A performance comparison of fixed ejectors with and without a swirl generator and controllable ejectors in a CO2 refrigeration system

This paper provides a performance comparison ejector technology to be installed in a CO₂ supermarket refrigeration system. Namely, the fixed ejectors with and without swirl flow at the inlet of the motive and suction nozzles and the fixed and controllable ejectors equipped with convergent and convergent-divergent nozzles and were analysed. The Coefficient of Performance (COP) of the ejector-based refrigeration system is dependent on the design and control of the mass flow rate through this device. The literature suggests that one of the possible ejector efficiency improvements can be performed using a swirl generator at the inlet of the motive nozzle. Therefore, a swirl generator was simulated for different size CO₂ ejectors under typical operating conditions in a supermarket and for a range of rotational speeds. In addition, the performance of a group of fixed ejectors working in parallel was compared with two controllable ejectors with a needle. To analyse the potential of the considered approaches, the device performance was numerically simulated using the validated Homogeneous Equilibrium Model (HEM) model for the same typical transcritical parameters. For all the fixed ejectors with and without the swirl generator, devices of various sizes were simulated and compared with the corresponding controllable ejector performance at a few needle positions. For both ejector types, a global efficiency as a function of the mass flow rate was presented and discussed.