Thermal Circuit Analysis of Droplet Evaporation on Hot Microstructured Superhydrophobic Surfaces

Abstract

In this paper, the evaporation dynamics of solitary water droplet dwelling on the hot micro-structured superhydrophobic surfaces is experimentally and theoretically investigated. For the first time, two distinguished components of heat and mass transfer, i.e., from the droplet cap and the base surface, during the droplet evaporation are systematically studied. Considering all the thermal resistances from the heated substrate to the droplet cap surface, a comprehensive thermal circuit model is developed to analyze the effects of micropillars and substrate temperature on the sessile droplet evaporation. As substrate temperature increases, a more apparent temperature mismatch between droplet cap surface and heated substrate is experimentally observed, which could be explained by the increasing droplet cap surface evaporation rate and its evaporative cooling effect. Moreover, the increasing temperature of droplet cap during the evaporation could be successfully predicted by our model, indicating the component of evaporation ratio from the droplet base surface (φ) decreases. This work could advance our understanding of droplet evaporation on heated superhydrophobic surfaces and further provide us a new tool to accurately predict droplet temperature and evaporation rate during the evaporation process.