Molecular dynamics simulation of nanofluid's effective thermal conductivity in high-shear-rate Couette flow

Effective thermal conductivity of Ar-Cu nanofluid in shear field is calculated by equilibrium molecular dynamics (EMD) simulation using Green-Kubo formula. The shear field is formed by imposing constant shear rate Couette flow with modified Lees-Edwards periodic boundary condition. The nanoparticle in the nanofluid in shear field rotates under the action of the velocity gradient. The rotation induces enhanced "microconvection" effect which is the main reason for the linear increase in the effective thermal conductivity of the shearing nanofluid with the shear rate increasing. The increase is more sharply with lower volume fraction of nanoparticle than with higher volume fraction, because the "microconvection" effect is weakened in the nanofluid with higher volume fraction of nanoparticle resulted by the slower nanoparticle rotation speed. The effective thermal conductivity obtained from the conventional correlation which is proposed for the flowing suspensions containing micro-sized particles are significantly lower than our numerical results. Moreover, the effect of nanoparticle volume fraction is more obvious in our numerical results. Therefore, the conventional correlation is not suitable when the sizes of the suspended particles are reduced to nanometers (nanofluid).