Superior Thermal Conductivity and Charging Performance of Zinc Oxide Dispersed Paraffin Wax for Thermal Energy Storage Applications

Organic phase change materials (PCM) such as paraffin wax have lower thermal conductivity, compromising the rate of heat transfer during charging and discharging. This work reports the improvement of the thermal conductivity of paraffin wax through dispersion of ZnO nanoparticles and its outcome in terms of heat transfer performance. ZnO-paraffin wax (ZnO-PW) nanocomposites were made by dispersing ZnO nanoparticles in paraffin wax. An increase in thermal conductivity (76.4% for 10 wt. % nanocomposite) and reduction in specific heat (10.7% for 10 wt. % nanocomposite) upon nanoparticles' addition to paraffin wax were observed. In a first-of-its-kind work, we manifested that the improved thermal conductivity of ZnO-PW nanocomposites, combined with potential improvements in liquid-phase thermal conductivity, resulted in a 96% increase in the PCM side heat transfer coefficient in a tube-in-shell thermal energy storage unit operating under constant heat transfer fluid temperature. Thus, our findings clearly show an increase in the thermal energy storage performance of a latent heat thermal energy storage system (LHTES) using ZnO-PW nanocomposites as the energy storage medium.