Numerical Simulation of Twin-Screw Expander and Its Effect on the Performance of ORC System

For improving the expander modeling progress of the numerical simulation to get higher accuracy and obtaining its influence on the organic Rankine cycle system, this paper used a structured dynamic grid generation method based on expander rotor node mapping and a grid update technology of node migration with rotor profile to mesh by Twinmesh and Ansys and calculated the model by CFX. At the same time, the entire organic Rankine cycle system model was established. The results show that the simulation results are more suitable for the actual working process and has about 3% relative error, which is less than the reference literature results. The expander throttling loss and pre-expansion at the suction port reduce the overall performance of the expander, the leakage of tip clearance is the most serious, which should be controlled in the structure design of twin-screw expander. The indicated efficiency decreases with the increase of rotating speed and increases first and then decreases with the increase of suction pressure and discharge pressure due to over-expansion and under-expansion. The mass flow rate increases with the increase of suction pressure and rotating speed. The thermal efficiency and output power of the organic Rankine cycle system increase with increase of suction pressure and expander’s rotating speed, and decrease with the increase of discharge pressure. This paper can provide a good reference for the theoretical simulation method exploration, optimal design of twin-screw expander and organic Rankine cycle system.