ORC, Twin-screw expander, p-V indicator diagram, Suction pressure drop, Efficiency
Organic Rankine Cycle (ORC) is an effective and promising technology to recover low-grade waste heat and output electricity. As a key component in an ORC system, the expander’s performance significantly affects the whole system’s efficiency. Twin-screw expander is widely employed for its compact structure, reliability, two-phase tolerance and high efficiency. To investigate the characteristics of twin-screw expander, a test bench was set up in a laboratory taking 120 waste steam as heat source. R245fa was selected as the working fluid. Pressure sensors with high sensitivity and accuracy were installed at appropriate locations in the expander casing to monitor the p-V indicator diagrams. The expander’s p-V indicator diagrams and operating parameters were recorded under different operating conditions. The effects of rotational speed and suction pressure on the expander’s suction pressure drop, volumetric efficiency and indicated adiabatic efficiency were studied. Results show that rotational speed and suction pressure affect the suction pressure drop altogether, which has a significant effect on the density and mass flow rate of the sucked gas. The expander volumetric efficiency is above 85% and the indicated adiabatic efficiency can also reach 82%.