One-dimensional optimisation design and off-design operation strategy of centrifugal compressor for supercritical carbon dioxide Brayton cycle

The advanced supercritical carbon dioxide Brayton cycle has received significant attention in the field of renewable energy. However, the commonly used modeling method of a constant-efficiency compressor cannot predict the unknown off-design behavior of the system caused by the compressor inlet temperature change, which makes the one-dimensional design and analysis of the compressor necessary. In this study, the accuracy of the developed one-dimensional design and analysis model was verified against the performance experimental data of two types of centrifugal compressors. After discussing the geometric sensitivity of the compressor, the optimisation design of the centrifugal compressor in the supercritical carbon dioxide Brayton cycle was conducted using a genetic algorithm. Moreover, the off-design behaviour of the system induced by climate change was assessed, and countermeasures for its low performance were proposed. The comparison shows that the deviation of the one-dimensional design model is within 10%, and the analysis model with a deviation of less than 5% can effectively capture the trend of the compressor performance curve. The parameter analysis discovers that the compressor optimal head coefficient of 0.53 corresponds to the maximal cycle efficiency of 24.40%. The system off-design efficiency of 27.35% at the compressor inlet temperature of 304.15 K is higher than 18.88% at 310.15 K, which suggests that the operating time of the supercritical carbon dioxide Brayton cycle should be longer in winter than in summer. Meanwhile, increasing the compressor inlet pressure and raising the speed are two strategies to improve the poor system performance of the summer by more than 25%, and the first strategy also broadens the high-efficiency range of the compressor inlet temperature to 4 K. This study can provide guidance for improving the off-design behaviour of the supercritical carbon dioxide Brayton cycle resulting from changes in ambient temperature.