Research on the Flow Field and Performance Characteristics of a Novel Reference Design Centrifugal Compressor for Refrigerant Compression

Abstract Compression of heavy hydrocarbons and refrigerants is an important task for a large collection of centrifugal compressors in various industrial applications. However, most applied research on the optimum design and flow field of centrifugal compressors relied on data gathered based on air as a working fluid. While it is recognized that dimensionless correction for gas dynamic parameters enables a broad understanding of the fundamental fluid dynamics, there are nevertheless unique attributes of machine design that are optimum specifically for heavy hydrocarbon and refrigerant type fluids. This work specifically addresses this gap. More specifically, a set of reference designs was developed for a compressor using R134a as the working fluid with boundary conditions corresponding to a typical heat pump application. The design uses an integrally shrouded impeller wheel, which is often employed in process and refrigeration compression systems. The design set we show is suited to scaling for variations in flow rate capacity and can also be employed in a multistage design. Furthermore, several variants of the design are available as baselines depending on whether peak efficiency or high surge margin is sought, depending on the desired performance. This paper describes the design strategy of a refrigeration (R134a) centrifugal compressor for achieving the best value of the surge margin and increasing the operational range of the compressor. The initial design of the centrifugal compressor was developed in 2D code and analyzed using 1D and 2D methodologies. Analytical results show good agreement between 2D code and 3D CFD analysis using Ansys CFX at the design point for an initial design but may not satisfy off-design operational requirements for a broad range of applications. The focus of the research is to develop a centrifugal compressor with improved surge margin. The current work includes the analysis of several compressor designs and the comparison of operational maps between each other and links the important design and fluid dynamic variables across the operating range to characteristics of the compressor. Impeller geometry modifications, such as blade angle distribution, in conjunction with rotating speed variability, which have a major influence on the aerodynamic parameters of compressors, can reduce blade aerodynamics loads and increase the operational range of a compressor. Additionally, the work is focused on analyzing the influence of loss models on performance maps. 1D analyses and profiling methodologies are implemented using 2D code. The meridional geometry of the impeller, vaneless diffuser, and volute are maintained through the design variations such that components can be substituted in application. Additionally, boundary conditions at the compressor inlet are fixed. All compressor designs have unique attributes that contribute to, or may be attributable to, specific characteristics of their performance. Verification of the performance map and surge margin was carried out using the commercial CFD code Ansys CFX and compared with results from 1D/2D analysis and tuned to well-known models. This results in a 10% increase in mass flow rate-based surge margin. Results from the research can be used for the development of refrigeration compression systems as single-stage or multistage compressors designs.