Effect of loaded carbon-based nanoparticles on the evaporation dynamics of sessile droplets

Droplet evaporation is an essential physical process in industrial fields such as spray cooling and inkjet printing. With the widespread use of carbon materials, carbon-based nanofluid droplets have great potential to improve the efficiency and quality of applications in these fields. Therefore, understanding the effects of materials and external factors on the carbon-based nanofluid droplets evaporation dynamics becomes crucial. In this experimental study, the nanofluid droplets were prepared based on two common carbon-based nanomaterials, multi-walled carbon nanotubes (MWCNTs) and multi-layer graphene (MLG). The monocrystalline silicon wafer is used as the substrate, and the substrate temperature is controlled between 50 °C and 80 °C. Using the DI water droplets as a comparison, the effects of loading different carbon-based nanoparticles on wettability, evaporation modes, and heat transfer processes at the liquid-vapour interface were explored. The experimental results show that droplets loaded with MLG nanoparticles and sodium dodecyl sulfate (SDS) have the best evaporation efficiency, which can be improved by up to about 2.1 times compared with DI water. Furthermore, compared with the variable evaporation mode of the DI water droplets, the evaporation process of MLG nanofluid droplets is dominated by constant contact radius mode. At the same time, compared with DI water and MWCNTs, loaded MLG can reduce the liquid-vapour interface temperature difference by up to 3.7 °C and 1.0 °C, respectively, which effectively suppresses the evaporative cooling effect. Besides, the experimental results about the sedimentary pattern showed that MWCNTs can suppress the coffee-ring effect more effectively than MLG. Under various conditions, MLG nanoparticles can make the sedimentary pattern have greater surface roughness, which is about 1.8 times higher on average compared with MWCNTs.