Performance Gain for Multiple Stage Centrifugal Compressor by using non-Equal Impeller Configuration

Multi-stage centrifugal compressors, used for air-conditioning applications, are traditionally designed to have near-identical impeller tip diameters.  This kind of design can ensure even work delivered into refrigerant gas by each stage.  This design simplification may have profound drawbacks on compressor efficiency, especially for chillers using an economizer cycle, where each stage of compression deals with an increasing mass flow rate. For those multiple stage centrifugal compressors connected with economized cycle chillers, the flow of the later stage of the compressor is merged with the flow from the economizer. Therefore, the flow rate for each stage will be much different at any given time. Non-equal impeller diameters will thus show performance advantages.  A possible reason for benefit of non-equal diameters is to put more work into higher efficiency stages.  This paper will show that, by removing this design constraint and judiciously size each stage tip diameter, compressor efficiency can be improved by ?.?% (TBD in final draft, possible value is about 2.4%) on average. Analytical studies, based on Euler power, and laboratory experiments have both validated these gains. By extensively using geometric similarity, the proposed methodologies are also applied to other compressors in the same family and similar performance improvement can be achieved.  Since the non-equal impeller designs extensively use the existed impeller map data its design lead time is considerably shorten. Â