EXPERIMENTAL COMPARISON OF THE PERFORMANCE OF A CO2 EJECTOR CYCLE FOR TRANSCRITICAL AND SUBCRITICAL OPERATION

The use of a two-phase ejector to improve the COP and capacity of CO2 vapor compression systems has been a topic of much research in recent years. Studies often investigate the performance of the CO2 ejector cycle when operated in transcritical mode, focusing on controlling and optimizing high-side pressure. However, less focus is given to subcritical operation of CO2 ejector cycles as well as how well the same ejector and system can operate in both modes. This paper presents the results of an experimental investigation of a CO2 ejector cycle over a range of ambient temperatures, allowing the system to operate in both transcritical and subcritical modes. An adjustable ejector using a needle to control nozzle throat size, often used in CO2 ejector studies, is used to control high-side pressure and improve COP for transcritical mode. It is observed that the adjustable ejector can be used to control and optimize the performance of the system for subcritical operation as well with a similar control concept as used for transcritical operation.