Unsteady flow and thermal dynamic performance of pre-compression characteristics in variable-speed scroll compressors

•3D unsteady internal flow of pre-compression was revealed.•Effects of variable rotational speed on pre-compression were investigated.•Validation of the pressure distribution was performed with experimental data.•The thermodynamic characteristics produced by pre-compression were presented. In the suction process of scroll compressors, a special thermodynamic phenomenon occurs, known as pre-compression, which significantly affects the inhalation capacity, volumetric efficiency, and thermal characteristics of scroll compressors. To explore its generation and impact, unsteady flow field distributions of the pre-compression phenomenon were obtained by numerical simulations. The pressure variation of the pre-compression phenomenon in air was analyzed, and the power consumption caused by pre-compression during the working process was investigated. Study results indicated that the pre-compression phenomenon is mainly produced by the geometric structure and operating features of the scroll compressor. The initial angle of the pre-compression phenomenon decreases by 31° as the rotational speed ranges from 3000 to 7000 r/min. The generation of the pre-compression phenomenon induces eddies in the suction chamber. Additionally, it was demonstrated that during the suction process, mass flow rate increases owing to the pre-compression phenomenon. The study is helpful for analyzing the suction process and improving operating efficiency of scroll compressors.