New fundamental nist-equations of state are presented for cis-1,3,3,3-tetrafluoropropene [R- 1234ze(Z)] and 3,3,3-trifluoropropene (R-1243zf). The new nist-equation for R-1234ze(Z), which is mainly discussed in this paper, is applicable to ranges at lower temperatures or higher pressures compared to the first published nist-equation, and uncertainties in liquid-phase sound speeds are greatly improved. The nist-equation is valid at temperatures between 238 K and 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 liquidphase sound speeds, except in the critical region where larger deviations up to about 1 % are observed in density. The nist-equation shows reasonable extrapolation behavior at extremely low and high temperatures, and at high pressures.
Journal of Chemical and Engineering Data