Interfacial properties of fluorinated (F)-gases in azeotropic condition

Abstract

The interfacial behavior in refrigerant mixtures has a major impact on heat transfer coefficients during the vaporization and condensation stages. Therefore it is appropriate to have robust models to predict their properties. In this work, molecular dynamic simulations together with density gradient theory combined with the statistical associating fluid theory of variable range employing a Mie potential (SAFT-VR-Mie) have been employed to model and understand the interfacial behavior in systems of azeotropic refrigerant mixtures of fluorinated gases (R32, R125, R134a, R143a, and R152a) blended with propane (R290). It is demonstrated that despite the high-non ideal behavior in these mixtures, both approaches are capable of reproducing the minimum in surface tension (aneotropy) as a function of composition and temperature for the considered mixtures. It is concluded that the minimum occurs close but not equal to the azeotropic condition. Besides, it is also observed that the azeotropic condition acts as a switching point, in which R290 starts to accumulate at the interface positively. In contrast, in all mixtures, mixtures F-gases do not exhibit surface activity. Finally, the involving azeotropic condition was reduced, without loss of rigor, to a simpler problem that involves the VLE of a pseudo-pure component, in which molecular properties are characterized to be used in molecular simulations.