Effect of internal losses on the thermodynamic performance of a supercritical carbon dioxide Brayton cycle system

The supercritical carbon dioxide Brayton cycle, as a promising next-generation power cycle, has the advantages of high efficiency and small size, while now exhibits actual operating efficiencies significantly lower than those predicted by theoretical models. In this study, a steady-state analysis model of the supercritical carbon dioxide Brayton cycle is developed to investigate the impact of internal losses, including pipeline pressure loss, leakage reinjection, and turbine cooling, on the overall system performance. Through evaluations under both design-point and off-design operating conditions, it is found that internal losses markedly degrade system efficiency. Specifically, the efficiency loss due to internal losses increases with rising turbine inlet temperature and working medium mass flow rate, whereas it decreases with increasing compressor outlet pressure. Exergy analysis further reveals that internal losses reduce the net power output and increase system exergy losses, primarily due to enhanced exergy losses in components such as pipelines, auxiliary heaters, compression pumps, and coolers. Quantitative assessment indicates that the influence of internal losses varies under different operating conditions. Among them, pipeline pressure loss has the most significant impact on system performance at design conditions, followed by turbine cooling, while the effect of leakage reinjection is relatively minor. This study provides insights that can support more accurate modeling, improved system design, and performance optimization of supercritical carbon dioxide Brayton cycle systems.