A Streamwise Partitioned Variable-Density Plate-Fin Heat Sink for Downstream Thermal Bottleneck Mitigation with Improved Temperature Uniformity

When multiple heat sources are arranged sequentially along the airflow direction in power electronic equipment, streamwise air heating weakens the downstream heat-transfer driving force, causing outlet-side hot spots and temperature non-uniformity. Building on established variable-density concepts, this study develops a streamwise partitioned variable-density (SPVD) plate-fin heat sink for sequentially arranged heat sources. Within the same installation envelope, an inlet low-fin-density region preserves flow-through capacity, while a downstream high-fin-density region strengthens cooling near the thermal bottleneck. A three-dimensional steady-state conjugate heat-transfer model was calibrated against experimental data. The partition ratio, inlet fin number, and downstream channel densification coefficient were optimized using a geometry-feature-enhanced Kriging surrogate coupled with NSGA-II, with maximum temperature, pressure drop, and mass as objectives. The maximum inter-source temperature difference, ΔT, was retained as a uniformity metric rather than an optimization objective because a small ΔT alone does not ensure hot-spot safety. Compared with full-length uniform-fin configurations having the same total fin number, representative SPVD designs reduced maximum temperature by 8.43%–13.74%, pressure drop by 11.36%–28.61%, mass by 20.90%–24.33%, and ΔT by 66.38%–84.12%. Near-equal-mass benchmarks further showed 15.39%–17.77% lower maximum temperature and 65.65%–84.50% lower ΔT, accompanied by a 14.07%–32.83% pressure drop penalty. Off-design simulations under downstream-biased heat loads also retained the maximum-temperature advantage. Under the investigated conditions, these results show that streamwise fin-density partitioning redistributes cooling capacity, mitigates downstream thermal bottlenecks, and improves inter-source temperature uniformity without relying on additional material.