1,721,056 research outputs found
Analysis and comparison of different thermal cycles for power generation in space
No full textThis paper presents an analysis of solar-heat driven Brayton and Rankine power cycles operating in space with different working fluids. State of the art literature show that generation of power in space for terrestrial use can represent a great opportunity in the future for many reasons, including the facts that (1) the lowtemperature of space, - 3K, which acts as the power system heat sink, allows the attainment of very high efficiency even with low-temperature heat inputs, and (2) the solar energy input is higher than on earth, all this while using traditional cycles. This study is focused on analysis and comparison of performance of advanced Brayton and Rankine cycles operating under space conditions, with a main objective to advance the identification of system configurations, working fluids and conditions leading to the design of space power systems that combine high efficiency and low weight. Starting from previous studies that show the potential high efficiency of the use of diatomic gases (H2, N2) in regenerative Brayton and Rankine cycles we have presented a comparative analysis of different and more advanced Brayton and Rankine configurations to advance the understanding of the optimal trade-off between high efficiency (thermal and exergetic) and the smallest needed heat rejection exchanger area. The effect of the main cycles' operational parameters such as pressure ratio, turbine inlet temperature, working fluid mixture and different plant layouts on thermal and exergy efficiency and power to radiator area ratio have been analyzed. Under the examined conditions the thermal efficiency of regenerative - reheated-intercooled Brayton, that resulted being the best Brayton choice, reaches 71.8% while the efficiency of the reheated-regenerative Rankine cycle reaches 88.9%, both significantly higher than the previously analysed cycles taken as reference. The power/(radiator area) ratio, however, was an order of magnitude higher for the reheated-intercooled Brayton cycle, which may lead to lower costs of the generated power. This ratio was also found to increase with the introduction of reheating for both the Rankine and Brayton cycles, while the Interceding was in all cases disadvantageous
Modelling and simulation of a hybrid SOFC/GT system for an aircraft auxiliary power unit
No full textModeling and simulation of a hybrid PV/Thermal collector
No full textThe paper presents the simulation and analysis of an hybrid PV/Thermal solar collector, a combination of photovoltaic (PV) and solar thermal systems for the simultaneous production of electricity and heat from one integrated component. It is well known that the efficiency of a photovoltaic solar cell is adversely affected if the panel temperature exceeds the design value (typically, a loss of 0.5% results per degree in excess). This led to the idea of constructing a hybrid solar panel in which a coolant circulating on the bottom side of the photovoltaic cells (their non-irradiated side) allows to lower their operating temperature, thereby increasing both their efficiency and their life. The sensible heat of this coolant can be then recovered by generating domestic hot water or contributing to space heating. The plate-and-tube, water cooled PVT analysed in this work is the one that currently displays the most promising market perspectives. It consists of a glass plate, a photovoltaic panel, a metal plate welded on the backside and thin parallel tubes for the circulation of the cooling fluid. The model presented here is based on macroscopic mass-and energy balances of the individual components of the collector, allowing to calculate its electrical output and the outlet water temperature as a function of local solar irradiation and panel geometry data. The thermodynamic model of the PV/Thermal collector has been implemented in the library of a modular object-oriented Process Simulator, Camel-ProTM and the exergetic performance of the systems has been analyzed and compared with the performance of photovoltaic and thermal solar panel. A detailed analysis of the exergy destruction at component level is also presented, to better assess the distribution of irreversibilities across the process and to gain useful design insight
Analysis and comparison of solar-heat driven Stirling, Brayton and Rankine cycles for space power generation
No full textFeasibility analysis of a small-scale ORC energy recovery system for vehicular application
No full textThis paper analyses the feasibility of an "on-board" innovative and patented ORC recovery system. The vehicle thermal source can be either a typical diesel engine (1400 cc) or a small gas turbine set (15-30 kW). The sensible heat recovered from the exhaust gases feeds the energy recovery system that can produce sufficient extra power to sustain the conditioning system and other auxiliaries. The concept is suitable for all types of thermally propelled vehicles, but it is studied here for automotive applications. The characteristics of the organic cycle-based recovery system are discussed, and a preliminary design of the main components, such as the heat recovery exchanger, the evaporator and the pre-heater is presented. The main challenge are the imposed size and weight limitations that require a particular design for this compact recovery system. A possible system layout is analyzed and the requirements for a prototypal application are investigated. (C) 2014 Elsevier Ltd. All rights reserved
Thermoeconomic comparison of single and dual loop ORC for industrial waste heat recovery
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An application of the proper orthogonal decomposition method to the thermo-economic optimization of a dual pressure, combined cycle powerplant
No full textThis paper presents a thermo-economic optimization of a combined cycle power plant obtained via the Proper Orthogonal Decomposition-Radial Basis Functions (POD-RBF) procedure. POD, also known as "Karhunen-Loewe decomposition" or as "Method of Snapshots" is a powerful mathematical method for the low-order approximation of highly dimensional processes for which a set of initial data is known in the form of a discrete and finite set of experimental (or simulated) data: the procedure consists in constructing an approximated representation of a matricial operator that optimally "represents" the original data set on the basis of the eigenvalues and eigenvectors of the properly re-assembled data set. By combining POD and RBF it is possible to construct, by interpolation, a functional (parametric) approximation of such a representation. In this paper the set of starting data for the POD-RBF procedure has been obtained by the CAMEL-ProTM process simulator. The proposed procedure does not require the generation of a complete simulated set of results at each iteration step of the optimization, because POD constructs a very accurate approximation to the function described by a relatively small number of initial simulations, and thus "new" points in design space can be extrapolated without recurring to additional and expensive process simulations. Thus, the often taxing computational effort needed to iteratively generate numerical process simulations of incrementally different configurations is substantially reduced by replacing much of it by easy-to-perform matrix operations. The object of the study was a fossil-fuelled, combined cycle powerplant of nameplate power Pel=160MW, for which a set of operational and costing data was available: different combinations of the relevant process parameters were considered and the corresponding process variables calculated for each simulation were collected. In our case the aim of the application of the procedure was to find the combination of process parameters which corresponds to the minimum the thermo-economic cost of the products. The results obtained by the application of this model have been validated by comparison with literature data obtained by the application of genetic algorithm optimization
Modello 3D di celle a combustibile ad ossidi solidi alimentate da miscele di idrogeno e monossido di carbonio.
No full textAn exergy based method for the optimal integration of a building and its heating plant. Part 1: comparison of domestic heating systems based on renewable sources
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