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Heat and mass transport coefficients in nanopore by molecular dynamics


R. Hannaoui1, G. Galliero1 and C. Boned1

1Laboratoire des Fluides Complexes et leurs Réservoirs (UMR 5150 CNRS/TOTAL), Université de Pau et des Pays de l’Adour, PAU Cedex, France

Keywords: nanopore, molecular dynamics
property: thermodiffusion, thermal conductivity
material: methane

In this work has been studied some thermophysical properties corresponding to the coupled heat and mass transport of fluid binary mixtures confined in slit pore of nanometer size (nanopores). These properties, thermodiffusion (Soret effect), mutual diffusion and thermal conductivity have been quantified by molecular dynamics simulations to evaluate a possible impact of the strong inhomogeneity of the fluid on the effective property as already noticed on viscosity and self-diffusion [1-2].

To perform that study, we used a boundary driven Non-Equilibrium Molecular Dynamics on simple Lennard-Jones mixtures confined in slit pore (atomistic walls) of different pore widths (5 to 35 times the size of a molecule). To compare adequately results for varying pore widths (and with the bulk values) an original Grand Canonical Molecular Dynamics has been developed. Different cases have been analyzed by varying the thermodynamic state, from moderately dense (critical density) to dense situations (liquid like), and the amplitude of the fluid-wall interaction (i.e. the adsorption strength) up to two times the fluid-fluid interaction. To simplify the analysis concerning thermodiffusion, isotope like binary mixtures have been chosen. In such mixtures, the two components are completely equivalent in terms of thermodynamic and adsorption properties which allows to focus on the influence on thermodiffusion of the porous medium alone (confinement + molecular packing in nano-pores) [3].

It has been found that, generally, for pore width above ten times the size of a molecule the confinement and adsorption effects were limited on all effective transport properties simulated (mass diffusion, thermodiffusion and thermal conductivity). However for smaller pore width non negligible deviations compared to the bulk values have been noticed which are probably related to non-local effects.

References
  1. E. Akhmatskaya, B.D. Todd, P.J. Daivis, D.J. Evans, K.E. Gubbins, L.A. Pozhar, Journal of Chemical Physics 106, 4684 (1997).

  2. G. Goel, W.P. Krekelberg, M.J. Pond, J. Mittal, V.K. Shen, J.R. Errington, T. Truskett, Journal of Statistical Mechanics: Theory and Experiment 4, P04006 (2009).

  3. G. Galliero, J. Colombani, P.A. Bopp, B. Duguay, J.P. Caltagirone and F. Montel, Physica A 361, 494 (2006)

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