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 δHOPG on the total power removed, the maximum temperature of the underlying chip, Tmax, and mitigating the chip hot spots. Increasing δHOPG increases the total power removed, but also increases Tmax. The spreader with a 1.0 mm-thick δHOPG is capable of removing 318 W, without exceeding 90% of the critical heat flux (CHF), at Tmax = 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 Tmax of 67°C. Composite spreaders with δHOPG = 0.25, 0.5, and 0.75 mm are capable of removing up to 160 W at Tmax = 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 δHOPG does not mitigate the hot spots.

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