Investigation of the impact of graphite microparticle geometry on thermal performance enhancement of phase change materials (PCMs) for thermal energy storage

Phase change materials (PCMs) offer high energy storage densities but suffer from inherently low thermal conductivities, which limit their efficiency in thermal storage and management applications. This study aims to improve the thermal performance of PCMs through the incorporation of graphite microparticles and to assess the impact of particle shape and interfacial resistance when modeling effective thermal conductivity. Two PCM composites were developed: paraffin RT55–graphite and the second is eco-friendly beeswax–graphite, each containing 10 wt% of graphite microparticles. Experimental characterizations were conducted using Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), the Hot-Disk method and Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) A numerical model based on a Representative Volume Element (RVE) approach was developed in ANSYS software to predict the effective thermal conductivity of the composites. Simulations revealed that graphite particle thermal conductivity and geometry significantly influence heat transfer. For spherical particles, changing the particle diameter had a negligible effect on thermal conductivity due to their isotropic geometry. Furthermore, particle shape played a crucial role: disk-like particles yielded the closest agreement with experimental results, with a deviation below 2% for the beeswax composite. The aspect ratio of disk-like particles strongly influenced the effective thermal conductivity. The impact of interfacial thermal resistance (ITR) between graphite and PCM on the final effective thermal conductivity of composite was also studied. Overall, the combined experimental and numerical investigations demonstrate that particle geometry strongly governs the effective thermal conductivity of PCM composites. The beeswax–graphite composite, in particular, presents a promising, sustainable alternative for thermal energy storage and management applications.