Constrained melting of graphene-based phase change nanocomposites inside a sphere

In the present work, the melting behavior of a fatty acid-based phase change material (PCM) with the addition of functionalized graphene nanoplatelets in a spherical capsule was experimentally studied. The fatty acid-based PCM (OM 08) has been selected for the air-conditioning application with a phase change temperature of 8 °C. The PCM-based nanocomposite samples were prepared by covalent functionalization method. The volume percentage of the functionalized graphene nanoplatelets varied from 0.1 to 0.5% with an increment of 0.1%. The thermal conductivity and rheological properties of the PCM nanocomposites were measured experimentally by transient hot wire method and rheometer, respectively. The maximum enhancement in thermal conductivity for 0.5 vol% of graphene nanoplatelets was found to be ~ 102%. The rheological test found that the addition of graphene nanoplatelets in the PCM resulted in the transition of Newtonian behavior to non-Newtonian behavior at lower shear rates. The viscosity of the PCM nanocomposites increases with volume fraction. Initially the pure PCM and PCM nanocomposites were solidified individually in a spherical capsule at different bath temperatures of 2 °C and − 10 °C. Then the solidified samples were kept in a constant temperature bath at 31 °C, and the melting characteristics were studied. The melting time of the PCM nanocomposite was reduced significantly with the addition of 0.5 vol% of graphene nanoplatelets by ~ 26% and ~21% for the PCM initial temperature of − 10 °C and 2 °C, respectively.