Study on Enhanced Heat Transfer Characteristics of Carbon-Based Network Composite Phase-Change Microcapsules

Organic phase-change materials (PCMs) suffer from problems such as easy leakage from the matrix and low thermal conductivity in the molten state. Encapsulating PCMs in the form of microcapsules is an effective method of addressing these issues. In this study, modified phase-change microcapsules with paraffin as the core material, melamine-formaldehyde resin as the wall material, flake graphite (FG), multilayer graphene (GNP), or expanded graphite (EG) as heat conducting additives were prepared by in situ polymerization. The surfaces of the microcapsules were smooth and spherical. With an increase in the mass fraction of the carbon additive, the thermal conductivity of the phase-change microcapsule composite PCM gradually increased, where the heat transfer properties were most significantly enhanced in the case of the EG/MPCM composite PCM, with a thermal conductivity of 1.9 W/(m·K), which is 9.5 times that of pure paraffin. The addition of FG, GNP, and EG had little effect on the latent heat of the phase-change microcapsules, where the latent heat retention rates of the composites were 83.8, 78.8, and 86.4%, respectively. As the content of the carbon additive increased, the three transitional stages (preheating, phase change, and overheating) all occurred earlier compared with those of the pure phase-change microcapsules, and the time required for latent heat release was clearly reduced in the composites. Therefore, introducing a carbon additive into phase-change microcapsules can improve the heat transfer capacity and energy storage efficiency.