Development and dynamic characteristics of an Organic Rankine Cycle

Abstract

The design, construction and test of an Organic Rankine Cycle (ORC) with R123 as the working fluid were performed. A scroll expander was integrated in the system. The conductive oil with its temperature of 150 °C was used to simulate the low-grade heat source. An AC dynamometer unit measured the expander shaft torque, rotating speed and shaft power. The experiments were conducted in two operating modes: the constant mass flow rate and the constant shaft torque. Under the constant mass flow rate operating mode, the stepped increase of the shaft torque increased the expansion ratios of the expander and decreased the vapor superheats at the expander inlet. Thus, the shaft power and thermal efficiency were increased. Alternatively, the constant shaft torque operating mode involved two different regions, interfaced at the pumping frequency of 9 Hz. By the increase of the mass flow rates, the vapor superheats at the expander inlet was decreased and the shaft power was increased, but the ORC thermal efficiencies were slightly decreased. Both operating modes yielded the saturation shaft powers that were the maximum values one could use. It was found that the measured shaft powers and ORC thermal efficiencies were lower than the enthalpy determined values based on the fluid pressures and temperatures at the expander inlet and outlet. The maximum measured shaft power and thermal efficiency were 2.63 kW and 5.31 %, compared with the enthalpy determined values of 3.87 kW and 9.46 %, respectively.