Thermal Conductivity Computation of Nanofluids by Equilibrium Molecular Dynamics Simulation: Nanoparticle Loading and Te
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1022-II01-08
Thermal Conductivity Computation of Nanofluids by Equilibrium Molecular Dynamics Simulation: Nanoparticle Loading and Temperature Effect Suranjan Sarkar, and R. Panneer Selvam Computational Mechanics Laboratory, University of Arkansas, BELL 4190, University of Arkansas, Fayetteville, AR, 72701
ABSTRACT A model nanofluid system of copper nanoparticles in argon base fluid was successfully modeled by molecular dynamics simulation. The effective thermal conductivity of the nanofluids was calculated through Green Kubo method in equilibrium molecular dynamics simulation for varying nanoparticle concentrations and for varying system temperatures. Thermal conductivity of the basefluid was also calculated for comparison. This study showed that effective thermal conductivity of nanofluids is higher than that of the base fluid and found to increase with increased nanoparticle concentration and system temperature. Through molecular dynamics calculation of mean square displacements for basefluid, nanofluid and its components, we suggested that the increased movement of liquid atoms in the presence of nanoparticle was one of the probable mechanisms for higher thermal conductivity of nanofluids. INTRODUCTION Nanofluids have been shown to have effective thermal conductivities (TC) much higher than that of the basefluids [1-3] with the addition of small volume of nanoparticles or nanotubes. However, the temperature dependence of thermal conductivities has been much less studied so far. Few available studies have shown strong temperature dependent behavior of thermal conductivity of nanofluids [4]. Conventional theories like Hamilton Crosser (HC) theory [5] based on continuum models not only under predicts the relative increase in TC, but also unable to predict the temperature and nanoparticle size dependency of the TC of nanofluid suspensions. This model indicates that TC of nanofluid is merely a function of only its component elementÃs conductivity and their concentration in nanofluids and did not consider the movements of solid and liquid atoms and their possible collisions which can transport heat in nanofluids and may leads to increased TC. Several mechanisms and analytical models have been proposed there after in the literature for explaining the enhanced conductivities of the nanofluids [6-8]. The earliest large scale microscopic simulation is performed [9] using Brownian dynamics. A better alternative is to employ interatomic potentials and perform true molecular dynamics (MD) simulations. As MD simulations accurately calculates the movements of the particle in the molecular level, the same simulation with statistical mechanics can predict most accurate transport phenomena in nanoscale compared to any model based on continuum mechanics. In MD simulations the TC can be computed either using non equilibrium MD (NEMD) or equilibrium MD (EMD or Green-Kubo method). The Green-Kubo approach is an EMD method that uses heat current fluctuations to compute the TC via the fluctuation-dissipation theorem. In this study, a
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