Anomalous enhancement in thermal conductivity of nanofluid induced by solid walls in a nanochannel

Thermal conductivity of Ar–Cu nanofluid confined between two parallel walls (in a nanochannel) is calculated by equilibrium-molecular-dynamics (EMD) simulation through Green-Kubo formula. The results show that the vibration of nanoparticle in the channel height direction (z-direction) is inhibited due to the presence of solid boundaries and accordingly the thermal conductivity of the confined nanofluid is obviously anisotropic. Anomalous enhancement in the thermal conductivity perpendicular to the z-direction (λ∗) appears as a result of the strong coupling interactions between the fluid atoms, especially the nanoparticle atoms, and the wall atoms. The thermal conductivity λ∗ of the nanofluid confined in the channel of width h = 5.148 nm increases with the increase of the nanoparticle diameter for the strengthened couplings. The nanoparticle volume fraction effect on the thermal conductivity of the confined nanofluid is more obvious than that in macroscale. In addition, the thermal conductivity λ∗ of the nanofluid with diameter of nanoparticle d = 1.370 nm decreases with the channel width increasing owing to the weakened couplings resulted by a longer interacting distance.