Axial flow turbines for Organic Rankine Cycle applications

This chapter aims to define a set of general correlations for the estimation of axial-flow turbine efficiency in the Organic Rankine Cycle (ORC) field. A dedicated numerical tool is used for the optimization of several hundreds of turbines and the results are presented in terms of specific parameters (SP, Vr, and Ns) according to similarity rules. The analysis is carried out for single, two, and three stages turbines. For each case a correlation of efficiency at optimal rotational speed is calibrated in function of the equivalent single stage SP and the total isentropic Vr. Three sensitivity analyses are proposed in order to highlight the effects of each single parameter on stage efficiency. Finally, the effect of fluid choice on turbine performance and dimension is discussed with a numerical example.