Josh Tulkoff constructs a large prototype of the fog harp, which consists of a vertical array of 700 wires and is based on initial experimental results. Tulkoff was part of an interdisciplinary research team at Virginia Tech that discovered parallel wire arrays could increase the water collection capacity of fog nets by threefold.

Fog harvesting may look like whimsical work.

After all, installing giant nets along hillsides and mountaintops to catch water out of thin air sounds more like folly than science. However, the practice has become an important avenue to clean water for many who live in arid and semi-arid climates around the world. 

A passive, durable, and effective method of water collection, fog harvesting consists of catching the microscopic droplets of water suspended in the wind that make up fog. Fog harvesting is possible – and has gained traction over the last several decades – in areas of Africa, South America, Asia, the Middle East, and even California. As illustrated by recent headlines of South Africa's countdown to "Day Zero," or the day the water taps are expected to run dry, water scarcity continues to be a growing problem across the globe. Leading researchers now estimate that two-thirds of the world's population already live under conditions of severe water scarcity at least one month of the year.

Fog harvesting could help alleviate that shortage, and now an interdisciplinary research team at Virginia Tech has improved the traditional design of fog nets to increase their collection capacity by threefold.

Published in ACS Applied Materials & Interfaces and partially funded by the Virginia Tech Institute for Creativity, Arts, and Technology, the team's research demonstrates how a vertical array of parallel wires may change the forecast for fog harvesters. In a design the researchers have dubbed the "fog harp," these vertical wires shed tiny water droplets faster and more efficiently than the traditional mesh netting used in fog nets today.

"From a design point of view, I've always found it somewhat magical that you can essentially use something that looks like screen door mesh to translate fog into drinking water," said Brook Kennedy, associate professor of industrial design in the College of Architecture and Urban Studies and one of the study's co-authors. "But these parallel wire arrays are really the fog harp's special ingredient."

To test the fog harp’s design, researchers constructed small-scale models of vertical wire arrays that could be placed inside an environmental chamber with artificial fog. The team discovered that water collection efficiency continued to increase with smaller and smaller wires.

Fog nets have been in use since the 1980s and can yield clean water in any area that experiences frequent, moving fog. As wind moves the fog's microscopic water droplets through the nets, some get caught on the net's suspended wires. These droplets gather and merge until they have enough weight to travel down the nets and settle into collection troughs below. In some of the largest fog harvesting projects, these nets collect an average of 6,000 liters of water each day.

However, the traditional mesh design of fog nets has long posed a dual constraint problem for scientists and engineers. If the holes in the mesh are too large, water droplets pass through without catching on the net's wires. If the mesh is too fine, the nets catch more water, but the water droplets clog up the mesh without running down into the trough and wind no longer moves through the nets.

SOURCE VIRGINIA TECH

Taxonomy

• Water from Air