Comprehensive assessment of the impact of operating parameters on sub 1-kW compact ORC performance

Abstract

The heat source and sink temperatures are important external variables that determine the performance of power cycles, such as the ideal Carnot cycle and Rankine cycle. In addition to these external operating variables, variations in the mass flow rate within the system can significantly change the operating characteristics of the power cycle. In this study, the combined effects of these operating variables on the compact Rankine cycle performance were investigated experimentally. A compact ORC with R245fa working fluid and scroll expander was experimentally evaluated at 100-140 °C heat source, 10-30 °C heat sink and 0.042-0.060 kg/s mass flow rate conditions.

Comprehensive experiments showed that the external parameters have significant effects on ORC operating temperature and pressure. In particular, the electrical output was well predicted by the parameter of change in the pressure difference rather than the expansion ratio of the expander. It was also found that the mechanical efficiency of expander increased nonlinearly when decreasing the heat source temperature and increasing the pressure difference of expander. The generator efficiency was not affected by the operating parameters as the expander rotational speed was linearly proportional to the electrical power. The maximum system performance showed 0.246 kW electrical output and 1.61% thermal efficiency in contrast to 0.796 kW net fluidic output and 5.72% fluidic thermal efficiency where they were in different conditions.