Local flow boiling performance comparison of two increasing density heatsinks

Flow boiling is a promising cooling technique for next-generation thermal management due to its high heat flux capability and improved temperature uniformity. Variable density heatsinks have emerged as a cooling design strategy for their ability to redistribute two-phase flow and enhance flow stabilization. This experimental work tested two novel microstructured designs: increasing variable density pin-finned surface (PF) and a short stepwise varying width microchannel configuration (S-SVW-Mchs). Using deionized water as a working fluid, two different flow rates (100 and 200 ml/min) were evaluated at a constant inlet subcooling of 30 K. The heatsinks were combined with jet-impingement technology and a tip clearance of 50 μm. An innovative local thermohydraulic assessment was obtained due to the introduction of seven thermocouples within one half of the symmetric heatsink, providing an accurate analysis. Results indicated that the PF sample achieved peak heat transfer values of 7318 W/°C·m 2 at 100 ml/min (24.7 W/cm 2 ) and 10,982 W/°C·m 2 at 200 ml/min (38.65 W/cm 2 ). For the S-SVW-Mchs, peak values were 6438 W/°C·m 2 (22.72 W/cm 2 ) and 15,541 W/°C·m 2 (44.46 W/cm 2 ). Nucleation occurred at lower wall superheats in PF (0.54–4.27 °C) than in S-SVW-Mchs (3.54–18.10 °C). In addition, PF reached higher critical heat flux levels: 32.31 vs 26.38 W/cm 2 (+23% of enhancement) and 58.11 vs 50.23 W/cm 2 (+16%). The microchannel sample showed higher pressure drop and more severe flow boiling instabilities than pin-fins. A boiling utilization (Bu) benchmark was carried out against the literature, confirming that this cooling device design is a promising flow boiling cooling approach.