Preliminary Design of Radial-Inflow Turbines for Organic Rankine Cycle Power Systems Considering Performance and Manufacturability Aspects

In order to make organic Rankine cycle power systems economically feasible, it is essential to find a reasonable trade-off between the performance and the initial cost of system. In this context the expander plays an important role. High performance is often the main target in the preliminary design of the expander; however, ease of manufacturing and competitive cost might similarly contribute to a successful solution.

The design of expanders for high efficiency and manufacturability is an unexplored field in organic Rankine cycle power systems. In this paper, we propose a multidisciplinary approach to perform the preliminary design of radial-inflow turbines for organic Rankine cycle power systems, considering both performance and manufacturability aspects.

The suitability of a turbine design is evaluated using two figures of merit: a manufacturability indicator and the turbine total-to-static efficiency. A mean-line model, estimating the turbine perfor-mance, is coupled to a model for the generation of a preliminary three-dimensional turbine geometry.

In this way, the turbine performance and its manufacturability, predicted from the turbine geometry, can be simultaneously evaluated. A multi-objective optimization is then performed using the integrated design model to optimize both the turbine efficiency and manufacturability by varying the decision variables related to its geometrical and fluid-dynamic characteristics.

In order to show its relevance in a practical application, the method is applied to two radial-inflow turbines cases: a state-of-the-art turbine using air and a turbine using the working fluid Novec 649 for a heat recovery application. The results indicate that there exists a trade-off between turbine performance and manufacturability, and that it is possible to develop turbine solutions with similar values of efficiency with improved manufacturability indicator by up to 14-15 %.