Numerical modeling of the flow direction effect on heat sinks equipped with fin and foam

The ongoing miniaturization of electronic devices imposes design limitations on the placement of cooling fans in active heat sinks. This work investigates thermal and hydrodynamic performance in different flow configurations of impinging, parallel, and induced flow for three distinct heat sinks, including plate-fin, metal foam, and hybrid. Numerical modeling of the flow field with computational fluid dynamics employed the local thermal non-equilibrium (LTNE) approach and the standard k-ε model for heat transfer and turbulence. The results indicate that flow directionality significantly influences both heat transfer and pressure characteristics. Specifically, the Nusselt number increased by 62.86% and 46.51% for the plate-fin, 35.6% and 37.6% for the metal foam, and 42.59% and 31.17% for the hybrid model under induced and impinging flow conditions, respectively, when compared to parallel flow. Impinging flow resulted in the highest pressure drop in all cases, whereas parallel flow exhibited the lowest pressure drop. Evaluation based on the Figure of Merit (FOM) revealed that impinging flow significantly degraded overall performance, reducing FOM by 40.44% (plate-fin), 36.7% (metal foam), and 41.51% (hybrid). In contrast, induced flow consistently improved thermo-hydraulic efficiency, increasing the FOM by 17.38%, 15.95%, and 76.6%, respectively. Overall, the comparative analysis highlights that flow directionality plays a decisive role in determining the balance between heat transfer enhancement and hydraulic penalty in compact heat sink systems. While impinging flow promotes strong local convection, the associated pressure drop can compromise overall efficiency. In contrast, induced flow provides a more favorable trade-off between thermal improvement and pumping power requirements, particularly in hybrid configurations. These findings offer practical design guidance for airflow arrangement in space-constrained electronic cooling applications and emphasize the importance of simultaneously evaluating thermal and hydraulic metrics when selecting optimal heat sink configurations.