Effect of nanocavity geometry on nanoscale nucleate boiling heat transfer

Abstract

In recent years, surfaces with nanocavities have been identified to considerably improve boiling heat transfer, that is highly promising for advanced thermal energy systems. To boost developments in nanostructured boiling surfaces, effects of nanocavity geometry on nucleate boiling at the nanoscale are systematically studied for the first time by utilizing molecular dynamics simulation. Three typical nanocavities with rectangular, semicircular, and triangular cross-sectional shapes are constructed, which have the identical width and depth (8 nm and 4 nm). Moreover, three representative wetting conditions corresponding to different solid-liquid interaction strengths are further considered to provide a comprehensive understanding of geometry effects. The results manifest that nanocavity geometry effect on nucleate boiling can be attributed to the differences in their solid-liquid contact area and solid-liquid interactions play a vital role in reinforcement effectiveness. When the solid-liquid interaction is sufficiently strong (energy coefficient equals 1.5, termed ultra-superhydrophilicity), variations in nanocavity geometries will induce remarkable effects on boiling performance. Among three geometric configurations, the rectangular nanocavity exhibits the highest heat transfer efficiency and achieves maximum boiling enhancement, including significant improvements in bubble nucleation and growth, as well as critical heat flux. This study provides an essential insight into nanoscale boiling reinforcement mechanism.