Measurement of critical parameters for the binary mixture of R744 (carbon dioxide) + R1234yf (2,3,3,3-tetrafluoropro-1-ene)

The critical parameters including critical temperature, critical pressure, critical densities, and mole fraction for the binary mixture of R744 (carbon dioxide) + R1234yf (2,3,3,3-tetrafluoropro-1-ene) mixture were measured using a metal-bellows variable volumeter. The critical point was determined by visually observing the critical opalescence and reappearance of the meniscus. The expanded combined uncertainties of the critical temperature, critical pressure, critical density, and composition measurements were assessed to be less than 50 mK, 21 kPa, 0.006, and 0.015 (k = 2, 0.95 level of confidence), respectively. The experimental critical properties for the mixture correlated by Redlich-Kister equations were 0.15 % for critical temperature, 0.46 % for critical pressure, 0.10 % for critical density, and 0.08 % for critical molar volume. The mixture formed by mixing about 0.15 M fraction of R1234yf can increase the critical temperature by about 20 K and reduce the critical pressure by about 0.4 MPa compared with the pure material of CO₂.