The design freedom brought by additive manufacturing (AM) can be leveraged in the design of microchannel heat sinks to improve their cooling performance. The permeable membrane microchannel (PMM) heat sink geometry was inspired by the ability of powder bed AM processes to fabricate partially porous metal parts having small internal flow features on the order of the powder size. The design routes coolant through a parallel array of thin permeable membranes arranged in a single-layer-manifold configuration. The permeable membranes provide effective heat exchange surfaces and the manifold configuration yields a low flow resistance across the PMM heat sink, all incorporated in a single layer by the use of AM. Past work has introduced the PMM heat sink concept, but the optimal geometric feature sizes were not explored or identified. The n current study is first to explore design optimization of the PMM heat sink to identify target feature sizes for AM fabrication, assessment of the conditions under which the PMM geometry outperforms other standard microchannel heat sink designs, and inspection of the ability of metal 3D printing process to produce the optimal features. To this end, a reduced-order PMM heat sink model is developed, a gradient-based-multi-objective optimization is performed to identify the optimal feature sizes for different coolants (water and 48/52 water/ethylene glycol mixture) at different flow rates (100 – 500 mL/min), footprint areas (49 – 900 mm2), and channel heights (0.5 – 2.5 mm). The optimization results are benchmarked against an optimized straight microchannel (SMC) heat sink design. Optimized PMM designs offer up to 68% lower thermal resistance at a set pressure drop compared to optimized SMC designs. A pair of SMC and PMM heat sinks optimized for the same operating conditions are 3D printed using direct-metal-laser-sintering (DMLS) of AlSi10Mg. X-ray microtomography is used to characterize the geometry of the 3D-printed parts. The model identifies that optimal membrane gap sizes on the order of ~10s μm are required for the PMM to realize performance advantages compared to SMC heat sinks under the same operating conditions. The performance is predicted to be highly sensitive to this pore size, and even though DMLS is shown to produce parts with gaps as small as 26.7 microns, morphological deviations between the design and as-printed part are shown to lead to noticeable performance differences. Albeit excellent performance potential reinforced by this work, these findings call for further AM process development to ensure reliable, as-predicted PMM heat sinks to realize this potential.
Date of this Version
S. Ozguc, L. Pan, and J.A. Weibel, Optimization of permeable membrane microchannel heat sinks for additive manufacturing, Applied Thermal Engineering 198, p. 117490, 2021.