Acoustic determination of thermophysical properties and critical parameters for the mixture (51 wt % R143a + 49 wt % R125) and critical line of xCO ₂ + (1 - X)(51 wt % R143a + 49 wt % R125)

The thermophysical properties and critical parameters for the alternative refrigerant (51 wt % of 1,1,1 -trifluoroethane (R143a) + 49 wt % of pentafluoroethane (R125))-very close to the composition of R507 (50 wt % of each mixture component)-were investigated using two different acoustic techniques. The critical behavior of the system xCO₂ + (1 - x)(51 wt % R143a + 49 wt % R125) was also investigated. Experimental data of speed of sound in liquid (51 wt % R143a + 49 wt % R125) from T= (253 to 338) K and pressures up to 65 MPa were measured using a pulse-echo method. Derived thermodynamic properties were calculated, combining our experimental data with density and isobaric heat capacity values published by other authors. Measurements of the critical temperature T_c and pressure p_con (51 wt % R143a + 49 wt % R125) and mixtures of xCO₂ + (1 - x)(51 wt % R143a + 49 wt % R125) were performed using another simple ultrasonic time-delay technique. The binary critical line was determined over the whole composition range showing that this system deviates only slightly from ideality since the critical line is a continuous line. The Peng-Robinson equation of state with conventional mixing and combining parameters was used to correlate the binary experimental data.