In this paper, we investigated the thermal conductivity of three-dimensional nanocomposites composed of randomly distributed nanoparticles with large thermal conductivity differences in the constituents. Nanoparticles in composite materials fabricated by processes such as hot press or spark plasma sintering tend to be randomly distributed. For composites made of particles with high thermal conductivity contrast ratio, percolation theory predicts the existence of a continuous phase of high thermal conductivity material when its volumetric concentration reaches beyond the percolation threshold. Such a continuous phase can provide a low resistance pathway for phonon transport in the nanocomposites. Therefore, the thermal conductivity of the composites is expected to increase significantly with increasing concentration of the high thermal conductivity nanoparticles. However, when the characteristic size of the nanoparticles is comparable or smaller than the phonon mean free path, the interface between two materials causes phonon scattering and significant thermal resistance in the highly conductive phonon pathway. Such an additional thermal resistance can reduce the magnitude of the thermal conductivity improvement in the nanocomposites. In this study, the Monte Carlo simulation was employed to generate the nanoparticle random distribution and to simulate phonon transport in the nanocomposites. The effects of particle size, thermal conductivity contrast and interface characteristic on thermal conductivity of the nanocomposites are discussed.

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