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Article

A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles

1
Department of Mechanics, Tianjin University, Tianjin 300350, China
2
Department of Mechanics and Maritime Sciences, Chalmers University of Technology, 41296 Gothenburg, Sweden
*
Author to whom correspondence should be addressed.
Energies 2020, 13(19), 5049; https://doi.org/10.3390/en13195049
Received: 17 August 2020 / Revised: 21 September 2020 / Accepted: 22 September 2020 / Published: 25 September 2020
Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency. View Full-Text
Keywords: supercritical carbon dioxide; centrifugal compressor; impeller inlet design; maximum swallowing capacity; condensation supercritical carbon dioxide; centrifugal compressor; impeller inlet design; maximum swallowing capacity; condensation
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MDPI and ACS Style

Li, X.; Zhao, Y.; Yao, H.; Zhao, M.; Liu, Z. A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles. Energies 2020, 13, 5049. https://doi.org/10.3390/en13195049

AMA Style

Li X, Zhao Y, Yao H, Zhao M, Liu Z. A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles. Energies. 2020; 13(19):5049. https://doi.org/10.3390/en13195049

Chicago/Turabian Style

Li, Xiaojian, Yijia Zhao, Huadong Yao, Ming Zhao, and Zhengxian Liu. 2020. "A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles" Energies 13, no. 19: 5049. https://doi.org/10.3390/en13195049

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