Effects of various carbon nanofillers on the thermal conductivity and energy storage properties of paraffin-based nanocomposite phase change materials

The effects of adding various carbon nanofillers on the thermal conductivity and energy storage properties of paraffin-based nanocomposite phase change materials (PCMs) for thermal energy storage were investigated experimentally. These included short and long multi-walled carbon nanotubes, carbon nanofibers, and graphene nanoplatelets (GNPs). For each type of the nanofillers, nanocomposite PCM samples with mass concentrations of 1–5wt.% at an increment of 1wt.% were prepared. The thermal conductivity of the samples in solid phase was measured using the transient hot-wire method at elevated temperatures. The energy storage properties, including melting/solidification temperatures and enthalpies, were measured using a differential scanning calorimeter. It was shown that the presence of the nanofillers slightly decreases the phase change enthalpies and has negligible influence on the phase change temperatures. The thermal conductivity of the nanocomposite PCMs was found to increase with raising the loading, while the relative enhancement strongly depends on the size and shape of the nanofillers. Of the four types of carbon nanofillers examined, GNPs were observed to cause greatest relative enhancement up to 164% at the loading of 5wt.%, due to their two-dimensional planar structure that leads to reduced filler/matrix thermal interface resistance, in contrast to the moderately decreased energy storage capacity of GNP-based nanocomposite PCMs.