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A gas ejector for CO2 supercritical cycles

Palacz, Michal, Haida, Michal, Smolka, Jacek, Plis, Marcin, Nowak, Andrzej J., Banasiak, Krzysztof
Energy 2018 v.163 pp. 1207-1216
carbon dioxide, energy, refrigeration
The CO2 ejectors are recently often used as the main expansion device in the modern refrigeration cycles. On the other hand, according to the newest literature the implementation the ejectors into supercritical CO2 power cycles increase its performance. The recent studies showed that in case of the power cycles the ejector pressure lift and mass entrainment ratio are relatively high. Therefore, the main scope of this paper is the investigation of the possibilities of designing the ejector for supercritical Brayton CO2 system. The CFD based computational tool was used to design the ejector for the considered cycle. The system analysis was used to define the ejector on design point. The results of that analysis showed that the required pressure lift and must be equal to 103 bar and mass entrainment ratio equal to 0.995, respectively. The CFD-based evaluation of the proposed ejector showed that these values are impossible to achieve. Therefore, the modifications of the crucial ejector dimensions was performed to increase its performance. Nevertheless, the maximum possible pressure lift for the proposed ejector was equal to 60 bar The analysis of the gathered results showed that the design of the ejector fulfilling the system requirements may be impossible to achieve.