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Many applications and industrial processes require very low cooling temperature, such as cold storage in the biomedicalfield, requiring temperature below -80 °C. However, single-cycle refrigeration systems can only achieve the effectivecooling temperature of -40 °C and, also, the performance of the cycle will decrease drastically for cooling temperatureslower than -35°C. Currently, most of cascade refrigeration systems use refrigerants that have ozone depletion potential(ODP) and global warming potential (GWP), therefore, in this study, a cascade system is simulated using a mixture ofenvironmentally friendly refrigerants, namely, carbon dioxide and a hydrocarbon (propane, ethane or ethylene) as therefrigerant of the low temperature circuit. A thermodynamic analysis is performed to determine the optimal compositionof the mixture of carbon dioxide and hydrocarbons in the scope of certain operating parameters. In addition, aneconomic analysis was also performed to determine the annual cost to be incurred from the cascade refrigeration system.The multi-objective/thermoeconomic optimization points out optimal operating parameter values of the system, toaddressing both exergy efficiency and its relation to the costs to be incurred. |
