Wetting dynamics and heat transfer of droplet evaporation around boiling point: Facile manipulation by surface roughness

Abstract

The evaporation of water–ethanol droplets on solid surfaces has vast potential for applications in thermal management, microfluidics, and biomedical sciences, while the approach of manipulating wetting dynamics and heat transfer of droplet evaporation around the boiling point remains open for investigations. The present study proposes a facile approach: fabricating solid surfaces with diverse roughness by sandpaper milling with different grit densities, which can alter the wetting and heat transfer characteristics of droplet evaporation. We discover that when the temperature of the heated surface exceeds the droplet boiling point, the existence of bubbles affects the solid–liquid wetting state; surface roughness alters the ability of bubble departure, thus determining the solid–liquid contact and the contact line retraction time. Consequently, in this case, the solid–liquid contact area and the heat absorbed from heated surfaces for droplets changes with surface roughness, altering the droplet evaporation time and the average heat flux at the solid–liquid interface. Bridged by droplet wetting dynamics, the heat transfer of droplet evaporation above the boiling point can be manipulated by adjusting surface roughness, offering a facile approach to tuning the process of droplet evaporation in the related industrial applications.