Evaporation of ultra-thin water film on hot spot with nanopillar array

For the ultra-thin film evaporation, a hot spot was formed by a local dry out, resulting in the heat transfer deterioration. In this work, the stable evaporation of ultra-thin water film on hot spot with designed nanopillar structure was studied based on the non-equilibrium molecular dynamics (MD) simulation. The variation of molecular motion trajectories, evaporation rate and number of migrating water molecules in different regions were recorded over time in the simulation. The results show that the nanopillar array on the hot spot can attract the surrounding liquid to wet the overheated region due to the strong solid-liquid interaction, both the evaporation stability and heat transfer performance can be improved. By comparing three surfaces with different nanopillar arrays on hot spot, it shows that the evaporation rate is one important factor affecting the amount of liquid replenishment: with the increasing number of nanopillars, both the evaporation performance and liquid replenishment capacity are improved. Moreover, the effect of two designed nanostructure configurations on the evaporation performance was investigated. Compared to the configuration of only nanopillar array on the hot spot, the configuration of nanopillar array on the whole surface has a lower temperature for the nanopillars and delays the occurrence of dry out, while the averaged evaporation rate may be reduced as well. Therefore, there is a trade-off between the surface temperature reduction and evaporation rate enhancement. The findings in this study can provide a guidance for the thermal design for the hot spot in the chip cooling technique under the high heat flux application. • Nanopillar array can attract the surrounding liquid to replenish the hot spot. • Evaporation and replenishment are improved with increasing nanopillars on hot spot. • Nanopillar array on whole surface delays the occurrence of dry out phenomenon. • A trade-off between temperature level and evaporation rate is proposed.