The Vapor–Liquid Phase Equilibrium Line for Water within the Framework of the Renormalization Group Theory

The article proposes an equation system that includes functions describing the properties of H₂O at the saturation line (pressure, vapor density, liquid density, saturated vapor pressure derivative, heat of vaporization, etc.). Firstly, this system satisfies the requirements of the renormalization group theory. Secondly, the system is in consistency with the Yang–Yang hypothesis in the critical point neighborhood. For describing the saturated vapor density, the Clausius–Clapeyron equation is involved. In writing the equation system, complexes characterizing the saturation line mean diameter behavior were used. The equation system includes: a) the complexes, which are selected in accordance with the recommendations suggested by Wang et al. for asymmetrical systems, b) critical indices, which are calculated on the basis of the critical point scale theory methods. Using the equation system, numerical values of the water property indicators are obtained in the range from the triple point temperature to the critical temperature. The uncertainty of the above-mentioned values are in satisfactory agreement with the uncertainties: a) of the corresponding data on the properties calculated by Wagner and Pruss in the range from the triple point temperature to the critical temperature, b) of the known experimental data. Various models of the saturation line and elasticity curve are compared with each other. It is shown that the proposed equation system conveys the available experimental information on the equilibrium water properties with a smaller uncertainty than the known models do. Data on the mean diameter are calculated on the basis of the equation system in a wide interval of relative temperatures, including the critical point neighborhood. It is discussed a behavior of this diameter within the framework of some known models.