Abstract: Steam compressor shows great energy-saving potential in mechanical vapor compression, desalination and high temperature heat pump in all industries. With water injection, high exhaust temperature can be avoided and the compressor performance will be enhanced. A thermodynamic model was developed for the real working process in water injected twin-screw compressor. Heat and mass transfer between the compressed vapor and injected water were considered altogether with leakage. The errors between simulated and experimental results were within ±5%, which proves the proposed model efficient for performance prediction. The effects of injected water flowrate and rotating speed on the compressor performance were investigated. Results indicate that water injection can efficiently improve the compressor performance. Compared with zero injection, the volumetric efficiency and isentropic efficiency can be improved by 11.9% and 17.2% respectively under certain conditions. Moreover, there exists an optimal flowrate of injected water which increases linearly with rotating speed. The optimal mass ratio of injected water also slightly increases with rotating speed, which remains about 8.9%~10.4% for the investigated compressor. With the increase of suction pressure, the compressor efficiency drops quickly due to larger leakage, which needs further illustration.

Key words: twin-screw compressor, steam, water injection cooling, heat and mass transfer