Compressed liquid density and speed of sound measurements and correlation of the binary mixture {carbon dioxide (CO2) + 1,1-difluoroethene (R1132a)} at temperatures from 220 K to 350 K

The blend of carbon dioxide (CO2) and R1132a has been proposed as low-GWP refrigerant for low temperature refrigeration down to −60 °C, as an alternative to R23. This study provides new experimental data on the compressed-liquid density, vapour density, and compressed-liquid speed of sound for the CO2 + R1132a binary system. These measurements were obtained using a two-sinker densimeter and a pulse-echo-type speed-of-sound instrument. The density measurements span a temperature range of 220 K to 350 K and pressures up to 30 MPa with an expanded uncertainty ranging from 0.031% to 0.132%, while the speed of sound measurements cover temperatures from 230 K to 350 K and pressures up to 65 MPa with an expanded uncertainty of 0.031% to 1%. For both properties, two different mixture compositions were tested corresponding to mole fractions of CO2 equal to 0.5942 and 0.7926. Due to the strong absorption of the sound pulse by the mixture, the standard dual-path analysis could not be employed. Therefore, a method utilizing only the short-path signal was developed. Additionally, we present a mixture model based on the experimental data, derived from a Helmholtz energy model, which demonstrates a good fit with the measurements. Finally, we applied this model to compare CO2/R1132a mixtures with R23 and other alternatives. This preliminary analysis revealed the potential of CO2/R1132a as possible low-GWP and near-azeotropic refrigerants, less flammable than hydrocarbon-based mixtures and capable of providing cold at −60 °C.