Optimal Thermal Design of a Micro Pin-Fin Heat Sink Using Hybrid Fin Heights and Various Perforated Fin Shapes

This study presents a numerical optimization framework for a micro pin-fin heat sink (MPFHS). Three-dimensional conjugate heat transfer and fluid flow are simulated using the commercial CFD code CFD-ACE+. Coupled with the Levenberg–Marquardt method (LMM), the geometric parameters are optimized to minimize the base wall temperature Tbw under a constant total fin-volume constraint. The investigation assesses four pin-fin architectures—solid square (MPFHS-S), solid cylindrical (MPFHS-C), perforated square (MPFHS-SP), and perforated cylindrical (MPFHS-CP)—across five distinct fin-height distributions: uniform, constant-step (Design #1), increasing-step (Design #2), decreasing-step (Design #3), and hybrid-step (Design #4). The results demonstrate that perforated fins significantly enhance heat transfer by disrupting the thermal boundary layer and mitigating heat accumulation in the wake region. Within the allowable geometric constraints, larger perforation radii provide superior cooling performance. Among all examined configurations, the LMM-optimized Design #4 consistently achieves the lowest base temperature across the entire Reynolds number range. Specifically, for the MPFHS-CP configuration, the optimized Design #4 yields Tbw values of 326.279 K, 311.617 K, and 309.142 K at Reynolds numbers of 200, 800, and 1200, respectively. As the Reynolds number increases, the temperature differences among the configurations gradually diminish, indicating that forced convection increasingly dominates the flow and reduces the sensitivity to fin geometry. Pressure-drop analysis reveals that perforated configurations incur an approximate 10–15% higher pressure loss compared to their solid counterparts. To evaluate the overall thermo-fluid behavior, the thermal performance factor η is employed to evaluate the trade-off between heat transfer enhancement and the associated pressure-drop penalty. The results confirm that cylindrical fins consistently outperform square fins, with perforations providing an additional reduction in Tbw. Overall, combining a hybrid fin-height distribution with perforated pin fins presents an effective strategy for optimizing MPFHS performance, offering practical guidelines for the thermal management of high-power electronic devices.