or azeotropic, of natural working fluids often performed best. The benefits of zeotropic mixtures are twofold: improved temperature matching and flexibility in their thermophysical properties. However, for industrial processes with high temperature glides, pure fluids operating in the transcritical regime proved to be the most promising. The study also highlights the sensitivity of the financial performance to the electricity price, annual operating hours and heating capacity
Design optimization of advanced tow-steered composites with manufacturing constraints
No full textTow steering technologies, such as automated fiber placement, enable the fabrication of composite laminates with curvilinear fiber, tow, or tape paths. Designers may therefore tailor tow orientations locally according to the expected local stress state within a structure, such that strong and stiff orientations of the tow are (for example) optimized to provide maximal mechanical benefit. Tow path optimization can be an effective tool in automating this design process, yet has a tendency to create complex designs that may be challenging to manufacture. In the context of tow steering, these complexities can manifest in defects such as tow wrinkling, gaps, overlaps. In this work, we implement manufacturing constraints within the tow path optimization formulation to restrict the minimum tow turning radius and the maximum density of gaps between and overlaps of tows. This is achieved by bounding the local value of the curl and divergence of the vector field associated with the tow orientations. The resulting local constraints are effectively enforced in the optimization framework through the Augmented Lagrangian method. The resulting optimization methodology is demonstrated by designing 2D and 3D structures with optimized tow orientation paths that maximize stiffness (minimize compliance) considering various levels of manufacturing restrictions. The optimized tow paths are shown to be structurally efficient and to respect imposed manufacturing constraints. As expected, the more geometrical complexity that can be achieved by the feedstock tow and placement technology, the higher the stiffness of the resulting optimized design
Eggshell membrane-derived electrocatalysts for water electrolysis
No full textGreen H2 (GH2) holds significant promise as a renewable energy resource, particularly for addressing escalating energy demands sustainably. The imperative for economically viable GH2 technologies, primarily via water electrolysis, has spurred extensive research into suitable electrocatalytic materials. ESM is typically considered a biowaste material obtained from eggs, which are among the most widely consumed foods both domestically and industrially. Many countries legally require the effective treatment of ESM before disposal to prevent environmental contamination. Therefore, we propose upcycling ESM as an electrocatalytic support, forming transition metal-based active sites through chemical and thermal treatment, followed by doping highly reactive Fe sites electrochemically. ESM’s nanofibrous morphology and porous structure confer catalytic advantages. X-ray photoelectron spectroscopy analysis reveals that certain chemical functional groups in the ESM are involved in the spontaneous electrochemical charge transfer and the adsorption of metal ions, contributing to the formation of metal nanoparticles. Furthermore, various anionic chemical elements such as P, O, N, and S, which originate from intrinsic ESM, can participate in electrocatalysis. The Fe sites electrochemically induced on the Ni and Co nanoparticle surfaces in the ESMs demonstrate excellent electrocatalytic activity and durability toward the oxygen and hydrogen evolution reactions, respectively. This study provides a strategy to utilize ESM as an electrocatalytic material for the development of commercially viable electrocatalysts to produce GH2 by transforming biowaste into value-added materials. Moreover, it promotes the investigation of the (electro)chemical functionalities of biomaterials and the correlation between their functions and electrocatalytic activities
Safe and sustainable by design strategies for multicomponent nanostructured materials:Learnings from industrially relevant case studies
No full textThe continuous improvement of the functionality of materials by modulating their physicochemical properties by design is key to innovation and market growth. Novel materials with an enhanced function are referred to as ‘advanced’, and they are often nano enabled and/or consisting of multiple components. Despite their improved performance compared to a conventional alternative, new functionalities also may induce new characteristics in hazard and exposure profiles, challenging the existing materials risk assessment frameworks in balancing performance, safety, and environmental impact.In the context of the European Union Chemicals Strategy for Sustainability, the Safe and Sustainable by Design (SSbD) concept developed. SSbD recommends the assessment of chemicals and materials from early innovation phases, when options are many and budget is low. To support innovators during early screening phases, a combination