Effect of flow channel structures and refrigerants on the motor cooling process of compressor with gas bearings

Abstract

Energy-saving and environment-friendly water chiller is the development trend. The efficient compressors and new refrigerants are hot spots. The gas bearing can significantly improve the performance of centrifugal refrigeration compressors, and effective motor cooling is the guarantee of performance and reliability. The influence of channel structure and refrigerant on the performance of the motor cooling process and refrigeration system is analyzed. The results show that adding the bearing gas supply circuit decreases the motor temperature and the maximum variation of permanent magnet temperature is about 60 °C. The cooling channel structure in the interlayer of the motor shell will affect the cooling process. The spiral channel can reduce the stator temperature and improve the uniformity of temperature distribution. But the temperature of the motor changes slightly when the length of the channel is more than 6000 mm. The motor temperature is the highest with refrigerant R1234ze(E), followed by it R1234yf and R134a. The maximum temperature of the permanent magnet for R1234ze(E) is 20–50 °C higher than it for R1234yf and 50–60 °C higher than it for R134a under different inlet diameters. The maximum temperature of the permanent magnet for R1234ze(E) is 30 °C higher than it for R1234yf and 50 °C higher than it for R134a under different inlet temperatures. The system with a motor cooling circuit has controlled the motor temperature within the safe operation range, while the COP of systems with R134a, R1234yf, and R1234ze(E) has only decreased by 4.63 - 5.36%, 4.22 - 4.6%, and 3.78 - 4.15% respectively.