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Throttling process through expansion valves causes a considerable amount of exergy loss so that reducing this loss improves the performance of compressed refrigeration cycle considerably. In the present work, the effect of using an ejector on the performance of a cascade refrigeration cycle is evaluated. It is concluded that the using ejector and selecting R134a as the high temperature circuit refrigerant cause the COP and second law efficiency to increase by approximately 6.5 percent as compared to the conventional cascade cycle with the same cooling capacity. In addition, several refrigerants including R717, R290, R134a, and R123 are examined to reveal the effect of refrigerant type in the high temperature circuit on the cycle performance. It is also found that, at a temperature of more than 255.4 K, for the evaporator of high temperature circuit, the refrigerant combination of R744-R123 results in a better performance as compared to the other combinations. Finally, the cycle performance is optimized with respect to the temperatures of low temperature evaporator, high temperature evaporator, and the ambient from the view points of both the first and second laws of thermodynamics. It is concluded that the COP and the second law efficiency are the highest when R123 is used as the refrigerant at the high temperature circuit.

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An ejector-expansion refrigeration cycle employing N2O is studied in this paper and thermodynamic and exergy analysis is carried out to find out the effect of some key factor within the system. The results show that Ejector-Expansion Refrigeration Cycle (EERC) obviously has the highest maximum coefficient of performance and exergy efficiency by about 12% and 14% more than Internal Heat Exchanger Cycle (IHEC); meanwhile these are about 15% and 16.5% higher than Vapor-Compression Refrigeration Cycle (VCRC) ones, respectively. Moreover, the total exergy destruction in N2O ejector-expansion cycle is 63.3% and 54% less than IHEC and VCRC and the exergy destructed in expansion process within EERC is 19.39% and 40.497% of total destruction less than IHEC and VCRC. Furthermore, the highest COP for vapor-compression refrigeration, internal heat exchanger and ejector-expansion refrigeration cycles is corresponding to the high side pressure of 7.328 Mpa, while this value for CO2 refrigeration cycle is about 8.5 Mpa.