Abstract
Comparative energy and exergy investigations are reported for a transcritical N2O refrigeration cycle with a throttling valve or with an expander when the gas cooler exit temperature varies from 30 to 55 °C and the evaporating temperature varies from −40 to 10 °C. The system performance is also compared with that of similar cycles using CO2. Results show that the N2O expander cycle exhibits a larger maximum cooling coefficient of performance (COP) and lower optimum discharge pressure than that of the CO2 expander cycle and N2O throttling valve cycle. It is found that in the N2O throttling valve cycle, the irreversibility of the throttling valve is maximum and the exergy losses of the gas cooler and compressor are ordered second and third, respectively. In the N2O expander cycle, the largest exergy loss occurs in the gas cooler, followed by the compressor and the expander. Compared with the CO2 expander cycle and N2O throttling valve cycle, the N2O expander cycle has the smallest component-specific exergy loss and the highest exergy efficiency at the same operating conditions and at the optimum discharge pressure. It is also proven that the maximum COP and the maximum exergy efficiency cannot be obtained at the same time for the investigated cycles.
Highlights
Chlorofluorocarbon (CFC) and hydrofluorocarbon (HFC) refrigerants are known to be sources of environmental damage: global warming, ozone depletion, greenhouse gas emissions, and air pollution
In the transcritical CO2 cycle, the coefficient of performance (COP) is significantly influenced by the discharge pressure [20,23]
An optimum discharge pressure exists that leads to the maximum COP for a given gas cooler exit
Summary
Chlorofluorocarbon (CFC) and hydrofluorocarbon (HFC) refrigerants are known to be sources of environmental damage: global warming, ozone depletion, greenhouse gas emissions, and air pollution. The Montreal protocol countries [1] have agreed to gradually replace CFCs and HFCs with new refrigerants Owing to their zero ozone depletion potential (ODP) and low global warming potential (GWP), several natural refrigerants such as carbon dioxide, nitrous oxide, air, water, ammonia, and propane have received increasing attention as future refrigerants [2]. The applications and performance analysis of Compared investigations of CO2have cycles, research on refrigeration systems using N2O as the transcritical. A comparative energy and exergy analysis is performed on a transcritical N2O and compared it with a similar cycle configuration of CO refrigeration cycle with a throttlingenergy valve and with ananalysis expander. The results are compared with CO2 cycles that have the same configuration
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