Performance investigation of a two-stage partial admission axial impulse turbine used for low temperature organic rankine cycle

Turbine was one of the commonly used expanders in organic Rankine cycle. High Mach number shock wave losses and high rotating speeds were the main problems for low-power ORC turbines. In this work, a two-stage partial admission impulse turbine was adopted to reduce shock wave loss and lower the optimal rotating speed. The performance of the two-stage turbine was studied through mean-line analysis and numerical simulation. Results showed that the maximum power of the two-stage turbine was 6.3 % higher than that of the single-stage turbine and the optimal rotating speed was reduced by 22.2 %. An optimal number of blades could reduce flow losses and improve turbine efficiency. The second stage partial admission rate (e2) affected the flow capacity and expansion ratio of each stage. When e2 = 0.06, the power outputs of the two stages were basically equal. The blade located at the boundary of the admission and non-admission sections had a large negative power if the pressure surface was in the non-admission section. The relative clocking angle between the first-stage nozzle and second-stage stator affected both the mass flow rate and power output. The total power output was the highest when the clocking angle was 0°.