Research on Evaporation and Deposition Characteristics of Suspended Droplets Containing Nanoparticles

Evaporation of functional nanoparticle-containing droplets on solid surfaces plays a key role in applications such as air conditioning, refrigeration, and electronic cooling. In this study, we experimentally investigated the evaporation behavior and particle deposition of nanofluid droplets on solid surfaces. The deposition patterns were photographed, and microscopic characterizations were performed. The results show that the droplets always evaporate in the mode of constant contact radius. Changes in substrate temperature and droplet volume have little influence on the evaporation mode and morphology of the droplets, and the contact angle changes linearly with time. The surfactant can significantly regulate the kinetic behavior of droplet spreading. The addition of only 0.25% of surfactant sodium dodecyl sulfate (SDS) increases the droplet spreading radius from 0.71 mm to 1.12 mm, decreases the initial contact angle from 83° to 54°, and increases the area of spreading by 89%. The substrate temperature and droplet volume significantly affect the deposition patterns after droplet evaporation. The higher the substrate temperature, the larger the droplet volume and the more obvious the coffee-ring pattern formed after evaporation. SDS significantly increases the coffee ring width, which reaches 230 μm when the mass fraction of SDS reaches 1.00%, and the particles have been widely distributed throughout the entire evaporation area, suggesting that the coffee ring effect has been effectively suppressed. By introducing the Ma number, the influence of the Marangoni effect, guided by temperature, volume, and mass fraction changes, on the internal flow of droplets and the mechanism of coffee-ring formation are explained.