Heat Transfer Performance of Biphilic Surfaces With Diatomite‐Based Composite Coatings in a Closed Thermosyphon System

ABSTRACT This study investigates the thermal performance of innovative biphilic boiling surfaces designed for CPU cooling applications using a two‐phase closed thermosyphon (TPCT) system. The surfaces were fabricated by applying composite coatings—comprising epoxy resin and diatomite particles functionalized with APTES and PFOTS silanes— onto Al1050 aluminum alloy substrates via dip‐coating. These coatings produced superhydrophobic regions embedded within a hydrophilic base, forming biphilic surfaces with distinct geometries. Pool boiling experiments demonstrated that the biphilic configurations significantly outperformed the smooth reference surface in terms of heat transfer performance. The optimal liquid filling ratio was determined to be 30%. The best performance was achieved by the BI4R surface, featuring four 4 mm‐diameter superhydrophobic circular regions, followed closely by the BI2R configuration. The BI4R biphilic surface achieved a heat transfer coefficient of 0.684 W/cm 2 ·K, representing a 1.65‐fold increase compared with the smooth boiling surface. Furthermore, the BI4R surface exhibited the lowest overall thermal resistance among all tested configurations—0.488 W/°C at the maximum applied heat load of 110 W. The results indicate that both the geometry and ratio of superhydrophobic area critically influence the overall thermal resistance, with excessive hydrophobic coverage potentially reducing performance. These findings highlight the potential of diatomite‐based biphilic coatings to enhance heat dissipation in compact electronic cooling systems.