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Combined vs separate heat and power production - Primary energy comparison in high renewable share contexts
No full textNatural Gas Combined Cycle (NGCC) units are currently the most efficient power plants based on fossil fuels. When used for Combined Heat and Power (CHP) production, serving District Heating (DH) systems, they have been usually promoted by stating their lower primary energy consumption compared to separate production of power and heat with conventional technologies. However, a significant increase of the share of Renewable Energy Sources (RES) in power generation and Heat Pumps (HP) for heat production in buildings could undermine this assumption. This paper evaluates a case study in Northern Italy, by comparing the real operation of three NGCC plants serving a DH network against the separate production of power (from real data of the National electricity mix) and heat (considering two scenarios based on natural gas boilers and heat pumps). The analysis is performed on hourly data over a two-years' time frame, to highlight the variations across the hours of the day and the seasons. To perform a comprehensive analysis, the entire system performance is considered, by comparing the useful energy supplied to the users to the primary energy consumption. The results show how the primary energy savings of fossil CHP technologies are strongly related with the available alternatives, which have been going through a significant evolution in last years. The separate production of heat and power can now be performed with competitive technologies, which benefit from the high share of RES in electricity production. Therefore, the comparison between combined and separate production is influenced by the high variability of the electricity generation mix, which needs to be carefully considered
Life cycle assessment of flame retardant cotton textiles with optimized end-of-life phase
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Wind Turbine Sliding Mode Control and Wind Farm Energy Optimization with Fatigue Constraints
No full textAxial crushing of metal-composite hybrid tubes: experimental analysis
Full text linkIn the automotive sector, special attention is paid to the study of the behavior of the structural components that make the car bodies. The continuous demands on the weight saving imply the car bodies to be assembled with components made in different materials and using different manufacturing processes. Considering the making of the sacrificial structures aimed to the energy absorption, composite materials are increasingly used to replace conventional metal materials. However, the use of composites is accompanied with a change in the type of deformation obtained during the impact phenomenon. Usually, with the conventional metal materials, the crushing behavior is a progressive buckling whereas the composite materials are characterized by a brittle fracture. The combination of the traditional metal materials with the composite ones can represent a good solution to obtain high levels of performance. In this context, the structural performance of metal-composite hybrid tubes subjected to quasi-static axial crushing is experimentally evaluated in this work. The specimens, with circular cross section, were obtained with tubes made in a fully thermoplastic composite internally reinforced with aluminum tubes. The composite material used were made in polypropylene both for the matrix and for the reinforcing fibers. This material has a good axial absorption capacity but irregular behavior during crushing. The addition of a conventional material as reinforcement allowed to increase the absorption capacity by ensuring a more progressive and controlled crush. The analysis was carried out by evaluating, for various geometric configurations, different parameters (mean load, average stress, specific energy, efficiency). The results, discussed in the work, showed how the energy absorption performance of a hybrid structure are higher than the sum of the performance of the single materials
APPLICATIONS OF BUILDING INSULATION PRODUCTS BASED ON NATURAL WOOL AND HEMP FIBERS
No full textFITNESs, Fibre Tessili Naturali per l'Edilizia Sostenibile (Natural Textile Fibers for Sustainable Building), is a research project concerning an experimental hemp and sheep wool insulation panel. The new panel has two main innovative features: unlike the already existing hemp and wool insulation mats, it is a semi-rigid product and has low environmental impact, as shown by the Life Cycle Assessment. FITNESs panels are particularly suitable for eco-building sector, as they are 100% natural, recyclable and made with by-products from local production chains (Piemonte Region). The paper presents the production process of the panel from wool and hemp fibers and some experimental applications for sustainable architecture
Separation and identification of structural modes in largely underdetermined scenarios using frequency banding
No full textIn recent years, blind source separation (BSS) has gained significant interest in the context of operational modal analysis, as a non-parametric alternative to the identification of mechanical structures from output-only measurements. One persisting limitation of most BSS methods, however, is to they cannot identify more active modes than the number of simultaneously measured outputs. The aim of this work is to propose a solution to the largely underdetermined case - where many more modes are to be identified than the number of available measurements -- by dividing the frequency axis in subbands, such that each band provides an (over)determined problem where BSS can be applied separately. The approach comes with the proposal of a new second-order BSS that operates directly in the frequency domain and takes as an input the cross-spectral matrix of the data. A data augmentation technique is also devised to artificially increase the dimension of the measurements in severely undetermined scenarios. Finally, an identification algorithm is introduced that estimates the modal parameters of the separated structural modes. A remarkable aspect of these algorithms is that they are all based on the unified use of multi-filters designed in the frequency domain, yet with different frequency bandwidths. Another particularity of the present paper is to demonstrate the validity of the proposed approach on several benchmark databases with various degrees of difficulty including complex modes, high modal overlap, singular modes, and the presence of engine harmonics. In all cases, the proposed methodology was efficient and, above all, easy to deal with even in largely undetermined cases
Unreal perpetual motion machine, Rydberg constant and Carnot non-unitary efficiency as a consequence of the atomic irreversibility
No full textA perpetual motion machine is a completely ideal engine which cannot be realized. Carnot introduced the concept of the ideal engine which operates on a completely reversible cycle, without any dissipation, but with an upper limit in it. So, even in ideal condition without any dissipation, there is something that prevents the conversion of all the energy absorbed by an ideal reservoir into work. But what is the cause of irreversibility? Here we highlight the atomic nature of this irreversibility, proving that it is no more than the continuous interaction of the atoms with the surrounding field. The macroscopic irreversibility is the consequence of the microscopic irreversibility
Combinatorial presentation of multidimensional persistent homology
No full textA multifiltration is a functor indexed by N^r that maps any morphism to a monomorphism. The goal of this paper is to describe in an explicit and combinatorial way the natural N^r-graded R[x_1,...,x_r]-module structure on the homology of a multifiltration of simplicial complexes. To do that we study multifiltrations of sets and R-modules. We prove in particular that the N^r-graded R[x_1,...,x_r]-modules that can occur as R-spans of multifiltrations of sets are the direct sums of monomial ideals