Molecular dynamics simulations of momentum and thermal diffusion properties of near-critical argon along isobars

• Transport properties of argon were studied near its critical point.
• Equilibrium molecular dynamics simulations showed the critical divergences.
• Shear viscosity and thermal conductivity were in good agreement with NIST data.
• Bulk viscosity can be larger than shear viscosity in the near critical region.
• The Stokes hypothesis is not valid in the near critical region.

Three basic diffusion properties of argon – shear viscosity, bulk viscosity and thermal conductivity – were studied in the neighborhood of the critical point using molecular dynamics (MD) and the Lennard-Jones potential energy function. MD simulations were performed along the 1.0Pc and 1.2Pc isobars. Green-Kubo relations and a Lennard-Jones pair potential were used. Four different sets of Lennard-Jones parameters were used. A comparison of computed shear viscosity and thermal conductivity values with data available from the National Institute of Standards and Technology (NIST) displayed a good agreement. Results for bulk viscosity indicated that values of this property cannot be neglected in this thermodynamic region, a result that violates the traditional and much-assumed Stokes hypothesis in classical fluid mechanics. Furthermore, it was shown that in the neighborhood of the critical region the bulk viscosity can have larger values than the shear viscosity.

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