Aerodynamic Design of Refrigeration Compressor for Optimal Range and Efficiency

Abstract There is an increasing trend in using oil-free centrifugal compressors in refrigeration chillers and heat pumps for superior efficiency, lower maintenance, and reduced lifecycle costs. Centrifugal compressors for chiller application are subjected to wider operating range when compared to those used in many other applications. While numerous aerodynamic and numerical design tools are either commercially available or developed by specific manufacturers and/or research institutions, designers face significant challenges in choosing appropriate design attributes and dimensions of flow path components, especially when additionally constrained by stagewise performance, bearings, rotordynamics, and overall layout. This paper demonstrates how commercially available design and analyses tools are used to perform aerodynamic design and optimization of aerodynamic flow-path of a refrigeration centrifugal compressor to enhance operating range and aerothermal efficiency while maintaining pressure ratio or chiller capacity within expected operating regime. Relevant details of one-dimensional (1D) and two-dimensional (2D) design are shown along with some details of three-dimensional (3D) numerical (CFD) analysis. This paper also illustrates how selection of various components and overall layout influences design and aerodynamic optimization of the impellers. Numerical analysis is also performed to optimize axial thrust for the pair of opposed configured impellers mounted on the same shaft. Moreover, the same numerical model provides superior insight about overall performance impact for the presence of shaft seals or secondary flow paths. Finally, test findings at the in-house test facility are shared to compare overall performance of the original and the modified compressor.