Molecular dynamics simulation of the roles of roughness ratio and surface potential energy in explosive boiling

Abstract

Nanostructure can apparently affect explosive boiling through surface roughness that functions as a cavity for activating the bubble nucleus. In this work, the effect of surface roughness on the explosive boiling of water film over the copper surfaces with nanochannels having different heights and spacing is investigated. It is found that the increase in the roughness ratio by raising the channel height can substantially promote the onset time of boiling, increase the temperature and heat flux of water, and reduce the interfacial thermal resistance. The increase in roughness ratio by reducing the channel spacing has a promotion effect first and then a weakening effect on the boiling heat transfer. A critical channel spacing is proposed to address this effect on boiling heat transfer on surfaces with increasing roughness ratio by reducing the channel spacing. Moreover, a two-dimensional surface potential energy is used to address the relationship among the roughness ratio, interaction potential energy, and explosive boiling characteristics of the liquid molecules on the structured surfaces. The absolute value of surface potential energy increases with increasing roughness ratio with an increase average rate of 7.1 eV. It is concluded that, when the channel spacing exceeds the critical value, the major reason for the enhanced heat transfer by increasing the roughness ratio is essentially the improvement of the surface potential energy by increasing the heat transfer area. Further investigations on nanochannels with different heights and spacing indicate that the critical channel spacing of 1.444 nm is also suitable for more nanochannel surfaces. The findings of this study can help for a better understanding of the mechanisms of explosive boiling of various fluids on nanostructured surfaces by the surface potential energy.