Accuracy of Approximations to the Poynting Correction for Ice and Liquid Water
Allan H. Harvey
Rigorous calculation of the Poynting correction, which describes the effect of pressure on the fugacity of a condensed phase, requires time-consuming evaluation of a thermodynamic potential such as the IAPWS-95 formulation for water. Simplifying approximations are used in many applications, but the error introduced by the approximations is seldom evaluated. In this work, we develop first-order and second-order approximations for the Poynting correction for both ice and liquid water (including supercooled liquid water) and evaluate their errors by comparison to the full thermodynamic potentials. The range of conditions covered is from -100 C to 200 C at pressures to 20 MPa. Some implications for the calculation of the enhancement factor used in humidity metrology are discussed.
Accuracy of Approximations to the Poynting Correction for Ice and Liquid Water, Journal of Research (NIST JRES), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://doi.org/10.6028/jres.122.041
(Accessed February 24, 2024)