1,721,033 research outputs found
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
Systematic Two-Dimensional Cascade Optimization using Genetic Algorithms: Preliminary Results
No full textOn the thermoeconomic approach to the diagnosis of energy system malfunctions. Part-5 Indicators to Diagnose Malfunctions: Application of a New Indicator for the Location of Causes
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 the thermoeconomic indicators for the search of the origin of the anomalies. As discussed in a brief overview of the several thermoeconomic indicators suggested in the literature, the reason for this inability is the focus on specific exergy consumptions as independent variables of the thermoeconomic model of the energy system. Instead, the real cause of the alteration of component behavior is the modification of its characteristic curve. Based on this concept, a new indicator measuring the alteration of the characteristic curve of the component affected by the operation anomaly is discussed and applied to the combined cycle power plant of the TADEUS problem
Energy System Diagnosis by an Expert System with a Genetically Evolved Database of Fuzzy Rules
No full textThe problem of malfunction diagnosis in energy systems can be approached using an
expert system which compares the experimental data measured by the plant acquisition
system and the calculated data evaluated by a plant simulator under the same operating
conditions. In this paper the rules that form the "knowledge base" of the expert system are
not assigned heuristically by trying to code the expertise of plant personnel, as it is usually
done, but they are artificially and randomly generated by the recombination and selection
operators of an evolutionary algorithm. A two-objective optimization problem is set up, in
order to search for the optimal sets of rules having the minimum complexity but
simultaneously maximizing the number of correct fault identifications for a given set of
malfunctioning operating conditions. A global and a local approach are applied to a real
test case, a two-shaft gas turbine used as the gas section of a combined-cycle cogeneration
plant, in order to evaluate the potentialities and the limits of this methodology
Building the basic configuration of compression refrigeration systems with the SYNTHSEP method
No full textThe SYNTHSEP method has been proposed as a bottom-up approach to build the basic configuration of energy conversion systems starting from elementary thermodynamic cycles. These elementary cycles, which are considered as the unit bricks forming the basic configuration of any energy conversion system, simply consist of the four fundamental thermodynamic processes (a compression, an expansion, a heating and a cooling). Processes of the same type can be shared between/among different cycles in the basic configuration of the system, according to its topology. In previous works by the same Authors, the SYNTHSEP method has been applied to the optimal synthesis and design of power generation systems (ORCs, steam cycles), the basic configuration of which was made of direct cycles (compression, heating, expansion, cooling). In this work it is shown conceptually how the SYNTHSEP method can be applied to compression refrigeration system as well, using reverse cycles (compression, cooling, expansion, heating) as the unit bricks for the synthesis of the basic configuration of the system. In particular, the focus is on the rules to reconcile the information on the topology of the basic configuration, indicating the processes that are shared between/among the cycles, with the information about the design parameters of the cycles
A practical tool to generate complex energy system configurations based on the SYNTHSEP methodology
Full text linkTraditional fossil fuelled power plants are commonly based on steam Rankine cycle or Brayton Joule cycle. Using water or air as working fluid is obviously the most obvious choice for the wide availability of these substances in nature. However, the scarcity of natural energy sources and the strong need of reducing environmental impact have necessarily drawn the research to new energy systems configurations operating with other working fluids, which are able to recover lower temperature sources, such as Sun or industrial wasted heat. The variety of new working fluids (refrigerants or organic fluids) widens the choice to a variety of configurations that can be tailored to the specific source characteristics and boundary constraints. It is not always easy or even possible to conceive the best configuration for given specifications with the mere experience of a common designer. To design a new system configuration, the designer normally uses some “non-codified rules” deriving from his knowledge of basic thermodynamics and energy engineering. This paper aims instead at showing a practical tool that is based on a new methodology, named SYNTHSEP, to generate new energy system configurations. This methodology starts from the simple thermodynamic cycles operated by a given fluid made up of the four fundamental processes (compression, heating, expansion and cooling) and uses a rigorous set of codified rules to build the final system configuration. The paper presents the basics of the new methodology and how it has been implemented in a practical tool that simply requires the information about the elementary cycles and their shared processes as input data
The HEATSEP method for the synthesis of thermal systems: An application to the S-Graz cycle
No full textIn the last decades component synthesis has become a critical issue in the research field about new highly integrated energy conversion systems. Several heuristic methodologies following experience-based guidelines have been proposed to simplify the problem of synthesis optimization. This paper describes an application of the HEATSEP method, which consists in the isolation of all the heat transfer processes of an energy system in an undefined “black-box”. Then, synthesis optimization can be split in two subproblems, the first about the synthesis/design optimization of the basic plant configuration (which is made up of all the components but heat transfer devices) and the other about the synthesis of the heat exchanger network inside the black-box. The chosen test case is the design optimization of the basic plant configuration of an S-Graz cycle based power plant, as it is suitable to show the potentialities of the method
An Experimental Investigation of the Flow Field Pattern within the Impeller of a Cross-Flow Fan
No full textCross-flow fan performance is strongly influenced by the geometry of the casing, as the latter, in turn, affects the position and the strength of the eccentric vortex that characterizes the operation of this category of fans. The paper presents a systematic experimental investigation of the flow field within the impeller at different throttling conditions and for different geometries of the fan casing. Both pressures and velocities are measured using a three-dimensional five-hole probe that is inserted in the flow. This study helps determine the relationship between the design parameters of the casing and the flow field pattern, and it is part of an extensive work, by the same research group, aimed at establishing a general theory on cross-flow fan operation and at outlining the design guidelines for this particular type of turbomachine
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