High Specific Power on a Small-Scale Turbine

In this study, a mixed-type turbine was designed and tested with the double or single stage to improve the specific torque when it operates at a low partial admission rate. The turbine consists of double stages, and the outer diameter of its rotor is 108 mm. The turbine rotor blades were designed as an axial-type blade along the mixed flow direction because the partial admission rate was 1.7-2.0% depending on the flow direction. Performance characteristics were measured at the double and single stage rotors to investigate the effect of the second stage on the low partial admission. In addition, when the flow direction was radially inward or outward at the nozzle, turbine performances were studied. In this experiment, the specific power, torque, and total-to-static efficiency were measured at various rotational speeds to compare with the turbine performance according to different operating condition. The tested results showed that the second stage should be adopted to increase the operating torque when the operating rotational speed was less than the critical rotational speed. The specific torque was improved by 7.8% using the second stage at a radially inward flow direction turbine.