Multiwalled CNT and graphene nanoplatelets based nano-enhanced PCMs: Evaluation for the thermal performance and its implications on the performance of hybrid PV/thermal systems

The low heat conductivity of paraffin-based phase change materials (PCMs) makes them unsuitable for several practical uses. Carbon-based nanomaterials with high thermal conductivity have demonstrated promising results in improving the thermal characteristics of various fluids and PCMs. Among the different carbon-based nanomaterials, Multi-Walled Carbon Nanotubes (MWCNT) and Graphene Nanoplatelets (GNP) are chosen for this study to enhance the thermal performance of paraffin wax (PW) n a comparative study. Different wt% of nanomaterials were mixed with PW to prepare two distinct sets of nano-enhanced phase change materials (nanoPCMs). The prepared samples were characterized and their thermal properties were measured. A numerical model was developed using the experimentally measured properties to evaluate the impact of the nanoPCMs on the performance of a hybrid PV/Thermal system. The majority of the PW/MWCNT samples improved their thermal conductivity more than the PW/GNP samples, whereas the PW/GNP samples attained higher specific heat values. During melting and at 5% wt, the PW/MWCNT demonstrated a thermal conductivity enhancement of 13.9%, compared to 3.8% for the PW/GNP, both at 25 °C. At the same concentration, the specific heat of PW/GNP was higher than that of PW/MWCNT by 6.7%. On the other hand, when repeatedly cycled, the nanoPCMs samples displayed good thermal stability. Numerical analysis of the performance of a hybrid PV/Thermal system with the PW/GNP layer on the back showed superior cooling for the PV panel with an improved electrical and thermal efficiency.