FUNDAMENTAL EQUATIONS OF STATE WITH AN IDENTICAL FUNCTIONAL FORM FOR HFO-1234yf AND HFO-1234ze(E)

New fundamental equations of state explicit in the Helmholtz energy are presented for 2,3,3,3-tetrafluoropropene (HFO-1234yf) and trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)). The equations have the same functional form for their residual part. All thermodynamic properties can be derived from the equations. The equation for HFO-1234yf covers temperatures between 240 K and 400 K for pressures up to 40 MPa, and that for HFO-1234ze(E) is valid for temperatures from 240 K to 420 K and for pressures up to 15 MPa. The estimated uncertainties of the equations are 0.1 % in liquid density, 0.05 % in the vapor phase speed of sound, and 0.1 % in vapor pressure. Both equations exhibit reasonable behavior in extrapolated region outside the range of the experimental data.