Thermal convection and melting dynamics in a Phase Change Material (PCM) embedded in a porous solid foam

Solid-liquid Phase Change Materials (PCMs) are key components in thermal energy storage thanks to their ability to store and release large amounts of energy through latent heat. They are often embedded in macroscopic porous structures to prevent leakage, enhance heat transfer, and improve solidification. The resulting composite systems exhibit thermal behaviors governed by the geometry and thermal properties of the porous matrix, the evolution of PCM thermophysical properties during phase change, and the dominant heat-transfer mechanisms. Despite their relevance, detailed studies of convection-driven melting in PCM-saturated porous media remain limited because measurements in opaque materials are difficult to perform without disturbing the system. To address this issue, we use Magnetic Resonance Imaging (MRI) to investigate a paraffin embedded in a highly porous foam disk whose thermal conductivity is comparable to that of the PCM. The system is subjected to constant heating at the bottom and cooling at the top, allowing stationary melt fronts to develop. Thanks to MRI’s ability to track the melting interface within the bulk and measure fluid velocities, our experiments show that convection generates a wavy melting interface and significantly enhances melting, producing liquid heights more than twice those obtained under conduction. Flow-field measurements reveal convection patterns ranging from cross-rolls to hexagonal and square cells, with local velocities strongly influenced by the porous geometry. Heat-transfer analysis shows that a clear Nusselt-Rayleigh trend emerges when the data are rescaled to include both the temperature difference ratio between solid and liquid PCM and the relative thicknesses of these layers. This provides a basis for future studies of coupled convection and phase change in porous media, including systems with mushy layers or porous structures with different geometries and thermal-physical properties.

Work In Progress