A Helmholtz Energy Equation of State for Calculations of Thermodynamic Properties of trans-1,2-Difluoroethene [R-1132(E)]

Abstract This work presents a fundamental equation of state for calculations of the thermodynamic properties of R-1132(E), which is a potential refrigerant for residential or mobile air conditioners. The equation of state has a functional form expressed explicitly in the Helmholtz energy with temperature and density as the independent variables, and the form is fitted to consistent experimental datasets, including the critical parameters, vapor pressure, saturated liquid and vapor densities, $$(p, \rho , T)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>(</mml:mo> <mml:mi>p</mml:mi> <mml:mo>,</mml:mo> <mml:mi>ρ</mml:mi> <mml:mo>,</mml:mo> <mml:mi>T</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> behavior, vapor-phase sound speed, and ideal gas isobaric heat capacity. The equation of state is valid between temperatures from 240 K and 400 K, with pressures up to 6.5 MPa. In this range, expected relative uncertainties at the 95 % confidence interval ( $$k=2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>k</mml:mi> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> ) are 0.1 % for liquid densities, 0.4 % for vapor densities, and 0.1 % for vapor-phase sound speeds, except at the saturation states and in the critical region where larger deviations of up to 2 % are possible in densities due to higher experimental uncertainties. The uncertainty in calculated vapor pressures is 0.15 % above 275 K, which is larger at lower temperatures due to their small values. Various plots of derived properties from the equation of state show that the equation exhibits qualitatively correct behavior over wide ranges of temperature and pressure.