Enhanced flow boiling of HFE-7100 on graphene-coated sintered copper surfaces: combined effects of particle size, shape, and pore structure

Official URL: https://dx.doi.org/10.1016/j.ijheatmasstransfer.2026.128724

This study investigates the effect of copper particle size, shape, and graphene coating on flow boiling of HFE-7100 in a high-aspect-ratio rectangular minichannel. Six porous copper surfaces were fabricated by sintering spherical or irregular particles ranging from fine to coarse ones (70 - 250 µm) and by selectively coating them with graphene using the Chemical Vapor Deposition (CVD) technique. The performance of each surface was evaluated based on heat transfer coefficient (HTC), wall superheat, and exit vapor quality at a fixed mass flux of 120 kg/m²·s and heat fluxes up to 19.1 W/cm². The results show that surfaces composed of medium-sized irregular particles (#S3 and #S4) significantly outperform fine and coarse particle configurations. The addition of graphene further enhances flow boiling heat transfer, with #S4 achieving an HTC of 1.15 W/cm²·K, an improvement of 36% compared to its uncoated counterpart #S3 and 105% over the coarse particle surface #S5. Graphene-coated surfaces also reduced required wall superheat by up to 8.2°C at a heat flux of 19.1 W/cm². Flow visualization and single bubble tracking reveal that the medium-sized irregular particles support faster bubble growth and larger bubble diameters due to better vapor escape and heat spreading. These findings highlight the importance of optimizing both microstructure and surface conductivity in designing high-performance cooling surfaces for boiling heat transfer applications involving dielectric fluids.