Abstract
An ejector-expansion refrigeration cycle using nitrous oxide was assessed. Thermodynamic analyses, including energy and exergy analyses, were carried out to investigate the effects on performance of several key factors in the system. The results show that the ejector-expansion refrigeration cycle (EERC) has a higher maximum coefficient of performance and exergy efficiency than the internal heat exchanger cycle (IHEC), by 12% and 15%, respectively. The maximum coefficient of performance and exergy efficiency are 14% and 16.5% higher than the corresponding values for the vapor-compression refrigeration cycle (VCRC), respectively. The total exergy destruction for the N2O ejector-expansion cycle is 63% and 53% less than for IHEC and VCRC, respectively. Furthermore, the highest COPs for the vapor-compression refrigeration, the internal heat exchanger and the ejector-expansion refrigeration cycles correspond to a high side pressure of 7.3 MPa, and the highest COPs for the three types of CO2 refrigeration cycles correspond to a high side pressure of 8.5 MPa. Consequently, these lead to a lower electrical power consumption by the compressor.
Highlights
Various refrigerants are used presently in vapor compression refrigeration cycles
The comparison between three types of N2O refrigeration cycles shows that the maximum coefficient of performance for the cycles occurs at roughly the same high side pressure, and that the maximum value is exhibited by the expansion refrigeration cycle (EERC) cycle
The highest coefficient of performance (COP) in this study corresponds to a high side pressure of 7.3 MPa for three types of N2O refrigeration cycles, but about 8.5 MPa for three types of CO2 refrigeration cycles
Summary
Various refrigerants are used presently in vapor compression refrigeration cycles. concerns have been repeatedly raised about many refrigerants, due to their environmental characteristics such as ozone depletion potential, global warming potential and atmospheric lifetime (ALT). Sarkar and Bhattacharyya [7] thermodynamically optimized the compressor discharge pressure in a conservative trans-critical N2O refrigeration cycle, and investigated the effect of superheating in the evaporator, internal heat exchange and the use of a recovery turbine instead of an expansion valve on cycle behavior. Choudhary et al [24] analyzed a novel N2O based trans-critical refrigeration system in which an ejector is used as an expansion device Their system is found to have a higher COP, a lower compressor discharge pressure and a higher entrainment ratio but suffers from having a lower volumetric cooling capacity. This investigation aims to improve understanding of the system, and help in comparing its performance with the performances of other refrigeration system
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