Thermodynamic properties of perfluorooctane on the liquid-gas coexistence curve: calculation method and tabulated data
Authors: Rykov S. V. , Popov P. V. , Kudryavtseva I. V. , Rykov V. A. 
Published: September 2024

A technique has been developed for constructing a phase equilibrium line in the range from the triple to the critical point for a technically important substance, perfluorooctane (C8F18), which is currently used in various fields of industry and medicine. The proposed phase equilibrium line model includes the following equations: vapour pressure; saturated liquid density; saturated vapour density; “apparent” heat of vaporization. In this case, the vapour pressure equation satisfies the requirements of the scale theory of critical phenomena near the critical point, and the Wegner model in the vicinity of the triple point. The coexistence curve model in the vicinity of the critical point satisfies the Yang-Yang model and renormalization group theory for asymmetric systems, and in the region of rarefied gas it satisfies the linear model of average diameter. In the temperature range 246.15–496.99 K, table for perfluorooctane have been developed, including pressure and density of saturated vapor, density of saturated liquid, heat of vaporization, first and second derivatives of saturated vapor pressure. Using latest experimental data, as well as experimental data on the critical pressures of perfluoroalkanes as a function of their molecular weight, the following values of critical parameters were selected: critical pressure – 1.548 MPa, critical density – 596.4 kg/m3, critical temperature – 496.99 K. A number of statistical characteristics were calculated, including absolute mean deviation and standard deviation, characterizing the accuracy of the proposed phase equilibrium line model when describing experimental data obtained in generally recognized international thermophysical laboratories. The results obtained are useful for high-tech companies engaged in the development of innovative technologies: in the field of radio-electronic and electrical industries, in which perfluorooctane is used as a liquid dielectric and coolant; in medicine, where perfluorooctane is used as a gas transport liquid and is used for ophthalmic purposes; magnetic fluid sealers for the purpose of isolating hazardous substances from the environment and seals for devices operated in vacuum conditions or in contact with aggressive substances; magnetic fluid separators for separating non-ferrous metals by density, etc. The results of this study can also be used in developing the fundamental equation of state for perfluorooctane. The results obtained are useful for high-tech companies engaged in the development of innovative technologies: in the field of radio-electronic and electrical industries, in which perfluorooctane is used as a liquid dielectric and coolant; in medicine, where perfluorooctane is used as a gas transport liquid and is used for ophthalmic purposes; magnetic fluid sealers for the purpose of isolating hazardous substances from the environment and seals for devices operated in vacuum conditions or in contact with aggressive substances; magnetic fluid separators for separating non-ferrous metals by density, etc. The results of this study may also be useful in developing the fundamental equation of state for perfluorooctane.