1,721,162 research outputs found
Improving the overall thermal performance of parabolic trough solar collectors using porous media
Full text linkIhe of use porous irsert constituted by a metal matrix of copper Raschig Rings is proposed here for parabolic trough solar collectors. The CFD analysis, based on a well-established numerical model, allows computing a significant increase in the thermal performance of the lube considered in the analysis, when equipped with the porous insert, with respect to a smooth pipe. The useful power grows up to -96 % of the absorbed incident power. A reduction of a factor of 5 in the radiative and convcctivc losses is computed, due to a large drop in the pipe surface temperature. The length of the porous insert, however, should be carefully evaluated in view of the significant additional pressure drop caused by the insert
Thermal-Hydraulic Analysis of the JT-60SA Central Solenoid Operation
Full text linkThe minimum temperature margin of the JT-60SA CS coil in the standard (pulsed) operation scenario, with 5.5 MA plasma current and 75 s flattop, is computed using the state-of-the-art 4C code for different values of the coupling time constant nτ. The margin is >1 K, provided nτ <130 ms
Optimization of the flow distribution in a gyrotron cavity using evolutionary CFD simulations driven by a genetic algorithm
Full text linkThe steadily increasing performance requested to gyrotrons, to comply with their function of heating and current drive in fusion reactors, put a progressively increasing burden on the heat removal from the interaction cavity, where the heat flux can easily reach 20 MW/m2 on its inner surface. The cavity is actively cooled by subcooled water in forced flow in an annular region, and the water flow typically enters and exits through a single inlet and outlet. The high-speed flow entering from the inlet potentially drives an inhomogeneous flow azimuthally in the cavity region, but helps in locally bursting the heat removal due to the impinging effect of the cold-water flow. Here a new design of the water inlet in the cavity region is performed through a simplified genetic algorithm, in such a way that the flow homogeneity in the gyrotron cavity is maximized, without reducing the beneficial cooling due to the impact of the water jet on the cavity wall. The presence of multiple holes feeding the cavity, with their azimuthal location driven by the genetic algorithm, is analyzed through Computational Fluid Dynamics (CFD) simulations. Once the multi-inlet location is optimized, the dimension of the inlet holes is tuned to burst the heat transfer effect, reaching a high level of temperature and flow homogeneity in the cavity
Numerical assessment of hydraulic properties of Triply Periodic Minimal Surfaces structures
No full textThe present work is devoted to evaluating the hydraulic properties of Triply Periodic Minimal Surfaces (TPMS) structures, a generation of porous structures developed using the periodicity of trigonometric equations to generate triply periodic minimal surfaces. The thorough computational and experimental analysis coupled with verification assessment is key to using these product structures in thermal hydraulics especially to address industrial requirements. Here the hydraulic properties are computed by performing three-dimensional CFD analyses using Star-CCM+. Gyroid TPMS was hydraulically analyzed with a water flow in three-channel configurations (circular, square, and rectangular section), with the same hydraulic diameter and length, respectively 5.08cm and 10cm. Their porosity values range from 80% to 93% depending on the unit cell dimensions (chosen values were 10mm, 15mm, 20mm, 25mm, and 30mm). The CFD models for the rectangular TPMS contain the maximum epistemic uncertainty of 19% following the ASME VV 20 codes. In preparation for the forthcoming test campaign, the hydraulic characteristic of the different channels is assessed comparatively, and the friction factors are computed and compared to reach a basic understanding of the parametric effect of channel shape and cell size
Might future electricity generation suffice to meet the global demand?
