Experimental characterization and comparison of an axial and a cantilever micro-turbine for small-scale Organic Rankine Cycle

Electricity generation from waste heat by means of Organic Rankine Cycle is a promising method to increase the efficiency of industrial processes. However, due to special boundary conditions, such systems have to be robust, efficient in full load as well as in part load and scalable down to the power range of less than 15 kW. This study presents experimental results on the behaviour of two small-scale turbines, an axial impulse turbine and a radial cantilever turbine with a maximum power of about 12 kW. The turbine characteristics (isentropic efficiency and swallowing capacity) are given with respect to pressure ratio (ranging from 12 to 24) and rotational speed (ranging from 18,000 to 30,000 rotations per minute). For the axial turbine, a maximum isentropic efficiency of 73.4% has been reached in the ORC test bed. The maximum isentropic efficiency of the cantilever turbine is even higher and reaches 76.8%. The values are compared to volumetric expanders and it is shown that micro-turbines can compete even in the power range addressed in this study. As the turbine characteristics are given for full load and part load conditions, they can be implemented in simulation tools to allow for a more realistic calculation of ORCs with fluctuating heat sources.