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Estimation of thermodiffusion in ternary alkane mixtures using molecular dynamics simulations and an irreversible thermodynamic theory
Guillaume Galliero, Seshasai Srinivasan and M. Ziad Saghir

Thermal diffusion ratios of three components hydrocarbon mixtures have been computed using molecular dynamics (MD) simulations on model fluids and a theory based on the thermodynamic of irreversible process (IRT). Six different mixtures of methane, n-butane and n-dodecane at T = 333.15 K and P = 35 MPa were investigated. For the MD approach the Lennard-Jones (LJ) as well as the Lennard-Jones chain (LJC) fluid models were employed. Further, for each of these two fluid models three different combination rules were applied, viz., Lorentz-Berthelot (LB), Kong (KG) and Waldmann-Hagler (WH). In the IRT approach, estimation of thermal diffusion was made using the Firoozabadi’s theory coupled with the translated Peng-Robinson (PR) equation of state. In all cases and for all approaches, methane and n-butane exhibit a migration towards the hot areas whereas n-dodecane migrates towards the cold areas. The results from the MD theory using LJC model and LJ model combined with the LB combining rules, and the IRT principles using PR equation of state had a close agreement for the mixtures studied in this work.

Keywords: Thermodiffusion, Soret effect, Molecular Dynamics, Irreversible Thermodynamic, Alkane, Lennard-Jones, Lennard-Jones chain, Combining rules, Ternary mixtures.

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