Effects Of Integrated Cooling On The Performance Of Centrifugal Compressors With High Pressure Ratio

Centrifugal compressors have the benefit of producing a high pressure ratio in a smallerspace when compared with the other types of compressors. Centrifugal compressors with a high pressure ratio, have a wide application in areas which a light weight and downsized design are important and at the same time a high power output is needed. High pressure ratio centrifugal compressor is also widely used in small gas turbines. It is specially used for aeronautical applications as well as industrial applications. But the highest pressure ratio obtained by a centrifugal compressor has two limitations. High impeller temperature and the large compression power required.Thesetwo key factors limit the pressure ratio achieved by the centrifugal compressors.Cooling can be used as an effective way to reduce the required compression power and the impeller temperature.In this paper, a cooling method named integrated cooling was employed in a centrifugal compressor with a pressure ratio up to 8.0. Integrated cooling is the cooling on the external walls of compressorduring the process of compressing air. The effects of the integrated cooling on the compressor performance were studied by a threedimensional steady simulation with the conjugate heat transfer(CHT) method. Conjugate heat transfer calculation has a better prediction for the temperature profile in the solid part,comparedwith the coupled method. It is found that integrated cooling is capable of improving the compressor performance with respect to pressure ratio, efficiency, compression power as well as the impeller maximum temperature. With a cooling temperature of 300 K, the pressure ratio increased by 11.0% and efficiency by about 2.44% at the design condition. In addition, the maximum impeller temperature decreased by about 67 K.This method is more effective with a low cooling temperature and also in high rotational speed and high pressure ratio of the centrifugal compressor.In this paper, the effectiveness of the cooling on different external walls(backplate, shroud, and diffuser) is also also investigated and compared. Results show that cooling at the external walls has a considerable effect on the temperature of the impeller and the performance of the compressor. The cooling on the backplate with acoolingtemperature of 300 K reduces the impeller temperature by 67 K, whereas the cooling on the shroud and diffuser has not any effect on the impeller temperature.The cooling on the shroud and diffuser increases the polytropic efficiency by 1.5% and 1.1% respectively, whereas the cooling on the backplate has no effect on the efficiency. Furthermore, these results imply the cooling strategy should vary with respect to different design objectives. Cooling the shroud and diffuser mainly increase the efficiency while cooling on the backplate increase the reliability of the impeller.