Preliminary design and numerical analysis of a radial inflow turbine in organic Rankine cycle using zeotropic mixtures

Abstract

Turbine and the working fluid are two key factors that affect the performance of an organic Rankine cycle (ORC). A one-dimensional design for an ORC radial inflow turbine is conducted in this paper. An entire three-dimensional model of the designed turbine including the nozzle, rotor, and volute, is developed and its performance is predicted by Computational Fluid Dynamics. Peng-Robinson equation is employed to predict the properties of working fluids. The simulation shows that the numerical results agree well with the designed value. Additionally, the performance comparison between R245fa and R245fa/R134a is carried out. It is concluded that when R245fa and R134a are mixed with a ratio of 7:3, the power output and isentropic efficiency of the turbine are 9.3% and 2.5% higher than pure R245fa, respectively. What’s more, the off-design performance of the radial turbine using R245fa/R134a is numerically investigated. The results show that there is little change for isentropic efficiency of the radial inflow turbine when the rotational speed varies from 95% rpm to 115% rpm. However, the pressure ratio has a great impact on turbine efficiency. The performance prediction method based on preliminary design and numerical simulation can be applied to the future optimal design of a radial-inflow turbine using zeotropic mixture fluids.