Thermodynamic analysis of open-air Brayton cycle to predict radial turbine aerodynamic performance

The separated performance evaluation of the system and turbine leads to low accuracy in overall system performance prediction for the open-air Brayton cycle. To achieve the coupling analysis of system and turbine performance prediction and improve the accuracy of parameters optimization, this paper focuses on the improvement of the system and turbine performance evaluation approach. An improved turbine design approach based on blade loss coefficient correction is proposed to promote accuracy in turbine design. Meanwhile, an improved system-turbine coupled evaluation method for the open-air Brayton cycle is established by coupling the system performance prediction with the improved turbine design approach. The overall system performance analysis of the open-air Brayton cycle is performed to present the superiorities of the improved system-turbine coupled evaluation method. Furthermore, the parameters optimization of turbine design is carried out with the system performance evaluation and the rotational speed consideration to obtain optimum turbine isentropic efficiency. The results indicate that the improved turbine design approach can significantly decrease the relative error of turbine isentropic efficiency in one-dimension design to less than 1.85%. The improved system-turbine coupled method can decrease the relative deviation by 12.96% in system thermal efficiency compared with the conventional approach. In addition, the higher residual velocity loss, the lower disk friction loss, and the higher blade velocity coefficient are caused by the higher turbine rotational speed. Ultimately, the maximum thermal efficiency of the open-air Brayton cycle is 40.35% and the corresponding optimum turbine isentropic efficiency is 89.14% under the given system conditions. It is of great significance for parameter setting and optimization for the open-air Brayton cycle, and offers the support for the energy sustainability utilization.