A Fundamental Equation of State for 1, 1-Difluoroethene (R-1132a)

A new fundamental equation of state is presented for 1, 1-difluoroethene (R-1132a), which is a promising low-GWP refrigerant for ultra-low-temperature refrigeration. The equation of state is expressed explicitly in terms of the Helmholtz energy with temperature and density as the independent variables. The equation is applicable at temperatures from the triple-point temperature (111.0 K) to 400 K at pressures up to 30 MPa. In this range, the expected expanded uncertainties ( $$k = 2$$ ) in calculated properties are estimated to be 0.3 % for vapor pressures, 0.3 % for liquid densities, 0.5 % for vapor densities, 0.8 % for saturated liquid densities, 2 % for saturated vapor densities, 0.5 % for liquid-phase sound speeds, and 0.2 % for vapor-phase sound speeds. These uncertainties represent a substantial improvement over the preliminary equation of state for this refrigerant. Differences between experimental and calculated vapor pressures are within 5 kPa in most cases. Illustrative plots of derived properties demonstrate that the present equation of state exhibits physically consistent behavior throughout the range of validity and maintains reasonable extrapolation behavior at extremely low and high temperatures, and at high pressures. Supporting files are provided for implementation in REFPROP and TREND.