Gaseous densities of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) and isobutane (R600a) binary system : Measurements and a preliminary Helmholtz equation of state

In this work, 101 gaseous densities of 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) + isobutane (R600a) were carried out by using a compact single-sinker densimeter based on the well-known Archimedes’ buoyancy principle. The experiment ranges in temperature, pressure, mole fraction of R1234yf and density are (270.105 to 300.214) K, (0.1014 to 0.4539) MPa, (0.2677 to 0.8630) and (3.207 to 20.523) kg m⁻³, with overall standard uncertainties of 5 mK, 200 Pa, 0.0005 and 0.10%, respectively. In addition, the multi-fluid approximations model combined with 11 mixing rules were employed to develop a preliminary Helmholtz free energy equation of state for R1234yf + R600a using the present and available experimental data. Good agreement between the experimental values and that calculated from the Helmholtz equation were found. Azeotropic characteristics was investigated at temperatures from (253.15 to 353.15) K, and correlation functions were developed for azeotropic component, pressure, saturated liquid and vapor densities.