Design and optimization of a radial-axial two-stage coaxial turbine for high-temperature supercritical organic Rankine cycle

High-temperature supercritical organic Rankin cycle (SORC) has great application potential but has not been fully studied. To achieve a large expansion ratio in the high-temperature SORC system, a radial-axial two-stage coaxial turbine with Siloxane MM as working medium is designed and optimized in this paper. This newlystructured turbine, which has simple and compact structure and relatively light weight, is more suitable for large commercial ORC system with medium-high temperature. The whole design flow of this turbine is described, including input, design, optimization, modeling and simulation processes. The turbine performances at both design and off-design conditions are discussed. The total-to-total isentropic efficiency of 86.55% is achieved at the expansion ratio of 15.37 and it can also maintain at a relatively high level within a wide range of expansion ratio and rotating speed. The results prove that the proposed methodology can be applied to designing the radial-axial turbine for SORC system. The turbine configuration and the design method proposed in this study can provide the reference for the research and development of high-power SORC turbine.