With increasing environmental awareness

natural refrigerants have regained prominence. An air-cycle refrigeration system is an effective alternative because air is harmless and environmentally friendly. The expander-compressor system is the core component of an air-cycle refrigeration system

where the compressor input power varies with the expander performance curve. To design a centrifugal compressor that can operate efficiently with an expander

modifications to traditional design methods are required. By combining the conservation of mass

momentum

and energy with the jet wake flow pattern and extending the relevant parameters of the traditional centrifugal compressor to a lower pressure range

a design method for matching the geometric parameters of a centrifugal compressor with an expander is proposed. This method was applied to design a centrifugal compressor corresponding to an existing expander

which was validated using a centrifugal compressor model previously analyzed by other researchers. Computational fluid dynamics (CFD) was employed to simulate and assess the operational performance of the expander-compressor under variable operating conditions

including the utilization efficiency of the expansion power. A centrifugal compressor designed using this method achieved more than 92% and 88% utilization efficiency under the nominal operating condition and variable operating condition

respectively. The expander functioned smoothly within the designed mass flow rate range.