Thermal Modelling for the Motor in Semi-hermetic Screw Refrigeration Compressor under Part-load Conditions

摘要

Semi-hermetic screw refrigeration compressor is mostly driven by a three phase asynchronous induction motor with its squirrel cage rotor attached to the shaft of the compressor helical male rotor. The motor is cooled by low temperature refrigerant coming from evaporator before it is inspired into compressor suction port. In order to investigate cooling effects of the motor and performance of the compressor under part-load conditions, a lumped parameter model describing heat transfer characteristics inside the motor and a part-load model of screw refrigeration compressor are developed. Heating effects at compressor suction end are taken into account and nodes representing refrigerant inside the motor cooling passages are modeled separately. Due to the decreasing refrigerant mass flow rate and motor efficiency, temperature rise of refrigerant through the motor increases and stator winding temperature curve goes up when the compressor load drops by suction volume variation.