Semi-empirical model of the twin-screw refrigeration compressor with capacity control devices

Abstract

Adopting twin-screw refrigeration compressors with capacity control devices has become the dominant trend to meet varying cooling demands. To analyze the compressor performance with different capacity control methods and further explore the potential, a semi-empirical model with 16 characteristic parameters is proposed. Detailed working processes under the part-load condition (PC) are considered and the corresponding calculations, including pressure loss, power loss, and leakage are innovatively refined. Subsequently, a prototype experiment was carried out for parameters identification and model validation. A good agreement between the experimental and simulated values is attained, with average relative errors of 3.46 % and 1.15 % for shaft power and mass flow rate under the variable frequency condition (VFC) and 3.18 % and 4.63 % under the PC. Thermodynamic simulation results indicate that both shaft power and mass flow rate are linearly correlated with frequency and the efficiencies are nearly stable over the whole interval. However, as the load decreases, the performance decays significantly and the most remarkable change occurs at a position of between 0.9 and 1. The volumetric and adiabatic efficiencies of the VFC are 3.65 and 2.26 times higher than that of the PC when the mass flow rate reaches the lower limit.