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.