Effects of liquid film thickness and surface roughness ratio on rapid boiling of water over copper plates

Abstract

This work investigated the effect of liquid film thickness and surface roughness ratio on the rapid boiling of water over the copper plates in terms of hydraulic diameter defined based on the overall cross-sectional area available for the flow of water film. It is found that the reduction of the hydraulic diameter by increasing the surface roughness ratio can substantially promote the performance of rapid boiling, because of the increase in heat transfer area, together with a decrease in the Kapitza resistance. As a combined effect of the film thickness and the Wenzel roughness ratio, the hydraulic diameter can determine the onset time of boiling and the equilibrium temperature, while it can also determine the heat transfer rate and the Kapitza resistance if the film thickness or the surface roughness is fixed. The effects of the hydraulic diameter on the performances of nanoscale boiling can be applied for heat transfer enhancement and process intensification over any structure in phase-change devices and chemical equipments.