A Fundamental Equation of State for Ethanol

TLDR: In this paper, a new fundamental equation for ethanol, in the form of Helmholtz energy as a function of temperature and density, is presented, along with ancillary equations for vapor pressure, saturated liquid density, saturated vapor density, and ideal gas heat capacity.

Abstract: The existing fundamental equation for ethanol demonstrates undesirable behavior in several areas and especially in the critical region. In addition, new experimental data have become available in the open literature since the publication of the current correlation. The development of a new fundamental equation for ethanol, in the form of Helmholtz energy as a function of temperature and density, is presented. New, nonlinear fitting techniques, along with the new experimental data, are shown to improve the behavior of the fundamental equation. Ancillary equations are developed, including equations for vapor pressure, saturated liquid density, saturated vapor density, and ideal gas heat capacity. Both the fundamental and ancillary equations are compared to experimental data. The fundamental equation can compute densities to within ±0.2%, heat capacities to within ±1%–2%, and speed of sound to within ±1%. Values of the vapor pressure and saturated vapor densities are represented to within ±1% at temperatures of 300 K and above, while saturated liquid densities are represented to within ±0.3% at temperatures of 200 K and above. The uncertainty of all properties is higher in the critical region and near the triple point. The equation is valid for pressures up to 280 MPa and temperatures from 160 to 650 K.