A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles
Journal article, 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.

maximum swallowing capacity

centrifugal compressor

supercritical carbon dioxide

impeller inlet design

condensation

Author

Xiaojian Li

Tianjin University

Yijia Zhao

Tianjin University

Huadong Yao

Chalmers, Mechanics and Maritime Sciences, Fluid Dynamics

Ming Zhao

Tianjin University

Zhengxian Liu

Tianjin University

Energies

1996-1073 (ISSN)

Vol. 13 19 5049

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Subject Categories

Aerospace Engineering

Applied Mechanics

Energy Engineering

Vehicle Engineering

Fluid Mechanics and Acoustics

Areas of Advance

Energy

Infrastructure

C3SE (Chalmers Centre for Computational Science and Engineering)

DOI

10.3390/en13195049

More information

Latest update

10/23/2020