Enhancing pool boiling heat transfer performance via deposition of nanoparticles with different sizes on micropillar surfaces

Boiling heat transfer is attracting attention for next-generation cooling systems due to its superior heat transfer efficiency. In this study, we investigated the effects of nanoparticle-deposited micropillar structures (NMPSs) with different nanoparticle sizes on the heat transfer coefficient (HTC) and critical heat flux (CHF) of the heating surfaces. Improvements were observed in both CHF and HTC, which could be explained by the wicking, porosity, and bubble departure characteristics. The micropillars had a 4 μm diameter and 10 μm gap, while the nanoparticles had sizes of 8, 60, and 400 nm. Only the 400 nm NMPS achieved an enhancement in CHF and HTC value relative to the bare micropillar structure, with respective improvement margins of 13 % and 17 %. The existing correlation between CHF and wicking characteristics could not explain the wicking experiment result. Therefore, a new CHF correlation that simultaneously considers both wicking and porosity was suggested. Predictions based on the proposed correlation were highly accurate for experimentally measured CHF values, with an error margin of only ±5 %. In conclusion, the findings highlight that larger nanoparticles (i.e., 400 nm) yield greater improvements in CHF and HTC by enhancing the wicking ability and porosity of surfaces with highly porous micro/nano-composite structures.