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Nd-doped phosphate glass cane laser: From materials fabrication to power scaling tests
No full textWe report on the fabrication and characterization of two Nd-doped active glasses and two compatible cladding compositions. The materials were synthesized to be compatible in terms of thermal expansion and characteristic temperatures. The glass system with higher refractive index and absorption cross-section was selected for the fabrication of a core/cladding cane with a diameter of 800 mm. Laser experiments, performed on a 60 mm-long cane, show laser emission at 1054 nm with output power higher than 2 W and efficiency above 40%. These values, obtained on a very simple geometry, are promising for the development of short-length cane lasers and amplifiers for emission in the 1 micron region
DTT device: Conceptual design of the superconducting magnet system
No full textIn the European Fusion Roadmap, one of the main challenges to be faced is the risk mitigation related to the impossibility of directly extrapolate to DEMO the divertor solution adopted in ITER, due to the very large loads expected. Thus, a satellite experimental facility oriented toward the exploration of robust divertor solutions for power and particles exhaust and to the study of plasma-material interaction scaled to long pulse operation, is currently being designed. Clearly, design requirements for this experiment are quite challenging, to account for the extreme operation conditions, which shall be as representative as possible of the DEMO ones, but in a much smaller device and at lower costs. A feasibility assessment has been carried out for the fully superconducting magnet system of the compact Divertor Tokamak Test (DTT) facility project. The overall magnet system is based on NbTi and Nb3Sn Cable-in-Conduit Conductors, and it adopts some of the most recent developments in this field. It consists of 18 Toroidal Field (TF), 6 Poloidal Field (PF) and 6 Central Solenoid (CS) module coils. In order to cope with the machine requirements such as plasma major and minor radii, magnetic field on plasma axis, plasma current, and inductive flux requirement, the Nb3Sn TF coil is characterized by a peak field of 11.4 T on the conductor, operating at 46.3 kA; the Nb3Sn CS modules are characterized by a peak field of about 13 T, with a conductor operating current of 23 kA; the PF coils are wound using NbTi conductors operating at a maximum peak field of 4.0 T, with operating currents in the range 21 kA to 25 kA, depending on the PF coil. Profiting of the compact machine size, and thus of relatively short conductor lengths, the TF coil winding pack is conceived as layer wound and made of two distinct sections, a low- and a high-field one, employing different superconductor cross-sections, and electrically connected through an embedded "ENEA-type" joint. The main features of the magnet system are described here; the results of mechanical, electrical and thermohydraulic analyses, which are discussed here, indicate that the proposed design fulfills all the required criteria. In addition, a brief description of the In-Vessel coils is given, though they are not superconducting, for the sake of completeness
Sicurezza nei cantieri: analisi di rischio e condizioni di impiego di macchine operatrici e mezzi di sollevamento di materiali
No full textNel vasto quadro delle problematiche in materia di sicurezza nelle grandi opere di cantierizzazione, caratterizzate da alti livelli di meccanizzazione, la garanzia di adeguatezza delle macchine operatrici e delle attrezzature di sollevamento si pone certamente fra le esigenze prioritarie. La nota discute una tecnica di analisi e gestione del rischio coerente con le esigenze, logiche prima che normate, di rigore ed oggettività di analisi. Prendendo spunto da un approccio di provata efficacia, la tecnica consente di pervenire ad una verifica circa la sicurezza ed adeguatezza delle macchine allo impiego specifico, e può pertanto stabilire uno strumento utile agli analisti e ai tecnici degli Organi di Vigilanza, tanto in fase di scelte iniziali quanto in occasione di verifiche in corso d'opera. Un esempio di applicazione del metodo -seppure sviluppato per fronteggiare un problema contingente- conferma la validità generale della tecnica, a prescindere, come nel caso illustrato, dalla data di costruzione delle macchine in esame, e la sua efficacia anche quale riferimento per la identificazione di soluzioni di adeguamento realistiche e compatibili
Design of effective fins for fast PCM melting and solidification in shell-and-tube latent heat thermal energy storage through topology optimization
No full textThis paper presents a unique solution to the problem of heat transfer intensification in shell-and-tube latent heat thermal energy storage units by means of high conducting fins. We developed a design approach using topology optimization and multi-phase computational fluid dynamics. No assumption is made about the fins layout, which freely evolves along the optimization process resulting in more efficient non-trivial geometries. At each optimization iteration, the fluid-dynamic response in the phase change material is computed by solving the transient Navier-Stokes equations augmented with a phase-change porosity term. Coupling large design freedom to detailed physics modeling allowed studying the effect of convective transport on both design and performance of latent heat thermal storage units. Results indicate that accounting for fluid flow in design optimization studies is crucial for performance. It is shown that melting and solidification can be enhanced remarkably through natural convection by using well engineered fins with specific design features, that could hardly be revealed with alternative design routes. These features make designs optimized for melting fundamentally different from those optimized for solidification
Indirect contact pressure evaluation on pneumatic rod seals
No full textThis paper deals with the experimental evaluation of contact pressure at the interface between an elastomeric rod seal for pneumatic cylinders and its metallic counterpart without interposing any intrusive measuring device. A new test bench, which is able to measure the radial force exerted by a rod seal displaced at constant velocity on a sensorized portion of a cylinder rod over time, was designed and manufactured. The seal was pressurised to reproduce actual working conditions. A data postprocessing methodology was developed for an indirect evaluation of contact pressure starting from the experimental data set of the radial force exerted by the seal on the rod. At first, the measured radial force signal was filtered and properly fitted obtaining a differentiable function; then, contact pressure distribution was computed as a function of radial force time derivative, seal velocity and rod diameter. Preliminary experimental results are presented
