1,721,325 research outputs found
A Criterion to Define Cross-Flow Fans Design Parameters
No full textThe paper presents an original criterion to parameterize systematically a cross-flow fan
configuration according to the most significant variables defining the geometry and then
affecting performance and efficiency. This choice of parameters has proved to be effective
in a systematic series of experimental tests aimed at investigating directions for design
improvement
A critical comparison between thermoeconomic and emergy analyses algebra
No full textBoth thermoeconomic accounting and emergy analysis methodologies deal with energy systems and are aimed at allocating costs of input resources among system products. They have, however, different goals and fields of application. The former focuses on energy systems converting the energy of fuel/s into the desired product/s. The latter amplifies the perspective by extending it to the wider level of biosphere, by including all the processes that are involved in the formation of system inputs, either devices or material and energy flows.
Differences and similarities in algebra are analyzed here with the aid of simple examples of single components having one or more inputs, outputs and feedbacks. Although some basic concepts of the two analyses may appear similar, they are indeed substantially different and lead to different and often not easily comparable results. Particular emphasis is given to the different idea of “conservation” that is behind the two analyses: while the exergy (or monetary) cost in the thermoeconomic analysis is conserved at component (and system) level, emergy is conserved along production streams according to the rules that are derived from the so-called memory algebra. Moreover, the paper shows the difficulty of the existing rules of the emergy algebra in dealing with splits that divide a flow of the same type into branches having different transformities, a case which was never considered before in the literature
A Global and a Local Approach with Evolutionary Algorithms to Locate Malfunction Causes in Energy Systems
No full textEnergy system performance may differ from the expected one during actual operation because of the effects of faults, anomalies, and wear and tear due to normal use. One of
the main issues of diagnosis, i.e., the procedure to discover the causes of malfunctions, is to find the way back from measured altered performance to the original cause. Several procedures were proposed in the literature to solve the diagnostic problem, usually based on the comparison between a reference nonmalfunctioning condition and an actual, possibly
malfunctioning, condition. A different strategy is suggested in the paper. A direct search of the possible causes of malfunctions is performed by means of an evolutionary algorithm: a component fault is arbitrarily introduced in a model of the healthy system by substituting the reference characteristic curve with an altered one, and the algorithm is used to search for a combination of different kinds of performance modifiers that generates the same measured effects of the actual anomaly. A global and a local approach are proposed and applied to a real test case plant, also in presence of measurement noise.
The local approach demonstrates to be more effective in terms of accuracy and computational
effort
High efficiency power generation from biomass sources using externally fired supercritical CO2 Brayton cycles
No full textIn the small to medium power range the main technologies for the conversion of biomass sources into electricity are based either on internal combustion engines or Organic Rankine cycles. Relatively low electric efficiencies are obtained in both cases due to thermodynamic losses in the conversion of biomass into syngas and to the heat transfer between combustion gases and working fluid, respectively. Higher efficiencies can be obtained using the supercritical closed CO2 Brayton cycles, the applications of which are restricted in the literature to nuclear power plants and more recently to concentrating solar power plants. The cascaded configuration of two supercritical CO2 cycles enables to overcome the intrinsic limitation of the single cycle in the effective utilization of the whole heat available from the heat source. The aim of this paper is to evaluate whether this power plant configuration could be a good alternative option in the conversion of biomass sources into electricity, which was never explored in the literature up to now. The focus is on the search of the thermodynamic operating parameters which maximize power output. Results of the optimization procedure show that a total heat recovery efficiency in the range 30-34% can be achieved, which is approximately 5%-points higher than that of the existing biomass power plants in the small to medium power range
Evolutionary Algorithms for Multi-Objective Energetic and Economic Optimization in Thermal System Design
No full textThermoeconomic analyses in thermal system design are always focused on the economic objective.
However, knowledge of only the economic minimum may not be sufficient in the decision making process,
since solutions with a higher thermodynamic efficiency, in spite of small increases in total costs, may result
in much more interesting designs due to changes in energy market prices or in energy policies. This paper
suggests how to perform a multi-objective optimization in order to find solutions that simultaneously satisfy
exergetic and economic objectives. This corresponds to a search for the set of Pareto optimal solutions
with respect to the two competing objectives. The optimization process is carried out by an evolutionary
algorithm, that features a new diversity preserving mechanism using as a test case the well-known CGAM
problem. 2002 Elsevier Science Ltd. All rights reserved
A method to separate the problem of heat transfer interactions in the synthesis of thermal systems
No full textMost of the efforts to improve energy system configurations are directed towards the recovery of internal heat, which reduces the contribution of the external hot source and enhance system efficiency accordingly. This problem is strictly related to the synthesis of different components into system topology, i.e. with the definition of the optimal system configuration according to specified objectives.
A new method for the optimization of the heat transfer interactions within energy systems is presented here, based on the idea of cutting thermal links between the “basic” components of the system. The boundary temperatures of hot and cold flows that are generated as a consequence of these cuts are evaluated in an optimization procedure that involves the design parameters of the system as well. The high potential of the proposed method consists in separating the problem of defining the system configuration into two separate sub-problems, the first regarding the definition of the “basic” topology of the system (related to all components different from the heat exchangers), the second the optimal heat transfer interactions within the system. This feature makes complex systems today only marginally “optimizable”, amenable to complete optimization. The method is applied to a humid air turbine (HAT) cycle plant, which represents a good test to prove its reliability and generality, due to the internal recirculation of mass and energy flows
A New Thermoeconomic Method for the Location of Causes of Malfunctions in Energy Systems
No full textDiagnosis procedures primarily aim at locating the control volumes where anomalies occurred. This is not a simple task, since the effects of anomalies generally propagate through the whole system and affect the behavior of several components. Some components may therefore present a reduced efficiency, although they are not sources of operation anomalies, due to non flat efficiency curves. These induced effects are a big obstacle in the use of thermoeconomic techniques for the search of the origin of the anomalies. On the other hand, the real cause of the alteration of component behavior is the modification of its characteristic curve, due to degradation or failures. According to this concept, a new approach, based on an indicator measuring the alteration of the characteristic curve of the component affected by the operation anomaly, is proposed and applied to a test case power plant.</p
Prediction of performance and emissions of a two-shaft gas turbine from experimental data
No full textPrecise performance evaluation at design and off-design operations is needed for a correct management of power plants. This need is
particularly strong in gas turbine power plants, which can quickly react to load variations and are very sensitive to ambient conditions.
The paper aims at presenting a simple tool to determine the values of the thermodynamic quantities in each point of the plant and the
overall plant performances of a real gas turbine plant. Starting from experimental data, a zero-dimensional model is developed, which
properly considers the effect of ambient conditions and water injection for pollutant abatement at different load settings under the action
of the control system. In particular, semi-empirical correlations for pollutant emissions taken from the literature are adapted by tuning
their coefficients on the experimental data, in order to predict carbon monoxide and nitrogen oxide pollution. Such a tool can be useful to
manage the energetic, economic and environmental aspects of plant operation
Realizzazione di una nuova serie di giranti per ventilatori industriali a flusso assiale
No full textRapporto per F.lli Ferrari Ventilatori Industriali S.p.A
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