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Equivalence between the application of entransy and entropy generation

Oliveira, Santiago del Rio; Milanez, Luiz Fernando
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 518-525
ENG
Relevância na Pesquisa
36.19%
Recently, a group of researchers proposed the concept of entransy by analogy with the electrical energy stored in a capacitor, the entransy being a measure of the ability of a body or a system to transfer heat. In comparative terms, the entransy dissipation rate is related with the loss of heat transfer ability just like the exergy destruction rate is proportional to the loss of work ability, being these losses caused by the irreversibilities related to the thermodynamic processes. Some authors have questioned the need for the concept of entransy, claiming that this concept is only an extension of a well established theory of heat transfer. The objective of this work is show the equivalence between the application of the concepts of entransy and entropy generation rate, which can be verified using various application examples. The application examples used here are the thermodynamic modeling of three physical models of solar energy collectors and a physical model of a sensible heat storage system. Analytical results are shown and compared. The results showed that the application of the concept of entransy provided identical expressions obtained by the concept of entropy generation, indicating a duplication of concepts. (C) 2014 Elsevier Ltd. All rights reserved.

Exergy efficiency optimization for gas turbine based cogeneration systems

Ferreira, Ana C. M.; Teixeira, S. F. C. F.; Teixeira, J. Carlos; Nunes, Manuel L.; Martins, Luís Barreiros
Fonte: ASME Publicador: ASME
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
Relevância na Pesquisa
36.31%
Energy degradation can be calculated by the quantification of entropy and loss of work and is a common approach in power plant performance analysis. Information about the location, amount and sourc es of system deficiencies are determined by the exergy analysis, which quantifies the exergy destruction. Micro - gas turbines are prime movers that are ideally suited for cogeneration applications due to their flexibility in providing stable and reliable power. This paper presents an exergy analysis by means of a numerical simulation of a regenerative micro - gas turbine for cogeneration applications . The main objective is to study the best configuration of each system component , considering the minimization of the system irreversibilities . Each component of the system was evaluated considering the quantitative exergy balance . Subsequently the optimization procedure was applied to the mathematical model that describes the full system. The rate of irreversibility, efficiency and flaws are highlighted for each system component and for the whole system. The effect of turbine inlet temperature change on plant exergy destruction was also evaluated . The results disclose that considerable exergy destruction occurs in the combustion chamber. Also...

Metodologia para an?lise exerg?tica-econ?mica de plantas a vapor para gera??o de eletricidade consumido res?duo de biomassa amaz?nica

MENDES, Manoel do Esp?rito Santo dos Santos
Fonte: Universidade Federal do Pará Publicador: Universidade Federal do Pará
Tipo: Dissertação de Mestrado
POR
Relevância na Pesquisa
16.15%
A disponibilidade de recursos energ?ticos em um pa?s impacta diretamente no seu desenvolvimento s?cio-econ?mico. Com a eleva??o dos pre?os dos energ?ticos no Brasil, a eficientiza??o do uso de energia tornar-se uma atividade estrat?gica para o setor industrial. Com esse intuito as avalia??es energ?ticas empregadas nesse setor objetivam otimizar a efici?ncia dos seus sistemas t?rmicos. Essas avalia??es de desempenho energ?tico s?o baseadas na Primeira Lei da Termodin?mica e s?o capazes de identificar apenas as perdas de energia, diferente da avalia??o exerg?tica que permite qualificar essa energia perdida. Devido a essa an?lise de qualifica??o da energia ser sofisticada e demorada, tornar-se necess?rio desenvolver um protocolo que seja executado de forma r?pida e que contemple as particularidades da Amaz?nia, tanto o clima quanto a sua biomassa. Para isto, este trabalho prop?e e aplica uma metodologia atrav?s do emprego de an?lises energ?ticas, exerg?tica e exergo-econ?mica em uma planta de pot?ncia a vapor instalada no Estado Par? e operando com ciclo Rankine. Com aplica??o dessas avalia??es obt?m-se as taxas de energia e de perdas de energia, as taxas de exergia, as taxas de destrui??o de exergia, as taxas de custo de cada produto e o custo monet?rio da capacidade energ?tica produzida pela planta em R$/kWh. Com esses resultados foi poss?vel identificar as maiores perdas energ?ticas da planta...

Heating load, COP, exergy loss rate, exergy output rate and ecological optimizations for a class of generalized irreversible universal heat pump cycles

Chen,Lingen; Feng,Huijun; Sun,Fengrui
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2010 EN
Relevância na Pesquisa
96.53%
The optimal performance of a class of generalized irreversible universal steady flow heat pump cycle model, which consists of two heat-absorbing branches, two heat-releasing branches and two irreversible adiabatic branches with the losses of heat-resistance, heat leakage and internal irreversibility is analyzed by using finite time thermodynamics. The analytical formulae about heating load, coefficient of performance (COP), exergy loss rate, exergy output rate and ecological function of the universal heat pump cycle are derived. Moreover, performance comparisons among maximum COP condition, a given exergy output rate condition and maximum ecological function condition are carried out by using numerical examples. It is shown that the ecological function objective is an excellent candidate objective with the ideal of an ecological and long-term goal. The effects of heat leakage and internal irreversibility on the cycle performance are discussed. The universal cycle model gives a unified description of seven heat pump cycles, and the results obtained include the performance characteristics of Brayton, Otto, Diesel, Atkinson, Dual, Miller and Carnot heat pump cycles with the losses of heat-resistance, heat leakage and internal irreversibility.

Exergy-based ecological optimization for an endoreversible variable-temperature heat reservoir air heat pump cycle

Bi,Yuehong; Chen,Lingen; Sun,Fengrui
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2009 EN
Relevância na Pesquisa
56.4%
An ecological performance analysis and optimization based on the exergetic analysis is carried out in this paper for an endoreversible air heat pump cycle with variable-temperature heat reservoirs. An exergy-based ecological optimization criterion, which consists of maximizing a function representing the best compromise between the exergy output rate and exergy loss rate (entropy generation rate and environment temperature product) of the heat pump cycle, is taken as the objective function. The analytical relation of the exergy-based ecological function is derived. The effects of pressure ratio, the effectiveness of the heat exchangers, the inlet temperature ratio of the heat reservoirs and the ratio of hot-side heat reservoir inlet temperature to ambiént temperature on ecological function are analyzed. The cycle performance optimizations are performed by searching the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for fixed total heat exchanger inventory and the optimum heat capacity rate matching between the working fluid and the heat reservoirs, respectively. The influences of some design parameters, including heat exchanger inventory and heat capacity rate of the working fluid on the optimal performance of the endoreversible air heat pump are provided by numerical examples. The results show that the exergy-based ecological optimization is an important and effective criterion for the evaluation of air heat pumps.