Thermal and hydraulic analysis on the flow around the motor in semi-hermetic twin screw refrigeration compressors

• Thermal behavior of the motor in semi-hermetic refrigeration compressors was studied.
• A comprehensive model was developed for this purpose and experimentally validated.
• A semi-hermetic twin screw refrigeration compressor system was set up.
• The experimental validation was performed under various operating conditions.
• The effect of the motor geometry on temperature in the motor winding was investigated.

A comprehensive model was developed to study the flow and thermal behavior of the motor cooled by suction refrigerant in semi-hermetic twin screw refrigeration compressors. The model is sufficiently complex to consider the special motor features, including: refrigerant flow characteristics and thermal heating caused by electrical losses; heating effect of oil from bearings and gas-oil mixture from the bypass port. The model was experimentally verified under various operating conditions. The stator winding temperatures and refrigerant thermal property variations were measured and compared with the calculated ones. The results show that our model can accurately predict the temperature distribution inside the motor. Further, this validated model was used to investigate the effects of cooling passage arrangement on temperature distribution inside the motor. It was found that the dimension and shape of the stator cooling duct has a large effect on the temperature inside the motor while the effect of the inner diameter of rotor cooling holes is negligible.