Heat Transfer Enhancement of Phase Change Materials for Thermal Energy Storage Systems

Abstract

In recent studies, the energy storage capability of phase change materials (PCMs) in thermal energy storage systems, such as in the case of solar water heaters has attracted many attentions; however, PCMs may not be fully effective due to their poor heat transfer characteristics, namely thermal conductivity. This study aims to explore the thermal performance of heat transfer materials to be applied in conjunction with PCMs. The selected types of PCMs are paraffin waxes with melting point temperatures of 28-72◦C. In an effort to study both convective and conductive heat transfer enhancement the experimental analysis has been divided into two phases. In the first analysis, silicone oil is selected as a heat transfer medium to be used with the PCMs to establish convective heat transfer enhancement. The melting point, latent heat and specific heat capacity were measured by a differential scanning calorimeter (DSC). The obtained results show that silicone oil will lead to melting point depression of maximum 3◦C in the PCMs. In the second analysis, the conductive heat transfer enhancement by addition of nanoparticles has been investigated. The selected nanoparticles for this analysis are Aluminum Oxide (Al2O3), Cupric Oxide (CuO), Titanium Oxide (TiO2) and Multi-Walled Carbon Nanotubes (MWCNT). The nanoparticles displayed capabilities of increasing the specific heat capacity by up to 46.15%. The micro-structure of the nano-enhanced PCMs was analyzed using SEM technology to observe the effectiveness of the dispersion process of the nanoparticles into the PCM. The obtained results from this study show thermal performance improvement of PCMs, which is expected to lead to overall efficiency improvement in thermal energy storage systems.