of New Approach Methodologies (NAMs), guided by Integrated Approaches to Testing and Assessment (IATA), can be of value for informed decision making, bringing the advantage of increasing the screening speed for a set of materials, avoiding unnecessary animal testing. In this thesis a series of selected methodologies were developed and were shown to be suitable for early screening phases i.e., from ideation to lab phase. Moreover, SSbD screening is demonstrated on the example of one case study, oxide-perovskites for automotive catalysts, with the scope of bridging scientific findings and decision making. Three case studies, all being advanced nano enabled materials consisting of multiple components, were chosen for testing the methodologies developed and/or adapted in this thesis: oxide-perovskites for automotive catalysts, quantum dots for LED screens and inorganic aerogel mats for buildings insulation.With respect to human safety, the inhalation route of exposure was on focus in the thesis, given its importance when dealing with nanomaterials. Two NAMs from an inhalation IATA were selected as potentially useful SSbD screening tools and their applicability to multicomponent nanostructured materials was verified. The NAMs are dynamic dissolution in lung simulant conditions and bioreactivity by abiotic assays. Transformation studies after exposure with lung simulant fluids were also performed for all oxide perovskites, using the two previously mentioned NAMs and a combination of analytical techniques. Oxide-perovskites fate and effects in the lungs were found to be dependent on their multicomponent character which ultimately influence their electronic properties. Moreover, oxide-perovskites transformation by in chemico NAMs was found to be in good agreement with the studies performed in vivo, further confirming the utility of NAMs in a SSbD context.In addition, dustiness measurements were performed so to allow for an exposure estimation for workers in occupational settings. For materials in powder form, measurements were performed by following the small rotating drum method; for materials not in powder form, like the inorganic aerogel mats, occupationally relevant mechanical treatments were simulated, and the aerosol released was measured. Simulation included cutting using an insulation knife, cutting using a circular saw and sanding. Despite inorganic aerogel mats superior thermal insulation capacity, the ranking in number of particles released was higher compared to a conventional marketed alternative. Moreover, the number of particles released was found to be dependent on the mechanical treatment, whereas SEM-EDX analysis indicated that particles generated by sanding or circular sawing shared similar size and morphology, despite the different coatings and manufacturing processes of the mats.Regarding the environmental safety dimension, methods to measure dissolution and dispersion stability in aquatic media were developed and/or tested. For dispersible materials with medium to slow dissolution kinetics, the dispersion loading method offered higher precision in the rate constant determination. When dealing with fast dissolving materials, loading the material as a powder allows to deposit the material in a single layer on the filter, preventing material’s dissolution/agglomeration in the time between dispersion and injection. Several factors affecting nanomaterials transformation were investigated on the example of the oxide-perovskite case study. These include the influence of natural organic matter on dissolution and dispersion stability, the effect of pH, ionic strength, and water hardness. All perovskites were characterized by low stability in dispersion. The addition of natural organic matter slightly improved their stability whereas high water hardness resulted in higher instability. A combination of NAMs to evaluate dissolution and dispersion stability, was found to be an alternative way to account for environmental safety in aquatic systems at early innovation stages, avoiding higher tier testing. The same NAMs were also useful to inform ecotoxicity testing, by differentiating particles from solutes and by estimating the particles size in a dispersion.Lastly, concepts of similarities were explored for the comparison of NAMs outcomes for different materials in a group. Pairwise analysis conducted property-by-property enables comparison and ranking of several SSbD versions and allows the development of targeted design principles. Similarity matrices were scaled for a biologically relevant range, defined by controls for a NAM, and representative test materials were used for method calibration and read across.Sustainability along the life cycle was addressed by a qualitative approach, identifying positive and negative impacts on the targets of the UN Sustainable Development Goals (SDGs) for the case studies under analysis.In the final demonstration chapter on SSbD screening, important trade-offs between safety, sustainability and performance were identified on the example of oxide-perovskites for automotive catalysts. A potential improvement in functionality, linked to a positively impacted SDG target, had to be balanced with a potential