Multistage Irreversible Coupling The Refrigeration Cycle Performance Optimization

Finite-time thermodynamics is the extension and generalization of classical thermodynamics. It is a new branch of the modem therrnodynaniics. To find the minimum irreversible loss under a finite time constraint is a main task in finite time thermodynamics, and thus the concepts of entropy and exergy are always involved. In this paper, the theory of finite-time thermodynamics and the method of exergy analysis are used to investigate the optimum performance of a multi-stage irreversible combined refrigeration system. Firstly, a general cycle model of a multi-stage inevemible combined refrigeration system is established. The influence of thermal resistance, heat leak and internal irreversibility of the working fluid on the performance of the cycle system is studied. The fundamental optimum relation between the coefficient of performance and the dimensionless cooling rate is derived. Secondly, based on the fundamental optimum relation, exergy concept, and exergy analysis method, the optimal performances related to the exergy of the refrigerator, such as the rate of exergy output, the efficiency of exergy output, and the rate of exergy loss, are discussed. The characteristic curves relative to these parameters are presented and expounded. A novel and useful performance bound is obtained. Finally, the ecological function E is taken as an objective function for IThther optimization. Some significant discussions are done. The results show that the state of the maximum ecological function is worth~ile to consider in the research and manufacture of real thennodynamicAbstractcycles.The results obtained here are quite general. They may be used to discuss the optimal performance of an arbitrary-stage reversible, endoreversible, andirreversible combined refrigeration system as long as one chooses suitably the values of the main parameters m the cycle model. And consequently, they pn~de some new theoretical bases for the optimal design and the selection of optimal operating condition of real refrigeration systems.