Enhancing dry-out heat flux on nano-SiO2 porous surfaces

Abstract

In this study, we investigated the heat transfer behavior of droplet evaporation on a heated surface. Hydrophilic surfaces were coated with SiO2 nanoparticles using the sol-gel method. The droplet evaporation process on the heated surface was captured using a high-speed camera. We found that there is a critical value of the liquid film thickness that leads to a higher heat flux at the end of the droplet evaporation process (dry-out). This critical value is known as the dry-out heat flux. The thickness of the liquid film only reached the thin-film region of the evaporation meniscus theory at the end of the evaporation, resulting in strong evaporation and high heat flux. In this study, we observed that the surface exhibited hydrophilic wettability due to the nano-SiO2 porous structure. The dry-out heat flux can be further improved by approximately 30 % at 90 °C on the heated surface. This improvement is attributed to the higher capillary force of the nano-SiO2 porous structure, which increases the interfacial area. Additionally, surfaces heated to the same temperature develop a thinner liquid film, thereby achieving a higher heat flux. This investigation provides guidelines for applications in printing, heat exchangers, and microfluidics.