Effects of wettability and heat flux on water nanofilm phase change over copper plate

Microscopic boiling heat transfer has received much research interest because of its performance-enhancing qualities and other potential applications in the field of micro- and nanotechnologies. In this study, the phase change of a water nanofilm over smooth copper plates under different wetting and heat flux conditions is investigated via molecular dynamics simulations. Results show that the plate at higher heat flux experiences a faster rise in temperature, which enhances both normal evaporation and explosive boiling. In addition, simulations under the same heat flux show that a hydrophobic surface exhibits a faster temperature rise owing to its higher Kapitza resistance compared with a hydrophilic surface, which leads to an earlier onset of explosive boiling. Results for the normal evaporation show that the entire liquid film is heated to a uniform temperature well above its boiling point, and this temperature is almost independent of surface wettability under the same heat flux. Moreover, the critical heat flux increases along with surface hydrophilicity. These phase change behaviors and the insights into the mechanisms presented in this study may contribute to the fundamental understanding and application of nanofilm boiling heat transfer.