Presented are the results of a 3-D numerical analysis of a composite heat spreader for immersion cooling of a 20 × 20 mm microprocessor. The spreader is comprised of two 0.5 mm thick Copper (Cu) laments separated by a layer of highly ordered pyrolytic graphite (HOPG), 0.25-1.0 mm thick. The exposed surface of the top Cu lament has an average roughness, Ra = 1.79 μm and is cooled by saturation nucleate pool boiling of PF-5060 dielectric liquid. Investigate is the impact of δ_(HOPG) on the total power removed, the maximum temperature of the underlying chip, T_(max), and mitigating the chip hot spots. Increasing δ_(HOPG) increases the total power removed, but also increases T_(max). The spreader with a 1.0 mm-thick δ_(HOPG) is capable of removing 318 W, without exceeding 90% of the critical heat flux (CHF), at T_(max) = 120°C. This power removal is significantly higher than that with an all Cu spreader of the same thickness of 90 W, but at much lower T_(max) of 67°C. Composite spreaders with δ_(HOPG) = 0.25, 0.5, and 0.75 mm are capable of removing up to 160 W at T_(max) = 85°C, 228 W at 100°C, and 292W at 115°C, respectively. The HOPG suppresses the transmission of hot spots to the spreader surface and increasing δ_(HOPG) does not mitigate the hot spots.
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