Surface tension of binary mixtures including polar components modeled by the density gradient theory combined with the PC-SAFT equation of state


V. Vinš1, J. Hrubý1 and B. Planková1

1Institute of Thermomechanics AS CR, Prague, Czech Republic

Keywords: density gradient theory, PC-SAFT
property: surface tension
material: polar fluids, carbon dioxide

Interfacial properties of fluids play an important role in many technical processes such as flow through porous media, distillation, nucleation, two-phase mass and heat transfer. However, the surface tension of many mixtures is still described only partly and the experimental data are scarce.

In this study, we use the Cahn-Hilliard density Gradient Theory (GT) [1] for predicting the surface tension of various binary mixtures at relatively wide temperature ranges. The GT was combined with a physically based equation of state (EoS), namely the Perturbed-Chain (PC) Statistical Associating Fluid Theory (SAFT). The GT combined with the PC-SAFT EoS has already been successfully used for example by Fu et al. for predicting the surface tension of non-polar and non-associating binary mixtures containing carbon dioxide or methane [2]. In our study we focus on binary mixtures with polar components. The original PC-SAFT EoS was therefore extended with a polar term in the expression for the residual Helmholtz free energy in the manner proposed by Gross [3]. The Perturbed-Chain Polar (PCP) SAFT EoS provides more accurate results for both the quadrupolar and dipolar substances than the original PC-SAFT EoS.

Besides the planar phase interface used for the surface tension prediction, the GT combined with the PCP-SAFT EoS was applied also on the spherical phase interface [4]. The GT allows solving the critical cluster size occurring during the nucleation of droplets. Application of the PCP-SAFT EoS provides significant improvement compared to classical cubic Peng-Robinson EoS used in the previous study [5].

References
  1. J.W. Cahn, J.E. Hilliard, J. Chem. Phys. 28, 258 (1958)

  2. D. Fu, H. Jiang, B. Wang, S. Fu, Fluid Phase Equilib. 279, 136 (2009)

  3. J. Gross, AIChE J. 51, 2556 (2005)

  4. V. Vinš, J. Hrubý, B. Planková, Experimental Fluid Mechanics 2009, Proceedings of the international conference, November 24-26 2010, Liberec, Czech Rep.

  5. J. Hrubý, D.G. Labetski, M.E.H. van Dongen, J. Chem. Phys. 127, 164720 (2007)

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