Experimental evaluation of natural CO2-based mixtures with hydrocarbons R290 and R1270 in a transcritical refrigeration plant

In light of the low performance of the basic CO₂ transcritical refrigeration cycle, this study explores several CO₂-hydrocarbon blends to enhance the Coefficient of Performance (COP) and, consequently, minimise the cycle's electrical power consumption. Based on a single-stage cycle with IHX four blends of carbon dioxide/propylene (CO₂/R1270) and carbon dioxide/propane (CO₂/R290) (96/4 %_mass and 94/6 %_mass each) were tested at identical operating conditions rejecting heat to three temperature levels (20, 27, and 34 °C) with similar cooling demanding conditions (0 °C). Test results revealed COP improvements at transcritical conditions up to 9.7 % using a 4 %_mass of R1270 and up to 4.7 % with a 6 %_mass of R290. Furthermore, by adding 4 %_mass of R1270, the resulting mixture increases the cooling capacity from 2.3 to 5.8 % regardless of the heat rejection temperature. Finally, the compressor power consumption showed a significant reduction from 1.2 to 7.4 % compared to pure CO₂, mainly due to improved compressor efficiencies by mixtures. The results demonstrate the convenience of using CO₂ – hydrocarbon mixtures as drop-ins to replace pure CO₂ in existing transcritical plants.