Research on axial thrust in sCO 2 centrifugal compressors based on impeller structure

Supercritical carbon dioxide (sCO₂) Brayton cycles feature high efficiency and compact structure, which endow them with wide application potential. Nevertheless, the complicated thermophysical properties of sCO₂ bring difficulties to axial thrust control in sCO₂ centrifugal compressors during operation. This study investigates effects of semi-open and open impeller structures and operating parameters on performance and axial thrust characteristics of sCO₂ centrifugal compressor. It also analyzes influence of wheel back groove depth on axial thrust and compressor performance, and further studies combined structure of groove and balance holes on thrust balance and performance. Results show that axial thrust of impeller is mainly affected by operating parameters such as inlet pressure and rotating speed. Main reason is force change on wheel back wall. Compared with semi-open impeller, open impeller has smaller axial thrust fluctuation under off-design conditions. Back groove can adjust axial thrust distribution by changing pressure area of hub and wheel back wall. As back groove depth increases, axial balancing force first decreases and then increases. Combined with balance holes to form composite structure, axial thrust balance capacity can be improved by about 2%. However, it causes decrease in pressure ratio and isentropic efficiency, with maximum reduction of 0.46% and 1% respectively. Conclusions of this study can provide reference for axial thrust balance design of sCO₂ centrifugal compressor.