Study of drop impact on thin fibers helps with net design for water collection

When a droplet of rain falls onto a spider’s web, there are a few predictable outcomes: If the drop falls fast, it may pass through the web and might even split into two smaller droplets. If the drop falls slowly, it could be captured by the web. Though this is an example of the phenomena at work in nature, the dynamics of drop impact on a thin fiber is of interest to researchers for its potential application in water collection.

Zhu et al. detailed the dynamics of drop on fiber collision and examined a variety of factors that affect possible outcomes. They found drop splitting, which causes the drop to pass through the fiber instead of being collected, happens not only at high speeds, but at low speeds too. The studies also revealed that impact velocity, drop oscillation and fiber wettability all play a contributing role in whether a droplet bounces off, rolls over or splits on a fiber.

“In arid regions, water means life. Our study can help to optimize the structural parameters of the netted water collectors for harvesting fog,” said author Jun Zou. “Depending on the fog drop diameter and the wind speed, fibers of different diameters, materials and initial tensions should be used.”

Using a high-speed camera, the team observed water falling from a syringe onto a tightly-strung nylon fiber and saw that low-speed splitting – previously unrepresented in any studies – vanished with the use of hydrophilic material.

“As we hope this study can help the design of netted water collectors, further research should focus on the net structure,” said Zou. “Intersections of the crossed fibers on the net can capture more water than the single fiber.”

Source: “Experimental study of drop impact on a thin fiber,” by Pingan Zhu, Wei Wang, Xiang Chen, Fangye Lin, Xiaofeng Wei, Chen Ji, and Jun Zou, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5116845 .