Multi-objective optimization of the ORC axial turbine for a waste heat recovery system working in two modes: cogeneration and condensation

Due to the demand of the district heating network and electric power grid ORC turbines can operate in the condensation and cogeneration modes. This approach requires the design of an expander which is characterized by high efficiency in each mode of operation. The paper is devoted to a multi-objective efficiency optimization of a one stage axial ORC turbine working on MM (Hexamethyldisiloxane). An Implicit Filtering algorithm (IF) is used to find a flowpath with maximum efficiency. During the optimization the rotor profiles (at the hub and shroud) and the shape of endwall contours of the rotor domain are changed. Five optimization tasks are carried out with different weights of the efficiency of both modes of operation. Pareto fronts are obtained and a decision-making method is used to select an optimum solution. The optimization of the rotor row allows for significant efficiency improvements in two regimes of operation, with respect to a baseline geometric configuration designed with the help of classical methods. •A methodology for multi-objective optimization of a turbine was described.•The process was carried out for five different objective function formulations.•The optimum flowpath geometry was found based on Implicit Filtering algorithm.•The Pareto optimum improved the total-to-static efficiency by 3.1 pp. and 4.8 pp.