Levitating droplets of liquid condensate are known to organize themselves into ordered arrays over hot liquid-gas interfaces. The mechanism of levitation is the Stokes force acting onto a drop from the flow originated at the interface. We report experimental observation of levitation and self-organization of liquid microdroplets (with size on the order of 10 µm) over both hot liquid-gas interfaces and heated dry solid surfaces. In the experiment a copper block heated from below is used as the substrate. Degassed ultra-pure water is used as the working liquid. Optical recording is made using a high-speed camera equipped with a microscope objective of high resolving power. Working liquid is deposited with a syringe onto the substrate to form a horizontal liquid layer. The heater is then switched on, resulting in evaporation and formation of droplet array levitating over liquid surface. With a short pulse of air jet a dry spot is formed on the copper surface. When the array moves to the dry spot, the droplets continue to levitate over the solid dry surface. Even though the life-time of the array is shorter over the dry surface, its geometric characteristics are remarkably similar to the case of levitation over liquid-gas interface. Mathematical models are developed that explain droplet levitation for both configurations and lead to new power laws for the levitation height as a function of droplet size. The predictions of the models are in good quantitative agreement with the experimental data. Using the insights from the models and new experiments, we are able to resolve some long-standing controversies from previous studies of levitating liquid droplets.
|Журнал||International Heat Transfer Conference|
|Состояние||Опубликовано - 1 янв. 2018|
|Событие||16th International Heat Transfer Conference, IHTC 2018 - Beijing, Китай|
Продолжительность: 10 авг. 2018 → 15 авг. 2018