Increased thermal conductivity of liquid paraffin-based suspensions in the presence of carbon nano-additives of various sizes and shapes

The effect of adding carbon nanomaterials on the thermal conductivity of liquid paraffin-based suspensions was investigated. These included pristine and carboxyl-functionalized short multi-walled carbon nanotubes (MWCNTs), long MWCNTs, carbon nanofibers, and graphene nanoplatelets (GNPs). The thermal conductivity of the suspensions was measured using the transient hot-wire method at a constant temperature. The size, shape, and dispersion of the carbon additives were observed by microscopy, and the stability and viscosity of the suspensions were also characterized. It was shown that thermal conductivity of the suspensions increases with increasing the loading of the carbon additives and the extent of relative increase depends strongly on their size and shape. Of the various carbon nanomaterials examined, GNPs caused greatest increase due to reduced thermal interface resistance associated with their two-dimensional planar structure. The viscosity of GNP-based suspensions decreases at relatively high loadings, whereas a monotonic increase was observed for suspensions with all the other carbon additives.