Evaluation of the influence of aggregation morphology on thermal conductivity of nanofluid by a new MPCD-MD hybrid method

Abstract

It is known the thermal conductivity can be elevated considerably by adding nanoparticles in base fluid. But the mechanisms remain unclear so far. One of the most important mechanisms to elevate the thermal conductivity is aggregation of nanoparticles. Molecular dynamics (MD) simulation can be normally employed to model the aggregation behavior in very small system due to the great computational workload. In present work, a new hybrid method of multi-particle collision dynamics and molecular dynamics (MPCD-MD) is proposed to evaluate the morphology of aggregation and thermal conductivity of Cu-H2O nanofluid for reducing the computational workload. Such a hybrid method is very competent for simulating the aggregation process and aggregation morphology of colloidal systems containing more nanoparticles, because the interactions between nanoparticles can be included in MD considering both van der Waals attraction and electrostatic repulsion. In the meanwhile, the hydrodynamic interactions of nanoparticles can be also included easily by the collision step of MPCD. Numerical simulations for various volume fractions and particle sizes at various temperatures are conducted by MPCD-MD, and the fractal dimension and thermal conductivity of Cu-H2O nanofluid are calculated. The numerical results indicate the nanofluid has greater thermal conductivity at lower fractal dimension at fixed volume fraction. The linear relationship between fractal dimension and thermal conductivity is more consistent with the published results in larger colloidal system. This is helpful for us to understand the influence of aggregation morphology of nanoparticles on the thermal conductivity of nanofluid.