## 6 Conclusions  
Based on a 1 MW sCO\({}_{2}\) power generation cycle, a sCO\({}_{2}\) single-stage centrifugal compressor with a speed of 40,000 RPM and a pressure ratio of 2.5 was designed. Detailed parameters and the structural design of the compressor were also given. In order to carry out compressor test, a test platform was built, and its test ability and precision could meet the requirements of the experiment. An experiment of 30,000 \(\pm\) 1000 RPM was analyzed, and the following conclusions were obtained:  
Figure 19: Curve of density with change of outlet pressure and inlet temperature.  
Figure 20: The impeller of single-stage compressor after tests.  
(a) The single-stage compressor completes about 30,000 RPM upon performance curve testing, including near the surge point and close to the choke point. The mass flow range is 13.5-18 kg/s and the maximum experimental pressure ratio is close to 2.0.  
(b) The inlet of the compressor is supercritical-liquid like, slightly deviating from the design point, and the tip clearance of the compressor is larger than the design value in order to ensure the safety of the experiment. In order to minimize the influence of the inlet condition as much as possible, the experimental results are made dimensionless by using a flow coefficient and isentropic head coefficient. The flow coefficient ranges from 0.019 to 0.025, which belongs to the small flow coefficient condition, and the maximum isentropic head coefficient is 0.46.  
(c) Comparing the dimensionless experimental curve with the design curve, it was found that the isentropic head coefficient of the experimental curve is lower than the design value, which may be caused by the increase in the tip clearance. In addition, the experimental curves shift towards the boundary of small flow coefficient, and the choke boundary becomes obviously narrower.  
(d) Condensation phenomena at the leading edge of impeller inlet were analyzed. It was found that the isentropic acceleration boundary velocity at the inlet of impeller is only 50 m/s under the experimental inlet condition, and the condensation area near the blocked boundary condition extends from the leading edge of inlet to 50% arc length. A wide-ranging condensation area occurs, and the sound velocity of two-phase fluid decreases. In addition, the condensation process was analyzed, and it was found that the average density of the liquid-like condensation process decreased, resulting in an increase in the volume flow rate and an increase in the relative speed of condensation section. Increasing relative velocity and decreasing sound velocity all aggravate local blockage of the impeller and narrow the blockage boundary of experimental curve.  
Conceptualization, Y.Z.; methodology, Y.Z.; software, Y.Z.; validation, Y.Z.; formal analysis, Y.Z.; investigation, Y.Z.; resources, X.G.; data curation, X.G.; writing--original draft preparation, Y.Z.; writing--review and editing, S.L., C.G.,Y.G. and Z.L.; visualization, Y.Z.; supervision, Y.J. and C.G.; project administration, Y.G.; funding acquisition, S.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China (Young Scientiistic Program) (52106279) and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA21010201).  
Not applicable.