Centrifugal Compressor Performance Deviations with Various Refrigerants, Impeller Sizes and Shaft Speeds

Under the pressure of the Montreal Protocol originally written in 1987, the current popularly used HCFC and HFC refrigerants for comfortable air conditioning, such as low pressure refrigerant R123, will have to be phased out in the near future. This forces companies in centrifugal chiller industry to redesign and retest new centrifugal compressors which can accommodate alternative refrigerants. Keeping the present flow path designs is an economic design process for the alternative refrigerants, and is well adapted by companies in this industry. In addition extensively employ the flow similitude theory is also an effective way to minimize the cost of lab tests. However employing similitude in compressible flow does not forecast the content in which compressors meet the uncontrollable situations such as choke and surge. Conclusions can only be drawn from experimental data [Dixon, Ferguson]. This paper will present the theory and experimental verification for a low cost method to predict the compressor performance under an alternative refrigerant based on existing compressor maps. A few factors that affect compressor performance maps, but whose effects cannot be predicted by similitude theory are also analyzed by reviewing large amount of tested data