655 research outputs found
Energia tra individuo e ambiente: percezione e comunicazione dei sistemi di conversione dell'energia.
No full textLa tendenza all’aumento dei consumi non sembra conoscere cambiamenti, anzi: il 20 luglio 2007 è stato registrato il picco storico di richiesta di potenza elettrica pari a 56’520 MW.
A questa continua e crescente richiesta di energia va sommata la sfida lanciata con il Protocollo di Kyoto per la riduzione delle emissioni di gas climalteranti e la necessità di garantire un sicuro approvvigionamento delle fonti. La risposta a queste esigenze, che non sono solo italiane, è stata individuata dalla politica nell’incremento dell’efficienza energetica, nell’incremento dell’utilizzo delle fonti rinnovabili e nell’utilizzo dei biocarburanti per l’autotrazione.
Alla luce di quanto scritto, si sono volute approfondire gli argomenti sopra riportati, mettendo in luce la stretta connessione tra energia, il suo utilizzo e il suo ruolo nella società, al fine di contribuire al dibattito, che deve essere obiettivo, su base
scientifica, senza pregiudiziali e valutando benefici e rischi evitando di incorrere nell’utilizzo di parole d’ordine preconfezionate
Il nuovo polo della geotermia a Pontegradella: banco prova per una progettazione partecipata?
No full textLa fonte geotermica rappresenta un'opportunità per il raggiungimento degli obiettivi europei di contenimento del riscaldamento globale e, in particolare per l'Italia, per la riduzione della dipendenza dall'estero per l'approvvigionamento energetico. L’opposizione sociale, generata da una mancanza di fiducia, è ad oggi riconosciuta come la principale barriera all'ingresso nel mercato dell’energia. Nella partecipazione la possibile soluzione
Development of an equilibrium model for the simulation of thermochemical gasification and application to agricultural residues
No full textThe recent crisis in Italian agriculture has forced operators to find new ways of deriving income from their activities. One of the most promising of these is the use of agricultural products and residues as an energy source. In particular, the exploitation of agricultural, industrial and forestry residues and byproducts can be a definite advantage in the generation of electrical and thermal energy. This is due to the fact that these materials need to be disposed of and, therefore represent cost, and can be then transformed into an opportunity for revenue.
Among the various technologies available for converting biomass into biofuels, thermochemical gasification appears to be the most suitable for the conversion of crop residues (corn and sunflower
stalks, rapeseed straw, etc.) as these are characterized by low humidity and a high C/N ratio. On the other hand, the operational problems encountered with current plant architectures, such as the blocking of the biomass flow in the reactor due to low-melting ash content, have limited the use of crop residues in gasification so far.
In this paper, a model for the simulation of the biomass thermochemical gasification process is presented. The model is based on a chemical equilibrium hypothesis, i.e. it is assumed that the chemical transformations inside the gasifier can be described by a series of equilibrium reactions independent of each other and, therefore, a precise relationship between products and reactants can be determined. The model is validated by a comparison with data from literature and a sensitivity analysis on process parameters is presented. Finally, the model is applied to the study of the reliability of the gasification of crop residues currently popular in Italy, both in terms of produced gas quality and quantity
Development of a Model for the Simulation of Organic Rankine Cycles Based on Group Contribution Techniques
No full textMany industrial sectors and applications are characterized by the availability of low enthalpy thermal sources with temperatures lower than 400 °C, such as the ones deriving from both industrial processes (e.g. combustion products from gas turbines and internal combustion engines, technological processes and cooling systems) and renewable sources (e.g. solar and geothermal energy). The usual systems for the conversion of thermal energy into mechanical and/or electrical energy work due to the high temperature difference available between the source (i.e., combustion products) and the sink (i.e., the ambient). The Organic Rankine Cycle (ORC) is a promising process for conversion of heat at low and medium temperature to electricity. An ORC system works like a Clausius-Rankine steam power plant but uses an organic working fluid instead of water. A certain challenge is the choice of