Thermal transfer characteristics of a phase change composite heat sink based on π-shaped graphene foam with high thermal conductivity and rapid response

Solid–liquid transition is characterized by high thermal storage density and near-isothermal endothermic/exothermic processes. Consequently, phase change heat sinks (PCHSs) based on phase change materials hold significant potential for application in heat management of electronic devices under specialized operating conditions. However, existing research still confronts key challenges, including insufficient in-plane thermal conductivity, slow thermal response rates, and inadequate investigation into the effects of encapsulation materials. In this study, a n-octacosane/π-shaped graphene foam (n-octacosane/π-GF) phase change composite (PCC) heat sink is proposed. This design enables rapid in-plane heat spreading while facilitating efficient heat transfer and storage along the thickness direction, thereby synergistically optimizing heat spreading, transfer, and storage performance. Comparative analyses were conducted to evaluate the heat transfer characteristics in both in-plane and thickness directions and the thermal management performance of different PCHSs. The integration of aluminum–graphite composite and π-GF was found to enhance the in-plane heat spreading capability and through-thickness heat transfer performance of the PCHS, mitigate in-plane heat accumulation, accelerate the melting of n-octacosane along the thickness direction, and reduce the heat storage duration of n-octacosane. With increasing heat flux density, the safe operating time initially decreases sharply before entering a phase of gradual decline. Relative to pure n-octacosane, the n-octacosane/π-GF composite exhibits a 13-fold enhancement in the through-thickness thermal conductivity and a 110-fold improvement in the in-plane thermal conductivity, with the latter reaching 18.8 W·m⁻¹·K⁻¹. Furthermore, the thermal management performance of the n-octacosane/π-GF PCC encapsulated with aluminum–graphite composite is 2.9 times higher than that of the aluminum alloy encapsulated pure n-octacosane PCHS. This work offers meaningful insights for the design of PCHSs with rapid response and high in-plane thermal conductivity, as well as for the rational selection of encapsulation materials.