1,721,010 research outputs found
Modellazione multiscala di celle a combustibile ad ossidi solidi: dalla microstruttura alle prestazioni
No full textIn questo studio si presenta un approccio modellistico integrato per la simulazione di celle a combustibile ad ossidi solidi (SOFC). La modellazione copre in primis gli aspetti microstrutturali degli elettrodi porosi compositi costituenti la cella, le cui proprietà effettive di trasporto e reazione sono predette con la teoria di percolazione e/o con la ricostruzione numerica della microstruttura in funzione di composizione, distribuzione granulometrica delle polveri e condizioni di sinterizzazione. Le proprietà effettive costituiscono i parametri dei modelli di trasporto e reazione all'interno della cella, basati su bilanci di massa e carica, che permettono di ottenere la distribuzione delle variabili di campo e l'efficienza energetica del sistema. L'accoppiamento della modellazione microstrutturale con quella di trasporto e reazione permette di correlare i due livelli di scala cosicché i modelli tra loro integrati sono utilizzati come strumento interpretativo dei dati sperimentali e come strumento per l'ottimizzazione di prestazione e design.In this study an integrated modelling framework for the simulation of solid oxide fuel cells (SOFC) is presented. The modelling firstly covers the microstructural aspects of porous composite electrodes which constitute the cell, whose effective transport and reaction properties are predicted by means of percolation theory and/or numerical reconstruction of the microstructure as a function of composition, particle size distribution and sintering conditions. The effective properties are parameters of the models of transport and reaction within the cell, based on mass and charge conservation balances, which allow to obtain the field variables distribution and the energetic efficiency of the system. Coupling the microstructural modelling with the transport and reaction modelling enables the correlation of the two different scale levels, so that the integrated models are used as interpretative tool of experimental data as well as design tool for optimize the performance
Physically-based impedance simulation to decouple convoluted transport and reaction phenomena in SOFC cathodes
No full textA mechanistic model, based on mass and charge conservation equations [1], is presented for the physically-based simulation of impedance spectra in composite solid oxide fuel cell cathodes, taking into account the complex interaction between transport and reaction phenomena. The impedance simulation, which reproduces the same procedure used in laboratory frequency response analyzers, allows the de-convolution of distinct elementary processes and the identification of a specific double layer chemical capacitance, describing the possible accumulation of adsorbed species and reaction intermediates at the interface between electron-conducting and ion-conducting particles. The satisfactory agreement of simulated spectra with experimental data for different operating conditions and electrode thicknesses reveals that the model is capable to reproduce the transient behavior of composite electrodes by relying on only one fitted parameter. Model simulations show that mass-transfer processes within the electrode produce a resistive contribution in the impedance spectra related to the effect of the local oxygen partial pressure on the reaction kinetics. In addition, the pores act as a buffer for molecular oxygen, leading to a capacitive contribution in the frequency range 10^2-10^4Hz, more pronounced at high current densities
Microstructural modelling for prediction of effective properties in porous SOFC electrodes
No full textA modelling framework for the prediction of effective properties in porous SOFC electrodes is presented. The model consists of: i) a packing algorithm to numerically reconstruct the microstructure, and ii) a Monte Carlo method to calculate the effective transport properties. This modelling technique improves the accuracy of the prediction of effective properties beyond percolation theory estimates. In addition, the numerical reconstruction does not rely on existing samples and complex instrumentations (for example, X-ray tomography, FIB-SEM analyses) required by other reconstruction methods.
The packing algorithm enables to numerically generate a representative sample of the electrode microstructure with the desired particle size distribution, composition and porosity. Sintering phenomena are simulated by increasing the overlap among the particles, pore-former particles are accounted for during the packing generation [1]. The model is capable to simulate packings of spherical particles as well as of agglomerates of spheres.
The reconstructed samples are then analyzed with a Monte Carlo method [2]. Random walk simulations are used to determine the transport properties in gas and solid phase, such as the effective diffusivity and the effective electric conductivity. Other geometric quantities can be evaluated, such as the pore size distribution, the surface area exposed to the gas phase, the three-phase boundary length.
In this study, effective properties as a function of porosity and particle size for random packings of spherical particles are calculated. The results are compared with independent experimental data, revealing a good agreement for both gas and solid phase properties. Effective properties of agglomerates of particles are also presented and compared with the results obtained for spherical particles. The comparison highlights that particle agglomeration significantly increases the mean pore size while reducing the effective gas diffusivity and the specific surface area exposed to gas phase (Figure 1).
The presented modelling technique can be used to improve SOFC electrode design and to support the interpretation of experimental data
An integrated microstructural and electrochemical approach for cell-level modeling: the LSM-based Juelich cell
No full textThe typical weak point of existing SOFC cell-level models is the evaluation of the electrode effective properties, typically performed by using simple percolation models or by fitting the microstructural parameters on the polarization curves. In this study we present an integrated approach which incorporates a detailed microstructural modelling into the cell-level model. The three-dimensional microstructure of each porous layer is numerically reconstructed with packing algorithms for an accurate prediction of the effective properties [1]. The predicted effective properties are used in a two-dimensional electrochemical model, based on conservation equations written in continuum approach, describing transport and reaction phenomena within the cell.
