Performance evaluation of a partially admitted axial turbine using R245fa, R123 and their mixtures as working fluid for small-scale organic Rankine cycle

•Turbine is designed and analyzed with zeotropic mixtures.•Turbine has the maximum mass flow gain and power output gain when x = 0.25.•The maximum power output and efficiency of turbine are 8.1336 kW and 55.6%.•ORC performances are evaluated coupling with the designed turbine. Zeotropic mixtures and turbine expander were two hot topics in organic Rankine cycle (ORC) field recently. However, few researches referred the design of turbine expander with zeotropic mixtures. In this paper, R245fa, R123 and three mixtures (0.25R245fa/0.75R123, 0.5R245fa/0.5R123, 0.75R245fa/0.25R123) are used as working fluid to investigate the performance of a partially admitted turbine consisting of 3 nozzles and 30 blades. The mean-line diameter of turbine is 0.1 m and the height of blade is 14 mm. The 3D simulation are carried out with ANSYS CFX using k-omega turbulence model and SRK real gas model. Results show that turbine has maximum power output of 8.1336 kW and maximum efficiency of 55.3% with pure R245fa used as working fluid. When the mass fraction of R245fa is 0.25, mixture has the maximum glide temperature of 3 K, while turbine has maximum power output gain of 7.87%, maximum mass flow rate gain of 3.57%, maximum Ma number of 2.19 and maximum mass flow rate of 0.5287 kg/s. The results of system analysis coupling with the designed turbine show that the maximum thermal efficiency, maximum net work and minimum exergy destruction factor are 6.15%, 7.6771 kW and 2.41 respectively for the best working condition.