Melting characteristics and heat storage/release mechanisms of millimeter-scale glass spheres encapsulated phase change materials

This study bridges critical research gaps in millimeter-scale glass sphere encapsulated phase change materials (GSPCM), where previous work has been limited by: insufficient understanding of heat transfer mechanisms in the 1-10 mm size range that balances structural integrity and thermal response, and absence of validated models accounting for concurrent conduction-convection-phase change interactions. Paraffin-air GSPCM systems (6–10 mm diameter, >75% PCM loading) were analyzed using coupled experimental and computational fluid dynamics (CFD) approaches, revealing three distinct melting regimes: conduction-dominant (0-20s), transitional (20-40s), and convection-dominant (40-98s). High-speed thermal imaging uncovers a "dual-vortex" flow pattern that enhances heat transfer by 38-42% compared to pure conduction - a phenomenon previously unreported for this scale. Key advancements include that diameter-dependent scaling laws showing R 3 volumetric storage (10mm stores 403.79% more than 6mm) versus R 2 heat transfer rates (peak 0.6696 J/s at 50 °C). A validated VOF-enthalpy model (error<5%) capturing multiphysics interactions (conduction-convection-volume change). In addition, it has also been found that increasing the temperature difference can shorten the time and reduce the heat release rate. This offers guidance for millimeter-scale encapsulated PCM applications and heat transfer studies.