A Procedure for Calculating the Surface Tension at the Water to Steam-and-Fluorocarbon Gas Interface
Abstract
The article presents a procedure for calculating the surface tension at the water to a steam-and-fluorocarbon gas mixture interface. The proposed procedure is based on the previously published analytical methods for calculating the surface tension for simple one-component liquid–vapor systems. A problem concerned with intermolecular interaction between the surface molecules of liquid and vapor of the same physical nature and the molecules of surfactants is considered. The obtained analytical correlation for calculating the surface tension at the interface between water and a mixture of water and fluorocarbon vapors is a function of temperature and concentration of fluorocarbon gas in the mixture, which remains valid for molecules of any size. A method for determining the mutual orientation of the liquid and surfactant molecules near the interface is proposed proceeding from the principles of the minimum potential energy at the interface and of the maximum intermolecular interaction for substances of different physical nature, and after calculating the number of the degrees of freedom for the molecules of mixture components. A software module for calculating the surface tension on the phase interface boundary has been developed. The predicted calculated values of surface tension at the interface between water and a steam-and-fluorocarbon gas mixture are obtained. It has been found from a numerical analysis that the orientation of molecules in the surface layer of water and in a monomolecular layer of the mixture can significantly alter the mixture surface tension in the entire range of studied temperatures and concentrations of surfactants. Thus, symmetrical molecules of SF6 gas have little effect on the mixture surface tension, whereas the long molecules of C3F8 and C4F10 are oriented perpendicular to the interface surface, causing the surface tension to change by several times. A numerical experiment has shown that this phenomenon is also due to significant adsorption of the C3F8 and C4F10 molecules at the interface surface. For example, with the C3F8 volume concentration equal to 0.05 away from the interface, the C3F8 volume concentration equal to about 0.4 takes place at the interface surface. The authors point out that the developed calculation procedure requires verification, and the calculation results are preliminary in nature and should be put in consistency with the available and new experimental data.
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Для цитирования: Ежов Е.В., Охотин В.С., Тарасов П.В., Кузнецов В.Н. Методика расчета поверхностного натяжения на границе раздела фаз вода – смесь водяного пара и фторуглеродного газа // Вестник МЭИ. 2017. № 5. С. 40—47. DOI: 10.24160/1993-6982-2017-5-40-47.
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For citation: Ezhov E.V., Okhotin V.S., Tarasov P.V., Kuznetsov V.N. A Procedure for Calculating the Surface Tension at the Water to Steam-and-Fluorocarbon Gas Interface. MPEI Vestnik. 2017; 5:40—47. (in Russian). DOI: 10.24160/1993-6982-2017-5-40-47.
