Experimental analysis of the performance of a semi-hermetic reciprocating compressor working with R744/R290 mixtures

• Semi-hermetic compressor tested with R744/R290 mixtures (5-20 % propane). • Mass flow rate decreases with increasing propane concentration. • Power consumption shows non-linear trends; reduced at high propane content. • Discharge temperature increases for R744/R290 mixtures vs pure R744. • Volumetric and global efficiencies increase for mixtures with 20 % propane. In this study, a semi-hermetic compressor designed for R744 is tested using R744/R290 mixtures with mass composition of 100/0% (pure R744, baseline), 95/5%, 90/10%, 85/15%, and 80/20%. Tests are conducted under steady-state conditions for various operating points, including different saturation suction temperatures and gas cooler pressures, with a fixed superheat of 10 K and constant compressor frequency. The results show that the refrigerant mass flow rate decreases with increasing propane content. Power consumption exhibits a complex and non-linear behavior: at low propane concentrations no clear trend is observed, whereas at higher propane contents a reduction in power consumption is measured. The discharge temperature is higher for the R744/R290 mixtures compared to pure R744. Regarding performance, volumetric and global efficiencies show no significant differences up to 15% propane, while a noticeable increase is observed at 20% propane, indicating an overall improvement in compressor performance at higher propane concentrations.