Fundamental Equations of State for <i>cis</i>-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 pρT and derived properties over wider ranges of temperature and pressure. This equation is given in the Appendix.