Fundamental Equations of State for cis-1,3,3,3-Tetrafluoropropene [R-1234ze(Z)] and 3,3,3-Trifluoropropene (R-1243zf)

New fundamental equations of state are presented for cis-1,3,3,3-tetrafluoropropene [R-1234ze(Z)] and 3,3,3-trifluoropropene (R-1243zf). The new equation for R-1234ze(Z), which is the main topic of this paper, is applicable to ranges at lower temperatures and higher pressures compared to the first published equation, and uncertainties in liquid-phase sound speeds are greatly improved. The equation is valid at temperatures from 238 to 440 K at pressures up to 34 MPa. Estimated uncertainties in this range are 0.1% for vapor pressures at temperatures above 300 K and 0.3% at lower temperatures, 0.1% for liquid-phase densities, 0.3% for vapor-phase densities, 0.02% for vapor-phase sound speeds, and 0.05% for liquid-phase sound speeds, except in the critical region where larger deviations up to about 1% are observed in density. The equation shows reasonable extrapolation behavior at extremely low and high temperatures, and at high pressures. The new equation for R-1243zf has a similar range of validity and uncertainties as with the first published equation, but it is designed to exhibit better behavior for p rho T and derived properties over wider ranges of temperature and pressure. This equation is given in the Appendix.