Heat Transfer and Irreversibility Analysis of Cu-MXene/Water Hybrid Nanofluids in Tubes with Partial Metal Foam Filling

Metal foams and nanofluids are recognized as attractive and effective heat transfer enhancement methods. This study numerically investigates forced convection heat transfer and second-law thermodynamic behavior of water and a 0.02% Cu–MXene/water hybrid nanofluid flowing through a tube partially filled with metal foam. Three configurations are examined: a clear tube as the reference case; Case A (three discrete foam blocks occupying 3/16 of the tube length); and Case B (a single block occupying 9/16), using four metal-foam types (aluminum 30/45 PPI, copper 40 PPI, and nickel 60 PPI). The governing equations are solved using the finite-volume method with the SIMPLER algorithm and validated against published experimental and numerical data. Results show that Case B provides higher heat-transfer rates and performance evaluation criterion (PEC) values than Case A, although at the expense of larger pressure-drop and pumping-power penalties. The highest heat-transfer enhancement is obtained with Cu-40 PPI foam and the hybrid nanofluid in Case B, where the average Nusselt number increases by a factor of 3.33 at a Reynolds number of Re = 200 relative to water in the clear tube. Higher-thermal-conductivity foams, combined with the hybrid nanofluid, provide greater thermohydraulic benefits than lower-conductivity foams with water. The second-law analysis reveals that increasing Re reduces thermal irreversibility but increases frictional irreversibility, highlighting the competing effects of heat-transfer enhancement and hydraulic resistance. Overall, the Cu-40 PPI/hybrid nanofluid combination in Case B at low Re provides the most favorable performance among the investigated conditions.