Evaluating a Meanline Model for Partially Admitted Axial Turbines Operating in Organic Rankine Cycles: Extensive Experimental Validation with Multiple Working Fluids and Mixtures

This study aims to evaluate the robustness of the well proved Aungier meanline model, originally developed for air and steam turbines, on Organic Rankine Cycles (ORC) turbines. More specifically, the study focuses on two pure-impulse axial turbines with partial admission and using various working fluids, including zeotropic mixtures. To this end, a three-part numerical model was developed to adapt this type of meanline model to a prediction-oriented methodology rather than a design-oriented one. Using inlet and outlet pressures, inlet temperature, and rotational speed as inputs, the model provides the resulting mass flow rate through the turbine as well as its performance characteristics. The model predictions are compared against an extensive experimental dataset comprising more than 300 operating points obtained with three pure fluids—R1233zd(E), NOVEC™ 649, and HFE7000—and three zeotropic mixtures. The model demonstrates good predictive accuracy over a wide range of operating conditions, including very low velocity ratios corresponding to severe off-design operation. Specifically, the mass flow rate is predicted with a Mean Absolute Percentage Error (MAPE) ranging from 1.23% to 3.31%, depending on the working fluid. Furthermore, over an experimental specific work range of 5 to 15 kJ/kg, the predicted numerical work exhibits a MAPE of 7.04% for 102 experimental points corresponding to the main dataset (R1233zd(E)). Finally, the total-to-total efficiency is predicted within ±4 efficiency points, showing a very good trend over a velocity ratio range from 0.06 to 0.36.