Résumé:
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.
