Session: 37-05 Radial Turbomachinery Modelling

Paper Number: 152113

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

Compression of heavy hydrocarbons and refrigerants is an important task for a large collection of centrifugal compressors in various industrial applications. However, an overwhelming majority of applied research on the optimum design and flow field of centrifugal compressors has 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, it was developed a set of reference designs 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 to choose as baselines depending on whether peak efficiency is sought or high surge margin, depending on the application.

One of the main phenomena which describes the beginning of unstable compressor work is progress to surge or rotating stall. Operational conditions of the compressor (even if the compressor may not achieve surge, but rotating stall is beginning) can be evaluated using the surge margin on the compressor performance map.

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. Initial design of centrifugal compressor was developed and calculated in 1D/2D AxSTREAM^TM. Results analysis show good agreement between 1D/2D AxSTREAM^TM and Ansys CFX in design point for initial design, but may not satisfy off-design operational requirements for a broad range of applications. The main focus of the research is to develop a centrifugal compressor with improved surge margin by mass flow rate and by pressure. The current work includes analysis of several compressor designs and operational maps comparison between each other, and links the important design and gas dynamics variables across the operating range to characteristics of the compressor. Impeller geometry modifications, such as blade angle distribution, in conjunction with rotating speed changing have significant influence on aerodynamics parameters of compressors, can reduce blade aerodynamics loads and increase the operational range of a compressor. Additionally, the research work is focused on analysis of blade type and losses model influence on performance maps. 1D analysis and profiling of compressors cases are implemented in AxSTREAM^TM. 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 compressors inlet are constraints and are not changed. 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 has been 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 surge margin on compressor performance map by mass flow rate increases by 20% in comparison with the base value with increasing total-to-total efficiency value on design point.

Results from the research work can be used for development of refrigeration compression systems as single-stage or multistage compressors designs.

Presenting Author: Vlad Goldenberg SoftInWay Inc.

Presenting Author Biography: Vlad Goldenberg is an engineering manager at SoftInWay. His responsibilities include oversight of internal product development and commercial and government R&D projects. His interests are in the thermodynamics and fluid dynamics of advanced practical systems.

Authors:

Vlad Goldenberg SoftInWay Inc.
Ben Conser SoftInWay Inc.
Andrey Sherbina SoftInWay Switzerland GmbH
Anna Vorobyova SoftInWay Switzerland GmbH