Dielectric Permittivity and Thermophysical Properties of Carbon Dioxide
in Critical Point Region
Onishchenko V.P., Zhelezny V.P., Dzhenkov M.Yu.
Odessa State Academy of Refrigeration
Construction of theoretically proved equations of a condition of gases and liquids is of
interest for the solution of a number of practical technological problems, in particular,
designing the gas extraction processes in overcritical region of parameters.
The thermodynamic perturbation theory allows reaching the prediction of
thermodynamic properties of polar and non-polar gases and liquids within the error, close to
an error of experimental data. Thus was used the Lennard - Jones potential with the
parameters dependent on temperature [1]. The collective phenomena, which start to manifest
in gases of moderate density and grow in liquid, result in screening of intermolecular
interaction potential. These phenomena are fully taken into account within the thermodynamic
perturbation theory for the description of thermal and caloric properties in single-phase
region. However they are not fully taken into account for the description of properties within
near-critical regions of a liquid - vapour equilibrium. Similarly, these collective phenomena
and intermolecular interaction potential screening detetermine dependences of dielectric
permittivity on temperature and density.
This work presents the results of simulation of dependence both of thermodynamic
properties and of dielectric permittivity of carbon dioxide within near-crytical area of state
parameters. Screening parameters enter relations of thermodynamic perturbation theory in the
formulation [1] and on semi-empirical basis they are connected to dielectric permittivity.
Results of detailed comparison to experimental data [2] for carbon dioxide are presented. For
example, the error of the description of pressure on near-critical isotherms does not exceed
0,1 МPа.
1. Onishchenko V.P., Kutirkin O.F., Zhelezny V.P., Vladimirov B.P. Thermodynamic properties of polar
fluids: ozone - safe refrigerants in gaseous and liquid states // High Temperatures - High Pressures, GB. 1997. - Vol. 29. - p. 313 - 318.
2. Span R., Wagner W. A New Equation of State for Carbon Dioxide // J. Phys. Chem. Ref. Data - 1996. Vol.
25, No. 6. - p. - 1520.