Avaliação experimental do emprego de ejetores em um ciclo de refrigeração transcritico de CO2

Abstract

This work presents an experimental analysis of the energy and environmental performance of a transcritical CO₂ refrigeration cycle, focusing on the thermodynamic effects of the ejector on system efficiency. First, comparative tests were conducted on the baseline refrigeration cycle, varying the evaporation temperature between –12 °C and –3 °C and the gas-cooler outlet temperature between 31 °C and 37 °C. The high-pressure valve opening was adjusted between 60 % and 90 %, allowing evaluation of how the gas-cooler pressure influences the system’s energy efficiency and the establishment of reference results. Next, the ejector was installed between the liquid line and the evaporator outlet, enabling the achievement of lower evaporation temperatures—down to –15 °C—and gas-cooler outlet temperatures up to 40 °C for the thermal load. These conditions were not attainable in the baseline cycle due to the high compressor discharge temperature, experimentally demonstrating the ejector’s potential to reach lower evaporation temperatures. In the third stage, the average results were compared. An average reduction in discharge temperature of up to 24.5 °C was observed, accompanied by an average increase in cooling capacity of up to 63 % and an average decrease in power consumption of 26.2 %. These combined effects resulted in an average increase in COP of up to 121 %. This behavior can be explained by the increased specific cooling capacity due to the presence of the phase separator, coupled with the increased mass flow rate as the gas-cooler outlet temperature rises, resulting in less COP degradation compared to the conventional transcritical cycle. Regarding environmental impacts, scenarios in Brazil, Saudi Arabia, France, and the United States were analyzed. These scenarios present different conditions for recovery factors and indirect emissions, in order to assess the varied environmental impacts across different locations. In general, the importance of energy-efficient refrigeration systems in significantly reducing emissions is highlighted. Among the evaluated scenarios, the greatest environmental impact was observed in Saudi Arabia, due to its high indirect emissions coefficient.