Simultaneous determination of thermal conductivity and shear viscosity using two-gradient non-equilibrium molecular dynamics simulations

ABSTRACT

A method for the simultaneous determination of the thermal conductivity λ and the shear viscosity η of fluids by non-equilibrium molecular dynamics simulations is presented and tested using the Lennard-Jones truncated and shifted fluid as example. The fluid is studied under the simultaneous influence of a temperature gradient and a velocity gradient and the resulting heat flux and momentum flux are measured to determine λ and η. The influence of the magnitude of and on λ and η is investigated. The cross-effects are negligible, even for large gradients. The same holds for the influence of on λ. However, there is a significant influence of on η, i.e. shear-thinning. The two-gradient method is applied in different ways: for small temperature-averaged values of λ and η are obtained. As has no significant influence on the results, simulations with large are evaluated using the local-equilibrium assumption, such that values are obtained at different temperatures in a single simulation. In addition to the results for λ and η, also results for the self-diffusion coefficient D are determined from evaluating the mean squared displacement. The new two-gradient method is robust, efficient and yields accurate results.

GRAPHICAL ABSTRACT

KEYWORDS:

• Thermal conductivity
• shear viscosity
• self-diffusion coefficient
• Lennard-Jones
• shear-thinning

Acknowledgments

The present research was conducted under the auspices of the Boltzmann-Zuse Society for Computational Molecular Engineering (BZS).

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Martin P. Lautenschlaeger http://orcid.org/0000-0003-3266-4218

Additional information

Funding

The authors gratefully acknowledge financial support by the DFG within IRTG 2057 Physical Modeling for Virtual Manufacturing Systems and Processes. The simulations were carried out on the elwe at Regional University Computing Center Kaiserslautern (RHRK) under the grant TUKL-TLMV as well as on the SuperMuc at Leibniz Supercomputing Centre (LRZ) Garching under the grant SPARLAMPE (pr48te).