Molecular dynamics of interfacial heat transfer in metal/non-metal nanofluids on Cu-graphene composite porous substrates

Addressing the thermal management bottleneck in advanced chip technologies requires a fundamental understanding of phase-change phenomena. This study employs molecular dynamics simulations to systematically investigate the phase-change heat transfer regulation mechanisms in porous graphene-nanofluid composite systems, with a focused comparative analysis on the distinct dynamic behaviors between non-metallic nanofluids (graphene-based) and metallic nanofluids (copper-based) during heating-phase boiling and cooling-phase condensation. By establishing a Cu-graphene composite porous substrate integrated with both nanofluid types, we demonstrate that pore confinement significantly optimizes nucleation dynamics. Graphene-lined pore configurations (Nx-in) accelerate nucleation initiation by 64.7 % compared to a flat structure. Additionally, graphene nanofluids reduce nucleation barriers through nanosheet-induced microvortices. This synergy results in a heat transfer efficiency of 66.28%, which is 6.2 % higher than that of the bare copper substrate. In contrast, copper nanofluids exhibit localized thermal resistance due to nanoparticle agglomeration. During cooling, graphene nanosheets form suspended droplets with a diameter of approximately 50 Å, acting as condensation nuclei. Meanwhile, copper agglomerates immobilize over 80 % of the liquid phase near the wall, reducing thermal dissipation efficiency. Thermal flux orientation governs phase transition modes: axial temperature gradients in Nx-in configurations promote longitudinal fluid fragmentation, whereas restricted lateral heat dissipation in Nx-out systems triggers multicentric fragmentation. The study further reveals interfacial processes as dominant factors in nonequilibrium heat transfer, with graphene nanofluids synergistically enhancing substrate wettability and evaporation kinetics. These findings provide an atomic-scale theoretical framework for material selection (metal/non-metal nanofluid compatibility) and structural optimization in high-power chip thermal management and condenser design.