Full text linkElectricity supply is one of the critical issues in the energy field. Due to the high shares of greenhouse gases emissions, the electricity sector is experiencing a transition towards a progressively wider use of low-carbon technologies. At the same time, electrification of end-use sectors is identified as one of the most suitable mitigation strategies, although requiring larger electricity production. This paper relates the historical development trends for installed capacity of electricity production technologies to the theory of the S-curves, building a method to depict plausible developments in the electricity sector. Projections are performed considering the existence of an upper limit for industrial capacity development, and according to a path envisaging a revolutionary, an evolutionary and a maturity phase for technologies showing considerable growth trends. Oppositely, stagnation is taken into account for those not showing any remarkable progress. The computed curves are used to perform forecasts about electricity generation potentials until 2050, showing how the projected growth trend of electricity generation technologies would result in a production sufficient to meet the expected global demand, even excluding the contribution of fossil fuels in some cases. In perspective, the presented method can be applied to retrieve maximum capacity constraints for energy system models
Hydrodynamic characterization of Gyroid, Diamond and Split-P Triply Periodic Minimal Surfaces as porous medium
Full text linkTriply Periodic Minimal Surfaces are gaining significant attention as engineered porous media for applications in fluid transport and thermal management systems due to their unique geometric properties. However, accurate prediction of pressure drop across TPMS structures remains a challenge, particularly in transitioning flow regimes. This study addresses this gap by investigating the hydrodynamic behavior of Gyroid, Diamond, and Split-P geometries using computational fluid dynamics simulations across a range of Reynolds numbers, from viscous to weakly inertial regimes. Two modeling frameworks were utilized: the Ergun equation, commonly used for packed beds, and the Darcy-Forchheimer equation, enhanced with newly developed correlations for permeability and inertial drag factor. An adapted Kozeny-Carman equation was also applied for permeability prediction. The developed correlations, expressed as power-law functions of porosity and tortuosity, demonstrated high accuracy, with relative errors below 10 % for most configurations and a maximum error of 21 % for the more complex Split-P1 geometry. Validation in larger-scale geometries, such as pipes filled with TPMS, confirmed the scalability and robustness of the proposed models, even when accounting for variations in the hydraulic diameter due to wall effects. The results demonstrate the superior suitability of the Darcy-Forchheimer equation with the developed permeability and inertial drag factor models, particularly for complex geometries like Split-P. In contrast, the Ergun equation fails to accurately predict pressure drop across the investigated TPMS, underscoring its limitations for these geometries. Furthermore, while the inclusion of tortuosity in the correlations provides additional detail, it does not offer significant advantages over the simpler permeability-porosity relation for any of the investigated TPMS, making the latter a more practical choice for design and optimization applications in systems such as heat sinks and porous flow device
Recycling behaviour of italian citizens in connection with the clarity of on-pack labels. A bottom-up survey
Full text linkThe present work studies, through an online survey, the recycling behaviours of a representative sample of Italian end users, in connection with the effectiveness of on-pack recycling indications of different packed materials. The study has a special focus on the clarity of on-pack recycling indications to convey waste sorting information, and the impact of clear and straightforward labelling to improve the sorting result. The work took advantage of social media as the distribution platform, thus obtaining a relatively high involvement of citizens. To investigate the representativeness of the sample, some of its characteristics were subject to checks and comparisons to their corresponding values of the Italian population. According to almost three-quarters of the responders, a clear and straightforward labelling will improve the result of their waste sorting drastically. The general awareness of the answerers relative to the importance of waste recycling and willingness to improve the quality of their sorted waste is very high among the participants but the overall satisfaction of the on-pack indications is relatively low. The score of on-pack labels in conveying information on recycling and waste segregation is evaluated as improvable. A higher perception of circular economy concept leads to more re-utilisation of the packaging parts, which increases with the awareness about the importance of recycling
Analysis of the effects of electrification of the road transport sector on the possible penetration of nuclear fusion in the long-term european energy mix
Full text linkThe European Roadmap towards the production of electricity from nuclear fusion foresees the potential availability of nuclear fusion power plants (NFPPs) in the second half of this century. The possible penetration of that technology, typically addressed by using the global energy system EUROFusion TIMES Model (ETM), will depend, among other aspects, on its costs compared to those of the other available technologies for electricity production, and on the future electricity demand. This paper focuses on the ongoing electrification process of the transport sector, with special attention devoted to road transport. A survey on the present and forthcoming technologies, as foreseen by several manufacturers and other models, and an international vehicle database are taken into account to develop the new road transport module, then implemented and harmonized inside ETM. Following three different storylines, the computed results are presented in terms of the evolution of the road transport demand in the next decades, fleet composition and CO2emissions. The ETM results are in line with many other studies. On one hand, they highlight, for the European road transport energy consumption pattern, the need for dramatic changes in the transport market, if the most ambitious environmental goals are to be pursued. On the other hand, the results also show that NFPP adoption on a commercial scale could be justified within the current projection of the investment costs, if the deep penetration of electricity in the road transport sector also occurs
Design of a 10 MW/m2-heat-flux removal system for a W7-X divertor tile using triply periodic minimal surfaces
Full text linkIn nuclear fusion reactors, the heat removal from high-heat-flux components such as the divertor has always been a challenge as the heat flux is anticipated to easily overcome 10 MW/m2, as it is the case for the divertor tiles in the W7-X stellarator. In this paper a new cooling solution, relying on a Triply Periodic Minimal Surface lattice, is proposed and investigated. The analysis first focuses on the identification of the optimal lattice with a dedicated investigation on a reduced computational domain. The analysis with the best candidate is moved to a 30 cm × 10 cm divertor tile, to prove the compliance with the operating constraints. The tile with the gyroid lattice with unit cell size of 10 x 10 × 5 mm3 is shown to be capable to withstand a heat flux of 10 MW/m2, distributed over a heated length of 10 cm, when 1.25 kg/s of subcooled water are used for cooling, resulting in a pressure drop <0.6 MPa and tolerating a very limited fluid boiling just around the inlet/outlet manifolds. Eventually, the benefits of this configuration, when compared to others, in terms of enhancement of the performance and structure lightning, are discussed
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