Comparison of transcritical CO2 refrigeration cycle with expander and throttling valve including/excluding internal heat exchanger: Exergy and energy points of view

The article compares four compression evaporative refrigeration cycles from energy and exergy points of view where carbon dioxide is considered as the working fluid. The four cycles are: (1) the cycle with expander, (2) the cycle with expander and internal heat exchanger, (3) the cycle with throttling and (4) the cycle with throttling and internal heat exchanger. In the cycles, effect of evaporation temperature and exhaust temperature of gas cooler on Coefficient of Performance (COP) and exergy efficiency are taken into consideration. From the energy and exergy points of view, the results indicate that using heat exchanger reduces COP and exergy efficiency of the cycle with expander while the use of heat exchanger in the cycle with throttling valve enhances the COP and exergy efficiency. The comparison between the four cycles reveals that the cycle with expander and without internal heat exchanger has the highest COP and exergy efficiency.