Multiscale study of thermal conductivity of boron nitride nanosheets/paraffin thermal energy storage materials

Dispersion of nanofillers into phase change materials is found to be useful for improving the thermal conductivity (TC) of materials. To achieve a high TC of composites, the geometry factors of nanofillers should be considered. In this paper, classic molecular dynamic simulations and theoretical analysis model based on the effective medium theory were adopted to investigate the effect mechanism of layer number and size of hexagonal boron nitride nanosheets (h-BN) on TC of h-BN/paraffin composites. Research results showed that TC of the encased h-BN is lower than that of the suspended one due to the suppression ofparaffin. Along with the rise of layer number, the phonon vibrational power of h-BN is partially recovered, which results in the increase of TC of h-BN and the decrease of interfacial thermal resistance of h-BN/paraffin. With the size of 5 mu m, the volume fraction of 5% andlayer number of 15, TC of h-BN/paraffin composites increases to 1.5 W/m.K by nearly 6 times compared with paraffin. To obtain a high TC of composites, layer number and lateral size of h-BN must be simultaneously increased. This finding is a guide for using multi-layer nanosheets as thermal conductive fillers in the field of enhanced heat transfer.