MIT engineers have developed a new, inexpensive water recovery system to capture water droplets from plumes of industrial cooling towers.
The system works in the following manner: When air that’s rich in fog is zapped with a beam of electrically charged particles known as ions, water droplets become electrically charged and thus can be drawn toward a mesh of wires placed in their path.
The droplets then collect on that mesh, drain down into a collecting pan, and can be reused in the power plant or sent to a city’s water supply system.
The system is the basis for a startup company called ‘Infinite Cooling,’ co-founded by PhD holder Maher Damak and associate professor Kripa Varanasi.
Most recovery systems consist of some kind of plastic or metal mesh hung vertically in the path of fogbanks, making them extremely inefficient, as they capture only about 1 to 3 percent of the water droplets passing through them.
The reason for this inefficiency is due to the aerodynamics of the system, contends Damak and Varanasi.
For instance, when a stream of air passes an obstacle, such as the wires in these mesh fog-catching screens, the airflow naturally deviates around the obstacle, much as air flowing around an airplane wing separates into streams that pass above and below the wing structure.
These deviating airstreams carry droplets that were heading toward the wire off to the side, unless they were headed bang-on toward the wire’s center.
The end result is that the fraction of droplets captured is far lower than the fraction of the collection area occupied by the wires, because droplets are being swept aside from wires that lie in front of them.
The MIT team is presently focusing on capturing water from the plumes of power plant cooling towers as their stream of water vapor is much more concentrated than any naturally occurring fog.
And since capturing evaporated water is in itself a distillation process, the water captured is pure – even if it was previously found to be salty or contaminated.
Varanasi opines that a 600-megawatt power plant could capture 150 million gallons of water a year, representing a value of millions of dollars.
Moreover, since a majority of power plants are placed along arid coastlines, this could pave way for simpler water desalination services.
“This can be a great solution to address the global water crisis,” says Varanasi. “It could offset the need for about 70 percent of new desalination plant installations in the next decade.”
Image, video and content copyrights: Christine Daniloff/Melanie Gonick/MIT