Design optimization of partial admission axial turbine for ORC service

• A loss model for the flow through the axial blades of a turbine is proposed in this paper.
• The application of a single stage partial admission turbine in organic Rankine cycle is analyzed.
• A design optimization procedure is presented, aiming the best possible performance.
• Simulation results show that stage performance is highly influenced from media compressibility.

An analysis of the application of a single stage partial admission axial turbine in organic Rankine cycle is presented. The cycle is utilized to recover the heat rejected by an internal combustion engine. The selected fluid is R245fa, whose real gas behavior is relevant under the studied conditions, as modeled by the Redlich–Kwong–Soave equation of state. A loss model for the flow through the axial blades is proposed in this work based on the boundary layer theory, the concept of diffusion factor, wind tunnel cascade tests available in literature and the conservation equations for compressible flow. The basic geometry and dimensions needed to achieve maximum turbine efficiency are determined under several subcritical and supercritical cycle conditions by means of a restrained design optimization algorithm. The single stage turbine preliminary design is shown to be greatly influenced by media compressibility and the use of convergent-divergent profiled nozzles is promising to achieve the highest possible performance potential, especially at high evaporator pressure conditions.