Measurement of critical properties for the binary mixture of R744 (carbon dioxide)+R1234ze(E) (trans-1,3,3,3-tetrafluoropropene)

In the context of global warming and demanding alternative refrigerants, the transcritical CO(2 )refrigeration cycle was considered a potentially energy-saving and carbon-reducing technology. The use of CO2 mixtures with higher critical temperatures and lower critical pressures has been demonstrated as an effective way to improve the performance of transcritical CO2 refrigeration cycles. To achieve this approach, accurate critical locus parameters are needed for establishing cross-over state equations and calculating thermodynamic properties in the near-critical region. Currently, experimental methods are the most effective way to obtain high-precision critical locus parameters of mixtures. In this work, the critical properties including critical temperature, critical pressure, critical density, and mole fraction of the R744 (carbon dioxide) + R1234ze(E) (trans-1,3,3,3-tetrafluoropropene) binary mixture were measured according to a variable-volume method with a metal-bellows volumeter. The critical point was determined by visual observation of the critical opalescence and reappearance of the vaporliquid meniscus. The combined expanded measurement (relative) uncertainties of the critical temperature, critical pressure, critical density, and mole fraction were within 50 mK, 0.021 MPa, 0.6%, and 0.012 (k = 2, 0.95 level of confidence), respectively. After comparing the fitting results of the Modified Chueh-Prausnitz (MCP) method, the Modified Wilson (MW) method, and the Redlich-Kister (RK) method. We recommended the Modified Wilson method to correlate the critical properties of the binary system of R1234ze(E)+R744. Our research showed that R1234ze(E)+R744 mixture can achieve a higher critical temperature and critical density simultaneously and a lower critical pressure compared with pure CO2 when the composition of R744 is less than 0.23.