Rotating Shaft Thermal Analysis for Supercritical Carbon Dioxide Radial Inflow Turbines

Supercritical carbon dioxide (sCO) in power cycles has been shown to have high efficiencies at high temperatures. Good heat transfer properties and high power density reduce cycle complexity and component size when compared with conventional steam cycles. A key design challenge with sCO turbomachinery is the reduced size due to the high power density. This is particularly true for radial inow turbines which are currently more common in low power output applications. This results in reduced space between critical components, requiring a thermal management strategy for safe operation. This paper presents and analyses an active cooling system for the main rotor shaft in a radial inow turbine operating with sCO and utilizing sCO as the cooling fluid. A coupled thermal-fluid-structural heat transfer analysis is conducted. Predicted temperature distributions show that large temperature differences can be achieved over short lengths due to the high convective heat transfer coefficients of sCO under these flow regimes. Performance trends of the cooling system with respect to cooling fluid mass flow rate and coolant inlet temperature are presented.