the organic working fluid and of the particular design of the cycle. The process should have high thermal efficiency and allow a high coefficient of utilization of the available heat source. Moreover, the working fluid should fulfill safety criteria, it should be environmentally friendly, and allow low cost for the power plant. An important aspect for the choice of the working fluid is also the temperature of the available heat source, which can range from low (about 100 °C) to medium temperatures (about 350 °C). In this paper, a model for the simulation of Organic Rankine Cycles is presented. The model is based on thermodynamics tables for the calculation of fluid properties and the Lee-Kesler method for the calculation of specific heat. Six commonly used working fluids (propane, butane, benzene, toluene, R134a and R123) are considered. Both saturated and superheated cycles are evaluated. A sensitivity analysis of the main process parameters is performed. Finally, the model is applied to a micro gas turbine/ORC combined cycle. Copyright © 2011 by ASME
Evaluation of the Performance of a Sirocco Fan Driven by a Diesel Engine in Mist Sprayer Applications
No full textThe coupling of a sirocco fan, used to supply air to a mist sprayer, and a Diesel engine is studied in order to enhance the performance of the integrated system. In this case, the main problem for the correct design of the fan arises from the fact that it is not possible to define a priori the operating point. In fact, the rotational speed is not fixed as in the case of an electric motor driven fan, but is determined as an equilibrium of the power supplied by the engine and the power absorbed by the fan to recover the pressure drops of the mist sprayer system. In this paper, the experimental campaign performed to characterize the existent fans is presented. Moreover, the sprayer duct is characterized by using literature correlations and by performing numerical simulations. Then, the collected data are elaborated in order to scale the fans in order to enhance the performance of the system. Copyright © 2011 by ASME
Numerical Analyses of High Reynolds Number Flow of High Pressure Fuel Gas Through Rough Pipes
No full textIn this paper, a CFD commercial code is used to evaluate the pressure drop through a pipe in a stream of high pressure gas. Preliminarily, a grid sensitivity analysis is carried out by comparing CFD results with analytical results. Hybrid grids are generated starting by a tetrahedral mesh by adding prism layers on the surface of the pipe. Each grid is characterized by different number and thickness of the layers in order to investigate the behavior of the grid with respect to the boundary layer.
Then, the model based on the best performer grid is validated by using a literature test case, in which a high pressure gas flow through rough pipe is experimentally studied. Various equation of state (i.e. constant properties, ideal gas and Redlich Kwong equation) and boundary conditions (e.g. pressure, mass flow, etc.) are taken into consideration.
Finally, the model is used to extrapolate the behavior of different gas (i.e. natural gas, biogas and hydrogen-methane mixture) flowing at high pressure through pipe characterized by different roughness
Valutazione delle Prestazioni di un Ventilatore Sirocco Trascinato da un Motore Diesel in Macchine Atomizzatrici
No full textIn questo lavoro viene studiato l'accoppiamento di un ventilatore radiale a pale in avanti del tipo Sirocco (a gabbia di scoiattolo), usato per alimentare una macchina atomizzatrice, con un motore diesel con lo scopo di migliorare le prestazioni del sistema integrato. In questo caso, il problema principale per la corretta progettazione del ventilatore deriva dal fatto che non è possibile definire a priori il punto di funzionamento. Infatti, la velocità di rotazione non è fissata, come è nel caso di un ventilatore azionato da un motore elettrico, ma è determinata dall'equilibrio tra la potenza erogata dal motore e la potenza assorbita dal ventilatore per fornire al fluido la potenza necessaria a recuperare le perdite di carico del sistema atomizzatore.
In questo lavoro viene presentata la campagna sperimentale effettuata per caratterizzare i ventilatori esistenti. Inoltre, il condotto dell'atomizzatore è caratterizzato mediante l'utilizzo di correlazioni di letteratura e simulazioni numeriche. Infine, i dati raccolti precedentemente vengono elaborati per scalare i ventilatori al fine di migliorare le prestazioni del sistema
Acoustic and Vibrational Analyses on a Multi-Stage Compressor for Unstable Behavior Precursor Identification
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