Christmas Color Drops Hint at Fog Gathering Solutions

When two water droplets merge into a tilted superhydrophilic wire, their movement speed increases.

They also create something visually impressive.

New research from Northwestern Engineering’s Kyoo-Chul Kenneth Park reports how beautiful necklace-shaped droplets in a fiber propel themselves along their fusion—increasing its speed by up to 270 percent of its pre-coalescing speed. The findings could help researchers optimize many environmental processes, such as mist collection, mist removal, filtration, oil/water separation, and microplastic collection.

Park, an assistant professor of mechanical engineering at the McCormick School of Engineering, presented his work in the article “Coalescing-Induced Droplet Propulsion in a Superhydrophilic Wire,” published December 5 as the cover story of the latest issue of Letters of Applied Physics.

Park tested different droplet sizes and viscosities on wires with various diameters, looking for the optimal combination of speed and energy. When he found the correct ratio, he discovered that their joint speed increased almost three times.

“The bulk droplet velocity increase is due to the two-wedge velocity difference of the fused droplet in damped oscillation following coalescence, driven primarily by the transition from surface to kinetic energy,” said Park, whose interests Research interests include multi-length scaling surface fabrication, thermal fluid engineering, and bio-inspired surface engineering for a sustainable future.

By better understanding droplet transport in a cylindrical wire, Park is one step closer to optimizing a key area of ​​his research: fog collection. What lack of water Growing as a global challenge, mist collectors (sheets of hydrophilic mesh stretched on two vertically aligned poles) have emerged as an affordable and accessible way to collect water from the air. However, they are inefficient, with water droplets it often leaks through the mesh if the wires are the wrong size.

“This work could provide the theoretical foundation for a new way to design 3D fog collectors that outperform conventional 2D meshes,” Park said.

Another potential use is in the development of medicine; more specifically, new methods of biomedical filters.

“The new phenomenon and mechanism on the sudden increase of droplet velocity along a superhydrophilic wire will benefit several fields, including biomedical research That requires rapid transport of liquids, such as masks and filters to protect people from airborne microplastics and virus-containing droplets,” Park said.

Building on this work, Park and his research team will investigate other applications, such as mist removal and the collection of droplets containing microplastics.