Harvesting fog could bring water to millions
Harvesting fog could bring water to millions
Friday, March 14, 2014 - 12:00
In northern Chile, as in many other parts of the world, freshwater is a limited commodity, but heavy fogs are a regular occurrence. For at least two decades, people in such areas have turned to fine mesh nets to harvest moisture from fog, but to date the nets have never been terribly efficient. Now, new research could greatly improve the nets’ efficiency, increasing the amount of water they’re able to capture.
Predominantly made of plastic fibers and usually placed on hillsides, fog collectors look something like volleyball nets with a much tighter weave. Droplets run down the mesh into a trough or bucket, where the water can be collected for drinking by people or livestock, or for irrigation.
Current meshes collect about 2 percent of the moisture that passes through them, says Gareth McKinley, a mechanical engineer at MIT. Hoping to improve the meshes, McKinley and MIT chemical engineer Robert E. Cohen reimagined mesh technology, starting with computer models and working up to field-ready prototypes that are about five times more efficient at harvesting fog. “For realistic wind speeds, realistic droplet sizes and realistic materials, that’s close to the maximum [efficiency] you could hope to achieve with a simple engineering design,” McKinley says.
The team began by optimizing the size of the fibers and the holes between them in the mesh. Commonly used meshes have holes about five millimeters apart, a little smaller than the width of a pencil. McKinley and Cohen’s team, however, found that meshes looking more like window screens are better, with filaments just 200 to 300 micrometers in thickness, or about two or three times thicker than an average human hair, and spaced apart twice that width. They also changed materials, opting for stainless steel over polyolefin, an inexpensive plastic. These improvements let the mesh collectors catch more water and also made them more resistant to damage, the team reported in the journal Langmuir.
More:
http://www.earthmagazine.org/article/harvesting-fog-could-bring-water-millions
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