The integrated approach allows the prediction of the polarization behaviour from the knowledge of operating conditions and powder characteristics, eliminating the need for empirical correlations and adjusted parameters. The simulation of a short stack (F-design) of planar LSM-based anode-supported cells, developed and tested by Forschungszentrum Jülich, shows that a quantitative agreement with experimental data is obtained without fitting any parameter [2]. Simulations show that at 800°C the activation resistance in the cathode functional layer is the main contribution to cell overpotential. In addition, gas concentration effects at the anode produce the parabolic shape of the polarization curve near OCV and lead to reduce the polarization resistance as the water molar fraction in the fuel stream increases
Erratum: A particle-based model for effective properties in infiltrated solid oxide fuel cell electrodes (Journal of the Electrochemical Society (2014) 161 (F1243))
No full textThis article was published online on September 11, 2014 before all of the corrections/changes the author requested had been made. ECS apologizes for these errors. The article was corrected online on September 15, 2014
GHG emissions in industrial activities: The role of technologies for their management and reduction
Full text linkTo deal with the problem of the Climate System Change and the Global Warming, countries as well industries require to decrease the amount of CO2 emissions released globally by developing greener technologies and improving the use of renewable energies. The role of the research, in particular process engineering, is to develop and demonstrate technologies in order to protect the world from the current deterioration situation, which could potentially develop more frequent natural disasters, raising in the sea level and cause harm to the human health and ecosystems. The Chemical Engineering group at Department of Civil and Industrial Engineering of Pisa University has been involved in several projects concerning carbon reduction and emission from energy production in different Sectors, in collaboration with public and private organizations and international networks. The research topics have been briefly reviewed and objectives for further studies have been identified
Control of 2-chlorophenol vapour emissions by a trickling biofilter
No full textThis research work investigates the biodegradation of 2-chlorophenol vapours in a trickling biofilter packed with a ceramic material, and seeded with a pure strain of Pseudomonas pickettii
The estimation of the solid size and density in fluidised-bed biological reactors
No full textThe method proposed by Akapo et al. (1989) for the estimation of porous solid densities and extended in this paper for the evaluation of density and size of composite materials fluidised by a liquid (as in the biological fluidised bed) has proved quite successful: for all the beds examined, experimental data on overall bed height vs fluidising flux have been sufficient for the estimation of the particle physical parameters
Blending recycled poly(lactic acid) (PLA) with elastane recovered from textile fibers: A sustainable valorization approach
No full textThe recycling of elastane from textile waste and its reintegration into polymeric matrices represents a possible pathway towards the achievement of a real circular economy in the textile industry. This study investigates the dissolution and recovery of elastane using environmentally friendly solvents and its subsequent blending with recycled poly(lactic acid) (PLA). Among tested solvents, dimethyl sulfoxide (DMSO) was the most effective, dissolving elastane at 120 °C with a solubility limit of 40.77 mg EL/g DMSO at 160 °C. Recovery via non-solvent induced phase separation (NIPS) allowed for 75–80 % solvent recovery, with residual DMSO reduced down to 5–6 % after drying. Blends of recycled PLA with recovered elastane (5–15 wt.%) were produced via melt extrusion and evaluated for mechanical and thermal properties. Tensile tests revealed that adding elastane reduced the elastic modulus (from 3.52 GPa for PLA to 3.14 GPa for PLA+15) while increasing elongation at break. However, tensile strength declined due to poor interfacial adhesion between PLA and elastane. Dynamic mechanical thermal analysis (DMTA) confirmed elastane's limited compatibility with PLA, showing separate glass transition temperatures at ∼60 °C (PLA) and ∼10 °C (elastane). Differential scanning calorimetry (DSC) indicated an increase in PLA crystallinity (from 19.5 % for PLA to 24.9 % for PLA+5), followed by stabilization around 20.7 % at higher elastane content. Scanning electron microscopy (SEM) revealed elastane dispersion within the PLA matrix, with droplet coalescence at higher elastane concentrations. Despite its limited compatibility, this study highlights the potential for elastane to have a second life and demonstrates the feasibility of incorporating it into recycled PLA. It lays the foundation for future research on compatibilization strategies to improve mechanical performance
Revitalizing Plastic Waste with Pyrolysis: a UniSim Design© Simulation Case study for Renewable Energy Production from Car Fluff
No full textThis study addresses the imperative of substituting fossil fuels with energy from wastes, focusing on car fluff pyrolysis. The environmental viability of fuels produced through this method is assessed, aligning with the European Union's Renewable Energy Directive II (RED II) emissions assessment methodology. Using UniSim Design©, the entire inventory for an industrial-scale process is modeled, examining emissions contributions from each facility. By repurposing automotive waste, waste reduction and renewable energy generation are simultaneously achieved, in line with RED II objectives. UniSim Design© optimizes the heat integration system, minimizing energy wastage and reducing reliance on external sources, thereby lowering associated greenhouse gas emissions. Therefore, this research not only meets sustainability goals and regulatory compliance but also ensures the long-term viability of the plant in a changing regulatory environment
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