Development of an improved transcritical refrigeration system using natural refrigerants for low-temperature applications

Low-temperature refrigeration has an essential role in food, pharmaceutical, and chemical industries. Being deep-freezing applications, typically below -30 °C, the system performance in terms of the coefficient of performance is in the range of 1.0 to 1.1. In this work, we demonstrate the development of a hybrid system by implementing a transcritical refrigeration cycle with an ejector and an organic Rankine cycle for performance improvement. Considering ecological concerns, natural refrigerants, i.e., carbon dioxide (R744) and propylene (R1270) were employed as the working fluids. A mathematical model was developed for the transcritical refrigeration cycle, the ejector and the organic Rankine cycle based on the conservation of energy and mass. The pressure levels of the ejector inlet and outlet for optimum performance were evaluated. It is observed that the current hybrid cycle delivers the coefficient of performance up to 1.5, which is 25 – 50% improvement as compared to a conventional transcritical cycle.