Hierarchically Structured Laser-Induced Graphene for Enhanced Boiling on Flexible Substrates

Thermal management problems in high-power flexible electronics are exacerbated by the design complexity and requirement of stringent temperature control to prevent skin burns. Thus, effective heat dissipation methods applicable to flexible electronics on polymer substrates are an essential device design component. Accordingly, this study investigates the pool boiling heat transfer characteristics and potential enhancements, enabled by laser-induced graphene (LIG), which is both highly porous and bendable. Patterned LIG with a mesh spacing of 200 μm was formed on flexible polyimide substrates by laser direct writing, and the resulting surfaces exhibited enhanced heat transfer characteristics. Pool boiling experiments were conducted with an FC-72 working fluid to investigate the heat removal capability of LIG, and its performance was further improved by separating the liquid supply passages from the vapor escape routes. Overall, the inclusion of LIG resulted in a 2- to 3-fold increase in both the critical heat flux (33.6 W/cm2) and heat transfer coefficient (7.6 kW/(m2·K)), compared to pristine polyimide films.