Electrostatic forces influence the distribution of drops in turbulent channel flows

Electric fields are used to control emulsions of liquid drops in several industries. In the offshore oil industries, electrocoalescence, where droplets coalesce under the influence of electric fields, plays an important role in separating the emulsions of oil and water after passing through pipelines. Electrocoalescence has been found to be more complex in turbulent flows, and the effect of electrostatic fields under these conditions is not deeply understood.

Lu et al used numerical simulations to examine how electric fields affect the drop distribution in turbulent channel flows.

“We found that the distribution of drops varies with electric intensity,” said author Ying Zhang. “All the drops in the channel tend to line up and form columns spanning the channel width when the electric force is strong enough.”

The team’s experiments were conducted under the leaky dielectric model, which shows that drop shape is determined by viscous and electric stresses.

“Leaky dielectric drops can be found in nature, such as in milk, petroleum and crude oil,” said Zhang. “It is very important to find out the rheological properties of those drops in electric field, so we can recover and purify products.”

The study concludes, in fields of low electric intensity, drops will be driven to the walls of the flow channel, while in high intensity electric fields, drops aggregate into long columns. The researchers used relatively large drops for their study, so whether the same holds true for small drops in turbulent flow channels remains to be seen.

Source: “Effect of electrostatic forces on the distribution of drops in turbulent channel flows,” by Min Lu, Jiacai Lu, Ying Zhang, and Grétar Tryggvason, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5119925 .