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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Influence of Dynamic Wettability on Evaporation Kinetics of Microscopic Sessile Droplets

Get access (open in a dialog) DOI: 10.1615/IHTC15.evp.009732
pages 2339-2348

Sinopsis

The kinetics of evaporating water droplets on smooth substrates was experimentally investigated using an automatic microscopic contact angle meter. The use of nanoliter droplets minimized the influence of gravity and conduction resistance on the rate of evaporation, allowing acquisition of high quality droplet shape evolution data. The droplets were observed to first evaporate in the contact line pinning mode followed by the constant receding contact angle mode until complete evaporation to the ambient. The experimentally determined rate of evaporation was found to be a strong function of the dynamic wettability of the droplets. Sessile droplet models reported in literature were not able to accurately predict the evolution of contact angle and the size of the evaporating droplets in our experiments. We attribute this discrepancy to the fact that most of the models in literature were either valid for only contact line pining mode or constant receding contact angle mode, while the droplets in our experiments evaporated sequentially in both modes. Accordingly, we used the physical insights obtained from the high-resolution microscopic contact angle measurements to develop a unified model for predicting the rate of evaporation for these droplets. The prediction results showed good agreement with the experimentally evolving contact angle, droplet base radius, and height in both the contact line pinning mode as well as the constant receding contact angle mode. The model was further validated by predicting the evaporation rate of high contact angle and minimal hysteresis droplets on superhydrophobic surfaces. This study offers new insights, extending the fundamental understanding of solid-liquid interactions required, for the design of functional coatings for advanced heat transfer applications.