Enhanced through-plane heat transfer in polymer composites with magnetically aligned graphene and hBN fillers for heat exchangers

Thermally conductive composite materials combining polymer matrix reinforced with carbon fiber have attracted considerable interest for use in heat exchangers. This study focuses on improving through-plane thermal conductivity by incorporating magnetically responsive fillers into polymer composites. Graphene flakes and hexagonal boron nitride (hBN) platelets were coated with iron oxide, creating magnetized fillers. Both these modified and unmodified fillers were embedded into epoxy resin at concentrations up to 4 wt%. Successful magnetization was confirmed by FE-SEM, XRD with indexed Fe₃O₄ peaks, and EDS elemental mapping. During composite fabrication, an external magnetic field was applied to vertically align the magnetic particles in the epoxy matrix. This alignment occurred owing to dipolar magnetic interactions, which promoted particle aggregation into columnar formations. These structures substantially improved thermal conductivity compared to samples with randomly dispersed fillers. At low filler loadings, the composites showed considerable improvements in heat conduction; however, higher filler concentrations caused dispersion difficulties that limited further improvement. Additionally, in carbon-fiber-reinforced polymer (CFRP) systems, factors such as fiber spacing, particle shape, and aspect ratio were critical in achieving effective filler alignment. Therefore, accurate control of these parameters is essential to fully realize the thermal performance of CFRP composites.