Effects of different working fluids on the performance of a radial turbine in an organic Rankine cycle power system

Abstract

Organic Rankine cycle (ORC) power systems are widely used for low-temperature heat recovery. The radial turbine is the most important component in the ORC system and its performance is significantly dependent on the working fluid. Therefore, the effect of different working fluid on the performance of radial turbine in ORC system for the low-temperature heat source (120~180 °C) was investigated. First, the feasibilities of different working fluids for 150 kW radial turbine using R600a as designed working fluid were investigated. The thermal aerodynamic calculation of R600a at design condition was conducted with evaporation temperature 95 °C and condensation temperature 38 °C. The operation parameters of 5 non-designed working fluids (R600, R245fa, R245ca, R123 and R601a) were selected in the same temperature variation range as R600a. Then, the performance of a radial turbine for six working fluids at design condition was analyzed, and their three-dimensional flow field performances were also obtained by CFD numerical simulation. Finally, to broaden the operation range of the radial turbine and investigate the matching relationship between operation parameters and different working fluids, the off-design performances of radial turbine using six working fluids were analyzed and the effect of rotation speed, inlet pressure and inlet temperature on the performance of radial turbine was obtained. Results show that the performance of the radial turbine using the designed working fluid R600a is the best with efficiency of 82.7 % and output power of 150.5 kW. For the non-designed working fluids, the comprehensive performance of R600 was also judged to be good owing to the highest efficiency (85.1 %) and a relatively high power output (115.8 kW) among the fluids tested. For other working fluids, the output power of the radial turbine decreased obviously. There exists an optimum rotation speed for different working fluids to ensure that the radial turbine has the highest efficiency. The inlet pressure has a larger effect on the performance of the radial turbine than that of the inlet temperature. The results can provide basic data for the optimization design and operation of radial turbines in the ORC system.