>Architecture, Design, Engineering

Fog Harp

Fog Harp aims to develop a full scale model to test a promising, potentially revolutionary fog collecting technology. Inspired by natural processes and modeled specifically on the way in which mighty Sequoia trees collect water from coastal fog, known as fog drip, Fog Harp has the potential to address water scarcity problems in some of the poorest and driest countries on Earth. Incorporating vertical wires into the preexisting “screen mesh” design, Fog Harp plans to increase the efficiency of these nets so that they may be adapted to first world applications particularly on the California coast.

The Earth is 70 percent water, but almost all of that liquid is seawater us humans can’t drink. Already, California is besieged by drought, while citizens in South Africa’s Cape Town try to push back Day Zero, the day the city runs out of water. As our population grows and temperatures rise, the global water crisis worsens, spurring scientists to develop better ways of harvesting water.

Around the world, people living on coasts collect water by harvesting the fog. “Fog is a cloud very low on the ground,” explains Jonathan Boreyko, an engineer at Virginia Polytechnic Institute and State University who studies nature-inspired fluids. Fog harvesters are mesh nets, usually one meter squared, erected perpendicular to the path of the wind. As the wind blows fog through the device, the mesh catches the droplets, and gravity pulls the water down into containers underneath. Most of the time, fog harvesters collect about three liters a day per square meter of mesh.

In some of the most arid regions of the world, from the Sahara to the Andes, special nets have long been used to catch moisture from the air, turning fog into drinking water.

These fog harvesters are put up against wind streams to catch microscopic droplets which gather and merge on a fine mesh until they have enough weight to travel down into a water tank. They provide essential access to water to many communities, and the technology behind them has evolved over the years to offer a higher yield, resistance to the elements and a reduced need for maintenance.

Now, researchers at Virginia Tech University have developed a new design that they say has three times the efficiency of regular fog nets. They call it a "harp," because its vertical pattern of wires makes it resemble the string instrument.

Harvesting water from fog isn’t just a chore for young Luke Skywalker — it’s become an important part of bringing clean water to people living in drought-prone climates across the globe. The problem is that harvesting tools can be pretty inefficient.

Now, engineers from Virginia Tech have designed a device that may be able to extract three times as much water from fog as previous tools. They’re calling the device the “fog harp” because the secret is in the way its array of parallel wires lines up like the strings of the instrument.

Most fog harvesters used today are massive nets that capture water droplets blown in by the wind. The droplets merge on the net and then stream down to a collection container at the bottom. If the net’s holes are too large, the droplets sneak through. If they’re too small, the holes can get clogged.

Fog harvesting is a useful technique for obtaining fresh water in arid climates. The wire meshes currently utilized for fog harvesting suffer from dual constraints: coarse meshes cannot efficiently capture microscopic fog droplets, whereas fine meshes suffer from clogging issues. Here, we design and fabricate fog harvesters comprising an array of vertical wires, which we call “fog harps”. Under controlled laboratory conditions, the fog-harvesting rates for fog harps with three different wire diameters were compared to conventional meshes of equivalent dimensions. As expected for the mesh structures, the mid-sized wires exhibited the largest fog collection rate, with a drop-off in performance for the fine or coarse meshes. In contrast, the fog-harvesting rate continually increased with decreasing wire diameter for the fog harps due to efficient droplet shedding that prevented clogging. This resulted in a 3-fold enhancement in the fog-harvesting rate for the harp design compared to an equivalent mesh.

BLACKSBURG,Va. (WDBJ7) The answer to fixing a water shortage could be floating through the air. Researchers at Virginia Tech are pulling water from fog using a harp. You can't play a tune with the fog harp, but it's music to people's ears who have been looking for a solution to a global water shortage crisis. The concept is nothing new. Researchers have designed ways of pulling water from what seems like thin air to drink for while, but a team here at Virginia Tech noticed a flaw in the design. "Currently fog harvesters are comprised of this kind of mesh netting. And the problem that we have with this design is you have this duel constraint. Where if the wires are too close together the water actually clogs inside of the holes and gets stuck," said Jonathan Boreyko, an assistant professor in the Department of Biomedical Engineering and Mechanics Researchers in Blacksburg developed a harp, not for entertainment, rather to harvest a necessity. "With this design, which is composed of vertical wire array that clogging doesn't happen and water droplets are more free to drop away," said Brook Kennedy, an industrial design professor. It works like this, seen here in this demonstration. Fog passes through the harp, water droplets quickly build on the wires and pour into a container where it's collected and can be used for drinking water and irrigation.

Virginia Tech ‘fog harp’ increases collection capacity for clean water

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.

Brook Kennedy, Industrial Design
Dr. Jonathan Boreyko, Biomedical Engineering & Mechanics

Collaborative Colleges:
Architecture & Urban Studies