Molecular Dynamics Simulation Of Nanofluids Transport Phenomenon

The transport phenomenon of nanofluids is studied using molecular dynamicssimulation in this work. Nanofluids are solid-liquid composite materials consisting ofsolid nanoparticles or nanofibers, with size typically on the order of1-50nm,suspended in the liquids. Compared with the conventional suspension, nanofluids havea anomalously high thermal conductivity at low nanoparticle concentrations and thisattracted people’s great interest. Despite the research of the heat conductionmechanism of nanofluids has developed rapidly in the past ten years, it is still a field inits adolescence, and there are a number of issues which have not been fullyinvestigated.Mechanism of heat conduction in copper-argon nanofluids is studied by moleculardynamics simulation and the thermal conductivity was obtained using the Green-Kubomethod. While the interatomic potential between argon atoms are described using thewell-known Lennard-Jones (L-J) potential, a more accurate embedded atom method(EAM) potential is used in describing the interatomic interaction between copperatoms. It is found that the heat current autocorrelation function obtained using L-Jpotential to describe the copper-copper interatomic interaction fluctuates periodicallydue to periodic oscillation of the instantaneous microscopic heat fluxes. Thermalconductivities of nanofluids using EAM potentials were calculated with differentvolume fractions but the same nanoparticle size. The results show that thermalconductivity of nanofluids is almost linear function of the volume fraction and slightlyhigher than the results predicted by the conventional effective media theory for welldispersed solution. A solid-like base fluid liquid layer with thickness of0.6nm wasfound in the simulation and this layer is believed to account for the small discrepancybetween the results of MD simulation and the conventional effective media theory.Effect of nanoparticle aggregation on the thermal conductivity and viscosity ofnanofluids is also studied by molecular dynamics simulation in this work. Thermalconductivity and viscosity of the nanofluid are calculated using Green-Kubo methodand results show that the nanoparticle aggregation induces a significant enhancementof thermal conductivity in nanofluid, while the increase of viscosity is moderate. Theresults also indicate that different configurations of the nanoparticle cluster result indifferent enhancements of thermal conductivity and increase of viscosity in thenanofluid. The differences between equilibrium molecular dynamics (EMD) approach and non-equilibrium molecular dynamics (NEMD) approach in obtaining thethermo-physical properties of nanofluids are also discussed.The non-equilibrium phenomenon of nanofluids is also studied in this work. It isfound that the coupling factor goes large when the volume fraction of the nanoparticleincreases, while it goes small when the diameter of the nanoparticle increases. What’smore, in the temperature range of90K-110K, the temperature has no effect on thecoupling factor. In addition, when there is nanoparticle aggregation in the nanofluidssystem, the coupling factor goes small.This work is supported by National Science Foundation of China (No.51076105,No.50876067, No.50828601), Board of the Development Fund projects in Shanghai(No.10ZZ91), Shanghai Academic discipline project (No. J50501).