Experimental speed of sound in two emerging mixture working fluids of [R1234ze(Z) + R1233zd(E)] and [R1234ze(Z) + isobutane]

There is a continuous demand for accurate data on the thermodynamic properties of environmentally friendly working fluids, specifically hydrofluoroalkenes (HFO) and hydrocarbons (HC). For two emerging binary mixture fluids in organic Rankine cycle and heat pump, [R1234ze(Z) (or named cis-1,3,3,3-tetrafluoropropene) + R1233zd(E) (or named trans-1-chloro-3,3,3-trifluoro-1-propene)] and [R1234ze(Z) + isobutane], the speed of sound was experimentally obtained at pressure between 40 and 960 kPa and temperature interval of 300 to 370  K. The experimental instruments of the fixed-path acoustic resonance method have been re-calibrated and repaired to confirm the experimental precision, and the relative combined expanded uncertainty (k = 2) of the speed of sound is less than 0.038 %. Due to the signal peak overlapping in gas chromatography, the molar fractions are instead calculated by the experimental data using the thermodynamic rules, with the absolute combined expanded uncertainty (k = 2) of 0.0027 and 0.0008 for R1234ze(Z) + R1233zd(E) and R1234ze(Z) + isobutane, respectively. Acoustic virial coefficients were derived according to the truncated acoustic virial equation using the experimental data of this and previous work. The obtained data were compared with themselves to confirm the basic reliability. The experimental data were also compared with the reference values calculated by the state of art of thermodynamic models and a maximum deviation was found up to 20 times the experimental uncertainty, proposing needs and references for new dedicated mixing models.