Evaporation characteristics of sessile droplets on flat hydrophobic surfaces in non-boiling regime

Abstract

The evaporation of the sessile droplets is a frequent and complicated interfacial movement phenomenon that is broadly used in engineering technologies such as spray cooling. The investigation of the droplet evaporation on hydrophobic surfaces is of great significance for passively enhancing heat and mass transfer. In this paper, the evaporative traits of sessile droplets on a hydrophobic surface in non-boiling regime at constant temperature were examined. The deionized droplets volume ranged from 0.5 μL to 4.0 μL, and the surface temperature ranged from 30 °C to 70 °C. The variation law of the parameters including contact angle, contact line and droplet lifetime during the droplet evaporation process was investigated. The results demonstrate that the droplet evaporation time is positively correlated with the initial volume and the surface hydrophobicity, but negatively correlated with the surface temperature during droplet evaporation on the hydrophobic surface. The change mode of contact angle is significantly affected by the initial volume and the surface temperature, and the contact diameter is significantly affected by surface temperature. As the surface temperature and the droplet volume increases, the variation mode of contact angle is abundant. Evaporation of sessile droplets on superhydrophobic surface is more prone to contact line slip phenomenon than that on hydrophobic surface, which restrains the droplets evaporation to a certain extent. The evaporation of droplets on (super)hydrophobic surfaces also follows the V2/3 law.