Study on the use of ejectors for capacity modulation and performance improvement in CO2 commercial refrigeration systems.

Expansion work recovery by means of a two-phase ejector is an attractive option for improving the efficiency of CO2 commercial refrigeration systems. However, the use of ejectors in a system subject to varying ambient conditions and capacity requirements presents a significant challenge, as ejectors have been seen to offer poor performance at off-design conditions. In order for ejector systems to be a realistic option for efficiency improvement, they must be able to operate efficiently at off-design and reduced capacity conditions. In this paper, existing CO2 ejector data from the open literature is analyzed in order to see the impact on ejector component and system performance for operating an ejector cycle at off-design conditions, and different methods for addressing the issue of off-design and reduced capacity operation of ejector cycles are discussed. A theoretical model is used to investigate the performance of different CO2 commercial refrigeration cycle configurations with two-phase ejectors.