Experimental Investigation on the Performance of a Twin-screw Expander Used in an ORC System

Organic Rankine Cycle (ORC) is an effective and promising technology to convert low-grade thermal energy to electricity. As a key component in an ORC system, the expander plays a significant role in energy conversion efficiency in the ORC system. In this paper, an ORC experimental system is developed to investigate the performance of a twin-screw expander under various working conditions. Pressure sensors with high sensitivity and accuracy are installed at appropriate locations in the expander casing to monitor the p-V (pressure-volume) indicator diagrams which indicates the performance of the expander. The effect of the key parameters such as expander rotating speed, the suction pressure on the expander performance is studied using the experimental data. The results show that high expander rotating speed leads to large suction pressure loss, low volumetric and indicated efficiencies. As the rotating speed increases from 900 rpm to 1900 rpm, the volumetric efficiency decreases by up to 17.2% from 1.004 to 0.831and the indicated efficiency reduces by up to 27.1% from 0.846 to 0.617. Furthermore, as the suction pressure increases from 550 kPa to 750 kPa the indicated efficiency rises up to a peak value of 0.815 and then falls. The volumetric efficiency does not show significant change as the suction pressure varies.