Design and optimization of micro radial inflow turbine for low thermal organic Rankine cycle using the preliminary design method

Radial Inflow Turbines (RIT) in Organic Rankine Cycle (ORC) systems are an effective solution for low- temperature, small-scale applications due to the robust nature of these turbines. Turbines represent a substantial portion of the investment costs in ORC systems, necessitating the development of low-cost design and optimization methods. This study focuses on the optimization of a 10-kW radial inflow turbine, using R245fa as the working fluid and employing a Preliminary Design (PD) method. Five design variables were optimized: work coefficient, flow coefficient, axial height ratio, rotational speed, and outlet radius ratio to maximize total-to-static efficiency. The optimized design achieved a total-to-static efficiency of 80 % and produced 10,024 W at a rotational speed of 35,000 rpm. The CFD model has been validated by using T-100 experimental and design data. Several 3D CFD simulations were conducted over a range of rotational speeds from 20,000 to 40,000 rpm, showing a maximum deviation of 0.3 % in efficiency and 0.2 % in power output compared to the PD method. Under off-design conditions, the turbine's efficiency reached 83 % at an expansion ratio of 4 and 38,000 rpm, with a maximum power output of 19,857 W. A high-loading region was observed at the rotor's leading edge, with pressure fluctuation at the 0.1 streamwise region, requiring further optimization near the trailing edge. This methodology proved effective in designing efficient turbines for micro-ORC systems across a broad range of operational conditions.