Exergy–based ecological optimization for an endoreversible variable–temperature heat reservoir air heat pump cycle
Yuehong Bi a,b, Lingen Chenb,*, and Fengrui Sunb
ª Institute of Civil & Architectural Engineering, Beijing University of Technology, Beijing 100124, P.R. China,
b Postgraduate School, Naval University of Engineering, Wuhan 430033, P.R. China, Tel: 0086–27–83615046; Fax: 0086–27–83638709 e–mail: lgchenna@yahoo.com *; lingenchen@hotmail.com *
Recibido el 1 de diciembre de 2008 ]]> Aceptado el 20 de enero de 2009
Abstract
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.
Keywords: Exergy–based ecological function; endoreversible air heat pump; variable–temperature heat reservoir; finite time thermodynamics.
Resumen
Un análisis y una optimización ecológicos de funcionamiento basados en el análisis exergetic se realiza en este papel para un ciclo endoreversible de la pompa de calor del aire con los depósitos del calor de la variable–temperatura. Un criterio ecológico exergy–basado de la optimización, que consiste en el maximizar de una función que representa el mejor compromiso entre el índice de salida del exergy y el índice de la perdida del exergy (producto de la temperatura de la tarifa y del ambiénte de la generación de la entropía) del ciclo de la pompa de calor, se toma como la función objetiva. La relación analítica de la función ecológica exergy–basada se deriva. Los efectos del cociente de la presión, de la eficacia de los cambiadores de calor, del cociente de la temperatura de la entrada de los depósitos del calor y del cociente de la temperatura de la entrada del depósito del calor del caliente–lado a la temperatura ambiénte en la función ecológica se analizan. Las optimizaciones del funcionamiento del ciclo son realizadas buscando la distribución óptima de la conductancia del calor de los cambiadores calientes y del frío–lado de calor para el inventario total fijo del cambiador de calor y la tarifa óptima de la capacidad de calor que empareja entre el líquido de funcionamiento y los depósitos del calor, respectivamente. Las influencias de algunos parámetros de diseño, incluyendo inventario del cambiador de calor y el índice de capacidad de calor del líquido de funcionamiento en el funcionamiento óptimo de la pompa de calor endoreversible del aire son proporcionadas por ejemplos numéricos. Los resultados demuestran que la optimización ecológica exergy–basada es un criterio importante y eficaz para la evaluación de las pompas de calor del aire.
Descriptores: Función ecológica exergy–basada; pompa de calor endoreversible del aire; depósito del calor de la variable–temperatura; termodinámica de tiempo finitas.
]]> PACS: 01.40G; 05.70.–a; 64.70.F
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Acknowledgements
This paper is supported by Scientific Research Common Program of Beijing Municipal Commission of Education (Project No: KM200710005034) and Program for New Century Excellent Talents in University of P. R. China (Project No: NCET–04–1006).
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