Category: electrohydrodynamics

This polygonal pattern is known as the rose-window instability….

This polygonal pattern is known as the rose-window instability. It’s formed between two electrodes – one a needle-like point, the other flat – separated by a layer of oil. The pointed electrode’s voltage ionizes the air nearby, creating a stream of ions that travel toward the flat electrode below. Oil is a poor conductor, however, so the ions build up on its surface until they’re concentrated enough to form a dimple that lets them reach the lower electrode. At higher voltages, the electrical forces driving the ions and the gravitational force trying to flatten the oil reach a balance in the form of the polygonal cell pattern seen above. Smaller cells form near the needle electrode, where the electrical field is strongest and the temperature is highest, as revealed in thermal and schlieren imaging (lower images) that shows a warm stream of gas impacting there. 

As a final note, I’ll add that the latest in this research comes from a paper by a Pakastani teenager. It’s never too early to start contributing to research! (Image and research credit: M. Niazi; via NYTimes; submitted by Kam-Yung Soh)

Posted in electrical field, electrohydrodynamics, fluid dynamics, instability, physics, rose window instability, sciblr, science

Here you see a millimeter-sized droplet suspended in a fluid…

Here you see a millimeter-sized droplet suspended in a fluid that is more electrically conductive than it. When exposed to a high DC electric field, the suspended drop begins to flatten. A thin rim of fluid extends from the drop’s midplane in an instability called “equatorial streaming”. As seen in the close-up animation, the rim breaks off the droplet into rings, which are themselves broken into micrometer-sized droplets thanks to surface tension. The result is that the original droplet is torn into a cloud of droplets a factor of a thousand smaller. This technique could be great for generating emulsions of immiscible liquids–think vinaigrette dressing but with less shaking! (Image credit: Q. Brosseau and P. Vlahovska, source)

Posted in electrical field, electrohydrodynamics, emulsion, fluid dynamics, instability, miscibility, physics, sciblr, science, surface tension