Measurement of critical properties for the binary mixture of R744 (carbon dioxide) + R1233zd(E) (trans-1-chloro-3,3,3-trifluoro-1-propene)

Abstract

Due to excellent environmental and thermophysical properties, CO₂ has been used in many areas, such as commercial refrigeration, car air-conditioning, and heat pump drying systems in the past years. However, the low critical temperature and high critical pressure of carbon dioxide limit these applications. A potential approach to address these limitations is to create a mixture of carbon dioxide with other working fluids, such as hydrofluoroolefins or hydrochlorofluoroolefins, which exhibit lower critical temperatures and higher critical pressures. The R744 + R1233zd(E) mixture is a potential alternative working fluid. In this work, the critical properties of R744 + R1233zd(E) binary mixtures including molar composition, critical density, critical temperature, and critical pressure were experimentally measured by a variable volume system with metal bellows. The critical point is determined by judging the intensity of the critical opalescence and the reappearance of the gas-liquid phase interface. Without accounting for the fact that the purity of pure components falls short of 100 %, the combined expanded uncertainty of molar composition, critical temperature, critical density, and critical pressure is (with confidence of 0.95, k value of 2) 0.012, 50 mK, 0.6 %, and 21 kPa. The critical data obtained from the experiment are correlated with the simplified Tang et al.'s model by the Redlich-Kister approach. Both of the two fitting methods can reproduce the critical locus of the R744 + R1233zd(E) binary mixture with high precision. According to the classification of Schneider and van Konynenburg and Scott, the R744 + R1233zd(E) mixture belongs to the first class of type I mixtures, which means the critical locus is a continuous curve, and the critical pressure has a maximum value