The influence of microstructure on abrasive wear resistance of selected cemented carbide grades operating as cutting tools in dry and foam conditioned soil
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Mixed Virtual Elements for discrete fracture network simulations
No full textThe present work deals with the simulation of the flow in Discrete Fracture Networks (DFN), using the mixed formulation of the Virtual Element Method (VEM) on polygonal conforming meshes. The flexibility of the VEM in handling polygonal meshes is used to easily generate a conforming mesh even in the case of intricate DFNs. Mixed virtual elements of arbitrary polynomial accuracy are then used for the discretization of the velocity field. The well posedness of the resulting discrete problem is shown. Numerical results on simple problems are proposed to show convergence properties of the method with respect to known analytic solutions, whereas some tests on fairly complex networks are also reported showing its applicability and effectiveness
Deep geothermal exploration by means of electromagnetic methods: New insights from the Larderello geothermal field (Italy)
No full textThe main target of this research is the improvement of the knowledge on the deep structures of the Larderello-Travale geothermal field (Tuscany, Italy), with a focus on the Lago Boracifero sector, particularly on the heat source of the system, the tectonics and its relation with the hydrothermal circulation. In the frame of the PhD program and of the IMAGE project (Integrated Methods for Advanced Geothermal Exploration; EU FP7), we acquired new magnetotelluric (MT) and Time Domain EM (TDEM) data in a key sector of the field (Lago Boracifero). These data integrate the MT datasets previously acquired in the frame of exploration and scientific projects. This study is based also on a integrated modelling, which included and organized in Petrel (Schlumberger) environment, a large quantity of geological and geophysical data. We also propose an integrated approach to improve the reliability of the 2D MT inversion models, by using external information from the integrated model of the field as well as an innovative probabilistic analysis of the MT data. We present our attempt to treat the 1D magnetotelluric inverse problem with a probabilistic approach, by adopting the Particle Swarm Optimization (PSO), a heuristic method based on the concept of the adaptive behaviour to solve complex problems. The user-friendly software "GlobalEM" was implemented for the analysis and probabilistic optimization of MT data. The results from theoretical and measured MT data are promising, also for the possibility to implement different schemes of constrained optimization as well as joint optimization (e.g. MT and TDEM). The analysis of the a-posteriori distribution of the results can be of help to understand the reliability of the model. The 2D MT inversion models and the integrated study of the Larderello-Travale geothermal field improved the knowledge about the deep structures of the system, with a relevant impact on the conceptual geothermal model. In Micaschist and Gneiss complexes we observed a generally high electrical resistivity response locally interrupted by low resistivity anomalies that are well correlated with the most productive sectors of the field. A still partial melted igneous intrusion beneath the Lago Boracifero sector was detected based on the interpretation of the low resistivity anomalies located at a mid-crustal level (> 6 km). New insights on the tectonics are proposed in this research. The fundamental role of a large tectonic structure, i.e. the Cornia Fault, located along the homonymous river, was highlighted. In our opinion, this fault played an important role in the geothermal evolution of the Lago Boracifero sector, favouring both the hydrothermal circulation and the emplacement of magma bodies. In our opinion, the system can be ascribed to a "young convective and intrusive" field feed by a complex composite batholite
Dealing with fuel contaminants in biogas-fed solid oxide fuel cell (SOFC) and molten carbonate fuel cell (MCFC) plants: Degradation of catalytic and electro-catalytic active surfaces and related gas purification methods
No full textFuel cell and hydrogen technologies are re-gaining momentum in a number of sectors including industrial, tertiary and residential ones. Integrated biogas fuel cell plants in wastewater treatment plants and other bioenergy recovery plants are nowadays on the verge of becoming a clear opportunity for the market entry of high-temperature fuel cells in distributed generation (power production from a few kW to the MW scale). High-temperature fuel cell technologies like molten carbonate fuel cells (MCFCs) and solid oxide fuel cells (SOFCs) are especially fit to operate with carbon fuels due to their (direct or indirect) internal reforming capability. Especially, systems based on SOFC technology show the highest conversion efficiency of gaseous carbon fuels (e.g., natural gas, digester gas, and biomass-derived syngas) into electricity when compared to engines or gas turbines. Also, lower CO2 emissions and ultra-low emissions of atmospheric contaminants (SOX, CO, VOC, especially NOX) are generated per unit of electricity output. Nonetheless, stringent requirements apply regarding fuel purity. The presence of contaminants within the anode fuel stream, even at trace levels (sometimes ppb levels) can reduce the lifetime of key components like the fuel cell stack and reformer. In this work, we review the complex matrix (typology and amount) of different contaminants that is found in different biogas types (anaerobic digestion gas and landfill gas). We analyze the impact of contaminants on the fuel reformer and the SOFC stack to identify the threshold limits of the fuel cell system towards specific contaminants. Finally, technological solutions and related adsorbent materials to remove contaminants in a dedicated clean-up unit upstream of the fuel cell plant are also reviewed