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In this work, the equilibrium molecular dynamics (MD) simulation combined with the Green–Kubo method is employed to calculate the thermal conductivity and investigate the impact of the liquid layer around the solid nanoparticle (NP) in enhancing thermal conductivity of nanofluid (argon–copper), which contains the liquid argon as a base fluid surrounding the spherical or cylindrical NPs of copper. First, the thermal conductivity is calculated at temperatures 85, 85.5, 86, and 86.5 K and for different volume fractions ranging from 4.33% to 11.35%. Second, the number ΔN of argon atoms is counted in the liquid layer formed at the solid–liquid interface with the thickness of Δr = 0.3 nm around the NP. Finally, the number density n of argon atoms in this layer formed is calculated in all cases. Also, the results for spherical and cylindrical NPs are compared with one another. It is observed that the thermal conductivity of the nanofluid increased with the increasing volume fraction and the number ΔN. Likewise, the thermal conductivity of nanofluid containing spherical NPs is higher than that of nanofluid containing cylindrical NPs. Furthermore, the number density n of argon atoms near the surface of spherical NPs is higher than that of argon atoms attached in the curved surface of cylindrical NPs. As a result, the liquid layer around the solid NP has been considered one of the mechanisms responsible contributing to the thermal conductivity enhancement in nanofluids.

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In this work, The Equilibrium Molecular Dynamics (EMD) is applied for computing the thermal conductivity of aqueous nanofluids containing graphene nanosheets (aqueous GNFs), through Green-Kubo framework and studying the effects of concentration and temperature on thermal conductivity enhancement of aqueous GNFs. The SPC/E water model was chosen and the interactions for water molecules have been modelled by the Lennard-Jones (L-J) potential combined with Coulomb potential, as well as a simple body (L-J) potential is used to model the interactions between graphene atoms. The numerical calculations of thermal conductivity are performed in the temperature range of 293-343K and for graphene nanosheets volume fraction 0.175%, 0.190%, 0.306%, 0.521% and 0.722%. Firstly, the molecular dynamics code and the Green-Kubo framework are validated by comparing the thermal conductivity with the previous experimental studies. The results have showed that the thermal conductivity enhancement increases with increasing volume concentration and is substantial even at lower concentrations. However, this enhancement has been not predicted by the classical Maxwell's model. Furthermore, the enhancement depends on temperature, especially, the thermal conductivity of aqueous nanofluids containing graphene nanosheets (aqueous GNFs) increases with increasing system temperature.