Performances des systèmes frigorifiques trans-critiques utilisant le CO2 comme fluide frigorigène

Abstract

The negative impact of synthetic fluids on the environment has led researchers to natural refrigerants, although these fluids are not harmful on the environment, some of them are dangerous because of their flammability and toxicity. Therefore, carbon dioxide goes into very good position among the other natural fluids. The thermodynamic properties of CO2 require a trans-critical cycle. Unfortunately, this cycle has low performance compared to conventional cycles. The main objective of this work is to improve the performance of the refrigeration systems using CO2 as refrigerant and study the heat transfer of carbon dioxide in evaporation. Based on the first law of thermodynamics and the optimization analysis several trans-critical cycles were studied, in addition, new proposed cycles have been proposed and studied. As regards the study of heat transfer during evaporation of CO2, literature review has shown that there are several correlations used to predict the coefficient of heat transfer. In order to evaluate these correlations and select the best correlation allowing the optimal design of evaporator, which ensures the required cooling capacity, an experimental database was extracted from different papers available in the literature and compared with these correlations.