A 1D Model to Predict the Efficiency of Radial Inflow Turbines in Organic Rankine Cycle (ORC) Systems: preliminary results

The favorable thermodynamic properties of organic fluids make Organic Rankine Cycle (ORC) systems the best option for power generation from low‐to‐medium temperature heat sources due to the lower heat transfer irreversibilities and higher efficiencies compared to steam power systems. The lack of extensive experimental data on the efficiency of turbines operating with high molecular weight fluids makes turbine design a very challenging task. In this work the results obtained by a mean‐line model of single stage radial inflow turbines (RITs) operating with R245fa are presented. The model takes into account the real gas properties and is organized into two main consecutive steps: the “design routine” and the “performance routine”. In the former the turbine geometry is defined starting from the cycle design specifications and non‐dimensional parameters (velocity ratio and specific speed). In the latter the turbine efficiency is calculated using the loss correlations specifically developed by Aungier (2006) for radial inflow turbines. The results obtained at different cycle design specifications and nondimensional parameters provide a clear indication of their influence on the efficiency of single stage radial inflow turbines for ORC systems. Thus, design guidelines for the optimum design of ORC RITs are proposed.