Modification of the Redlich-Kwong-Aungier Equation of State to Determine the Main Thermodynamic Parameters in the Pure Liquid CO2 Region

Abstract

The most important parameters for determining the state of real gas and the thermodynamic properties of the working fluid in a pure liquid region are pressure, specific volume, enthalpy and entropy. The paper presents a modified Redlich-Kwong-Aungier equation of state for determining pressure, specific volume, enthalpy and entropy in the pure liquid phase of real gas. CO2 was selected as the studied working fluid. When solving this problem, the author identified the main parameters of liquid carbon dioxide thermo-dynamics with the least error in comparison with experimental data in a wide range from 220 K to 300 K. It is possible to calculate pressure, specific volume, density, enthalpy and entropy of liquid CO2 with the help of the proposed method, for which the initial data are temperature, density, critical properties, molar mass and acentric factor of the working fluid. In particular, a modified Redlich-Kwong-Aungier equation is used to calculate the pressure of the working fluid. The author proposes a correlation equation of the scale correction, which is used in the Redlich-Kwong-Aungier equation for CO2 in the region of pure liquid phase. The results obtained for the pressure, enthalpy and entropy of liquid CO2 showed good agreement with the basic values, which provides the application of the proposed method in the field of pure liquid CO2, limited by the temperature range from 220 K to 300 K. The simplicity of the equation of state and the small number of empirical coefficients allows to use this method to solve practical problems of computational gas dynamics without spending a lot of time on calculations.