safety or circularity concern, linked to a negatively impacted SDG target. Specifically for the oxide-perovskites, SDG 11.6 (improve air quality to reduce environmental impact of cities) and SDG 12.2 (sustainable management and use of natural resources) were found to be respectively positively and negatively impacted. A decision on a more favourable oxide-perovskite version is made by balancing all SSbD dimensions and may vary depending on the experts evaluating the case and by the economic situation of a company. If a project gets funded, expert judgement combined with stakeholders’ input may be a way to take a transparent decision.In this respect, this thesis provides guidance to informed decision making at early innovation phases, on the example of case study materials, contributing to the transfer, development and testing of alternative methods, further positioning suitable tools in a SSbD context. The collected knowledge brings together regulatory advice, industry practice and academia recommendations, and should be most of interest for small to medium enterprises and start-ups, as they often do not have the possibility to gather several experts to take informed decisions.In a pre-regulatory context like it is SSbD, the final choice lays with innovators, therefore expert driven guidance is needed to help them making the most balanced decision as early as possible in the innovation process, preventing future issues for human health and the environment, and avoiding regrettable substitutions
The complementary role of energy system and power grid models:An analysis of the European energy transformation from a holistic perspective
No full textThis paper describes a novel method for coupling energy system models with grid-planning models. The commonly used scenario building process, based on a review of existing studies and expert discussions, was enhanced by the use and further development of an open-source energy system model. The results were processed using a regionalisation method to couple the energy system model results with a power grid planning model. A grid analysis was then performed to simulate the load on the extra-high-voltage grid to identify grid congestion. This novel model coupling approach improves the consistency and transparency of the scenario-building process and enhances the analysis of grid development planning. The method was tested at the European level in a use case study analysing energy flows between sectors and countries, as well as the utilisation of electricity grids. Two scenarios with different assumptions regarding green hydrogen imports are considered. The key results indicate a large-scale expansion of renewable energy, with 844 GW to 970 GW of wind capacity and 2,136 GW to 2,460 GW of PV capacity in Europe. Compared to 2020, the EU therefore needs a five-fold increase in wind capacity and up to a 17.8-fold increase in PV capacity. In addition, the electricity grid interconnection capacity in the EU must almost triple to around 200 GW. A detailed analysis of the extra-high-voltage grid in Central Europe shows massive congestion and grid expansion needs at the national level. Furthermore, a successful energy transition will significantly reduce Europe's dependence on energy imports for gas by 63% and oil by 83% compared with current levels.</p
Formal Methods for Distributed Computing in Future Railway Systems
No full textAdvanced train control systems, such as ERTMS-ETCS and its future successors, that aim to increase the degree of autonomy of train driving, are based on algorithms strongly based on communication between geographically distributed computational elements. The high standards of safety and availability of rail transportation also impose high standards of safety and availability of such systems. Adopting formal methods for the specification and verification of distributed control algorithms is crucial to ensuring compliance with these high standards. Previous editions of DisCoRail (2019, 2021 [7], 2022 [8]), that since 2021 are tracks of ISOLA, have discussed the intertwining of formal methods and distributed computing in the design and development of innovative train control systems, with a specific focus on techniques to assess safety or availability, such as model checking or quantitative evaluation. This year’s edition aims to repeat the success of previous DisCoRail editions by stimulating discussion on these issues among researchers and experts from industry and academia
A dynamical systems approach to WKB-methods:The simple turning point
No full textIn this paper, we revisit the classical linear turning point problem for the second order differential equation ε2x′′ + μ(t)x=0 with μ(0) = 0, μ′(0) ≠ 0 for 0 <ε<<1. Written as a first order system, t = 0 therefore corresponds to a turning point connecting hyperbolic and elliptic regimes. Our main result is that we provide an alternative approach to WBK that is based upon dynamical systems theory, including GSPT and blowup, and we bridge – perhaps for the first time – hyperbolic and elliptic theories of slow-fast systems. As an advantage, we only require finite smoothness of μ. The approach we develop will be useful in other singular perturbation problems with hyperbolic–to–elliptic turning points
