Speed of Sound Measurements and Correlation of {x 3,3,3-Trifluoropropene (HFO-1243zf) + (1−x)2,3,3,3-tetrafluoropropene (HFO-1234yf)} with x = (0.2856, 0.5054, 0.8418) at Temperatures from 243.15 K to 348.15 K and Pressures up to 90 MPa

In the search for a fourth generation of environmentally friendly refrigerants to meet the numerous requirements of the EU F-Gas Regulation (Regulation (EU) No. 517/2014) (European Parliament and Council of the European Union) and the Kigali Amendment to the Montreal Protocol (The Kigali Amendment to the Montreal Protocol: HFC Phase-Down), hydrofluoroolefins (HFOs) have attracted increasing interest in the HVAC&R industry. These compounds are viewed as promising alternatives to the established hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), which are currently being phased out. Despite their potential in terms of thermodynamic and regulatory requirements, a paucity of data has been found in the literature on the thermodynamic properties of HFOs and their mixtures, which are required for the development of dedicated equations of state (EoS). In the present study, the speed of sound of the binary mixture {xR1243zf + (1-x)R1234yf} was measured with a double-path pulse-echo device, previously calibrated through comparison with the IAPWS-95 EOS for water by Wagner and Pru ss (J Phys Chem Ref Data 31: 387, 2002). Measurements were made for three mixtures with x = (0.2856, 0.5054, 0.8418) along 8 isotherms ranging from 243.15 K to 348.15 K and at pressures from near saturation to 90 MPa. The presented data, which to date represent the only available dataset for the speed of sound of the selected mixture, were used to re-tune the binary interaction parameters of a Helmholtz free energy EoS which was previously optimized solely on the basis of experimental VLE data by Fedele et al. (Int J Thermophys 44: 83, 2023). The findings underscore the significance of employing accurate equations of state for each pure fluid composing the mixture. These equations should be founded on comprehensive experimental datasets that incorporate dependable information pertaining to the speed of sound in the liquid phase. The impact of utilizing an inadequate dataset for speed of sound is demonstrated to negatively influence the reliability of the Helmholtz equation of state for the mixture, even following the re-tuning of its binary interaction parameters.