Enhancing latent heat storage dynamics with expanded graphite foam: Myth vs. reality check through numerical and experimental investigations

The solid–liquid phase transition, with its moderate latent heat absorption or release over a narrow temperature margin and minimal density difference, finds extensive use in various thermal engineering applications such as energy storage, electronics cooling, and personal cooling. Commonly used organic or inorganic phase change materials (PCM) suffer from low thermal conductivity, which can be addressed by composite PCMs (CPCM). CPCMs comprise highly porous compressed-expanded graphite (CEG) foam impregnated with PCM. While CPCM shows significantly improved thermal conductivity, porous CEG foam in CPCM suppresses free convection during the melting process, making the heat transfer mostly diffusion-dominated. Our study compares free convection-dominated melting of pure PCM with diffusion-dominated melting of CPCM, conducted through numerical and experimental analysis in a bottom-heated rectangular cavity. From this investigation, we find that CPCM offers significantly better temperature uniformity, leading to the eradication of potential hot spots, and is advantageous for heat sink applications. However, CEG volume fraction in CPCM above or below a specific range hampers the fast melting process in thermal storage applications in contrast to the conventional notion.