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Poster De Conférence Année : 2011

Thermodynamic and Transport properties of fluids: towards a single LJ-SAFT like molecular model valid for n-alkanes ?

Résumé

Apart from the low density conditions, there is still a lack of a molecular based approach able to provide both equilibrium and transport properties using the same molecular parameters in all fluid regimes (gas, liquid and supercritical). This is even more critical when dealing with poly-atomic fluids. This lack is largely due to the fact that a comprehensive theory is still not available for evaluating the transport properties in dense fluids in terms of a realistic molecular model, i.e. molecular structure and interaction potentials. However, from the equilibrium properties side, the combination of the Lennard-Jones Chain (LJC) molecular model with the Statistical Associating Fluid Theory (SAFT) is able to represent very well the thermodynamic properties of a great variety of fluids [1]. Furthermore, combined with Density Functional or Density Gradient Theory, these approaches are capable to yield very good results on interfacial properties for the same systems [2]. Additionally, based on Molecular Dynamics simulations results, has been proposed recently semi-empirical accurate correlation to describe viscosity [3] and thermal conductivity [4] of the LJC fluid model over a wide range of thermodynamic states. So, in this work, we have used the LJC molecular model combined with LJ-SAFT and transport properties correlation on normal alkanes (methane, n-butane, n-heptane and n-decane) along the vapour/liquid coexistence line. The idea was to test if, with a single set of molecular parameters for each n-alkane, this model was able to provide a reasonable estimate of both thermodynamic and transport properties. Good results have been obtained for methane (monomer) and n-butane (dimer) except for thermal conductivity in the gas state. For n-heptane (trimer) and n-decane (quadrimer) it has been found that both viscosity and thermal conductivity are not always well estimated using this approach. It will be shown that these trends are fully related to the bad modelling of the internal degrees of freedom when using the LJC model. Furthermore using molecular dynamics simulation it will be shown that, for viscosity, a single additional "rigidity" parameter allows to strongly improve all the results. [1] S. P. Tan, H. Adidharma, M. Radosz, Ind. Eng. Chem. Res., 47 (2008), 8063-8082. [2] P. Paricaud, A. Galindo, G. Jackson, Fluid Phase Equilib 194-197 (2002), 87-96. [3] G. Galliero, C. Boned, Phys. Rev. E, 79 (2009) 021201. [4] G. Galliero, C. Boned, Phys. Rev. E, 80 (2009) 061202.
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hal-00869473 , version 1 (08-07-2019)

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  • HAL Id : hal-00869473 , version 1

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Guillaume Galliero, Christian Boned, Stephanie Delage Santacreu, Marc Odunlami, François Montel. Thermodynamic and Transport properties of fluids: towards a single LJ-SAFT like molecular model valid for n-alkanes ?. SAFT2011, Oct 2011, Pau, France. 2011. ⟨hal-00869473⟩
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