Design of radial turbomachinery for supercritical CO2 systems using theoretical and numerical CFD methodologies

In high temperature waste heat to power conversion applications, bottoming thermodynamic cycles using carbon dioxide in supercritical phase (sCO2) have recently become a promising developing technology that could outperform conventional Organic Rankine Cycle systems in terms of efficiency and compactness. Moreover, carbon dioxide is a fluid chemically stable, reliable, low-cost, non-toxic, non-flammable and readily available. Supercritical CO2 power generation systems have been investigated by scientists and engineers mostly for large scale applications. However, when the electrical target output power is lower (50-100 kW), there are additional challenges on the turbomachinery design that need to be addressed. In the current research work, with reference to simple regenerative cycle architecture, the design of small scale sCO2 radial compressor and turbine are firstly addressed through the similarity approach. Further to this study, numerical CFD simulations are performed to optimize the 3D design of the impellers and of the stators. In particular, steady state RANS simulations using the mixing plane approach are carried out taking into account real gas properties for CO2.