EXERGETIC ANALYSIS OF A R717/R744 CASCADE REFRIGERATION SYSTEM

João Gabriel de Oliveira Marques¹; Paulo Eduardo Lopes Barbieri¹

¹ Centro Federal de Educação Tecnológica de Minas Gerais

doi:10.20906/CPS/COB-2015-0420

Resumo

There is a growing search for the development of technologies that operate with the highest efficiency level. At the same time, it is desirable that these technologies have the lowest operational cost. Inside this context are the cascade refrigeration systems that use refrigerants R-717 and R-744. Their ideal operational condition is the maximum efficiency combined with the minimum cost. However, in general, increasing the efficiency implies increasing the cost. Thus, the objective of this study is to investigate the relationship between the maximum exergy efficiency and the minimal operating cost for a R717/R744 cascade refrigeration system. The methodology consists on the development of a exergetic model to describe the behavior of the system. The model includes equations about the operational cost and the exergetic efficiency, both used in the simulations to maximize the exergy efficiency and minimize operating cost. The results show that, for the system, the maximization of exergy efficiency provides the minimum operational cost. Analogously, the minimization of cost results in maximum efficiency. Based on the results, it is conclusive that, for the operation of a R717/R744 cascade refrigeration systems, the maximum exergetic efficiency and minimum operational cost occur simultaneously.

Palavras-chave: Refrigeration; Simulation; Thermodynamics; Exergetic Analysis; Operational Cost