Levitating droplets of liquid condensate are known to organize themselves into ordered arrays over hot liquid-gas interfaces. Themechanism of levitation is the Stokes drag force acting on a drop from the flow originated at the interface. We report experimental observation of levitation and self-organization of liquid microdroplets (with a 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 ultrapure water is used as the working liquid. An 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 ordered droplet array levitating over a liquid surface. With a short pulse of an 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 lifetime of the array is shorter over the dry surface, its geometric characteristics are similar. 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 agreement with the experimental data.
|Журнал||Interfacial Phenomena and Heat Transfer|
|Состояние||Опубликовано - 1 янв 2018|