Design and Experimental Study of a 5-kW Organic Rankine Cycle with Axial-Flow Turbine for Low-Temperature Heat Recovery

Abstract

The microscale organic Rankine cycle (ORC) system is considered a promising technology to recover thermal energy from widely distributed low-temperature heat sources. By using HFC-R225fa as working fluid, a 5-kW low-temperature ORC system with a hermetic axial-flow turbo generator was designed, and performance of the ORC system was analyzed based on the experimental data. During the design period, the actual electric power output of the ORC system was 2.5 kW, and the internal efficiency of the axial turbine was 23.6%. However, it was found that at the turbine rotational speed of 16, rotation per minute (rpm), such aforementioned performances are reduced to approximately half of the design values. Hence, the disagreement between the design value and experimental data implies that the conventional axial turbine design model is inaccurate at low turbine rotational speeds, and the thermal energy grade is decreased in the generator coil cooling process of the microscale integrated turbo generator structure. The experimental results also showed that the axial turbine performance is improved at high turbine rotational speed for the microscale ORC system. Finally, a suitable turbine rotational speed is recommended in this research.