Thermal conductivity enhancement of phase change materials using a graphite matrix

The thermal conductivity of paraffin wax was increased by two orders of magnitude by impregnating porous graphite matrices with the paraffin. The graphite matrices were fabricated by compacting flake graphite that had been soaked in a bath of sulfuric and nitric acid then heat-treated at 900 °C. The properties of the graphite matrix and paraffin phase change material (PCM) composites were measured for graphite matrix bulk densities ranging from 50 g/L to 350 g/L. The properties studied include the thermal conductivity in directions parallel and perpendicular to the direction of compaction, paraffin mass fraction, and the latent heat of fusion of the composite samples. The latent heat of fusion and phase change characteristics of the graphite/paraffin composites were studied using differential scanning calorimetry (DSC). Scanning electron microscope (SEM) pictures are included to visualize the morphology of the graphite during each stage of the composite fabrication process. The performance of the PCM-composite was demonstrated by using the PCM-composite as a passive thermal management system for a lithium ion battery pack discharged at high rates.