Confinement effect of FeMOFs glass enhances the proton coupled electron transfer reaction for the organic pollutants polymerization toward sustainable water purification
No full textPolymerization-driven removal of pollutants in advanced oxidation processes (AOPs) offers a sustainable way for the simultaneous achievement of contamination abatement and resource recovery, supporting a low-carbon water purification approach. In this work, metal–organic frameworks (MOFs) glass complexes (g-ZIF-62@8) were used as a platform to enhance proton transfer through the confinement effect of nanopores, modulating proton coupled electron transfer (PCET) reaction to promote organic pollutant polymerization. The results show that the confinement effect of nanopores in ZIF-62 glass can significantly improve the proton and electron transfer behavior, the proton diffusion coefficient is increased by 4.9 times (2.91*10−3 to 1.43*10−2), the energy barrier of the PCET reaction can be reduced by 1.9 eV, and the reaction kinetic rate constant is increased from 0.0198 min−1 to 0.20118 min−1. Photogenerated holes and Fe(IV = O), as the main reactive oxygen species (ROS), undergo PCET reaction with Bisphenol A (BPA) to convert them into phenoxy radicals, which are then polymerized into macromolecular organic compounds. PCET with proton-electron synergy was identified as a key driver of pollutant polymerization. This enables low-carbon purification and organic carbon recovery in wastewater. Our work provides new insights into the application of confinement effects to enhance proton and electron behavior to regulate pollutant polymerization toward sustainable water purification
The effects of nutritional state, sex and body size on the marine migration behaviour of sea trout
No full textThe sea trout (anadromous brown trout Salmo trutta) displays extensive among-individual variation in marine migration behaviour. We studied the migration behaviour of 286 sea trout (27-89 cm) tagged with acoustic transmitters in the spring, in 7 populations located in 2 distinct marine fjord systems in Norway. We examined whether individual nutritional state, sex and body size influenced marine migration behaviour in terms of (1) the decision to migrate to the sea or remain resident in freshwater and/or estuarine habitats, (2) seasonal timing of sea entry, (3) duration of the marine residency and (4) migration distance at sea from the home river. Most sea trout were in a poor nutritional state in the spring prior to migration. Sea trout with low body condition factors and low plasma triglyceride levels were more likely to migrate to sea, and low triglyceride levels were also associated with earlier sea entry. Poor body condition also increased the probability of individuals remaining at sea longer and migrating further offshore compared to fish in better condition. Females were more likely to migrate to the sea than males. Larger fish were also more likely to migrate to the sea instead of remaining in freshwater and estuaries, and dispersed over greater distances from the river than smaller fish. In conclusion, this study documented general trends across multiple populations and showed that nutritional state, sex and body size influence important aspects of the marine migration behaviour of sea trout
Thermal performance attenuation characteristics of solar collector field in solar district heating system
No full textn centralized solar district heating systems, the optical performance attenuation of the solar collector field significantly impacts the system’s heating efficiency and economics. However, accurate lifecycle models for the optical performance attenuation of solar collector fields are still needed. In this paper, the attenuation patterns of transmittance, absorption, and emissivity are systematically established through accelerated attenuation tests and calculation models. Based on this, a lifecycle model for optical performance attenuation was developed using TRNSYS and applied to a centralized solar heating system in Langkazi, XiZang. The results indicate that low inlet temperatures and high flow rates reduce optical performance attenuation, with ultraviolet damage of the glass cover being the main cause of performance attenuation, accounting for 74.5 % of heat loss. A 15-year lifecycle analysis shows that performance attenuation in the solar collector field results in a 16.7 % reduction in effective heat collection, a decrease in the solar fraction from 66.1 % to 55.1 %, and a 32.4 % increase in auxiliary heat supply. Increasing the heating area or thermal storage to collection area ratio helps mitigate optical attenuation. Based on this, from the perspective of mitigating the attenuation of collection efficiency, the thermal storage to collection area ratio should exceed 0.2 m3/m2, and the solar fraction is recommended to be kept below 0.7. Additionally, considering optical attenuation, the levelized cost of heat increases by over 0.03 CNY/kWh when the thermal storage to collection area ratio exceeds 0.2 m3/m2. The results provide a methodological basis for more accurate design of the solar heating system