Design of micro radial turboexpanders for ORC power cycles: From 0D to 3D

The 3D design and analysis of a 5 kW micro turbo expanders for small, distributed ORC power units is proposed, starting from a recently developed 0D design tool, which was initially applied to 50 kWradial turbines. The turbine was sized referring to R134a as working fluid. At the same time, the main performance parameters, kinematic conditions and the different loss sources were determined. The resulting 0D basic geometry and the related non-dimensional parameters were used as the starting point to define the 3D geometry of the rotor (distribution of the metal blade angles and of the thickness profile) and to refine some design parameters like the number of blades. On the basis of the 3D blade profile and flow channels, a computational grid was generated. The CFD analysis of the rotor was carried out by means of Ansys Fluent® software, including a real-gas Equation Of State (EOS) model for the working fluid. The design of the rotor was reconsidered as a consequence of the 3D CFD approach. Finally, the comparison between the 0D and 3D results was carried out, showing a good agreement between the two approaches and, thus, verifying the reliability of the combined 0D–3D design tool for micro-size turboexpanders of ORCs.