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Today, 39% of all the fresh water
taken from rivers, lakes, and reservoirs in the
United States is earmarked for the cooling needs
of power plants that use fossil fuels
or nuclear power.
The problem?
A large portion of that water ends up floating away
in clouds of vapor.
In other words, hundreds of billions of gallons
of clean, otherwise usable water are lost each year.
But now, a new system devised by a team of MIT engineers
could provide an efficient, low-cost way
to capture a substantial amount of that lost water,
ultimately making power plants less wasteful
and more self sustaining.
And the water collected could become a source
of potable water for parched cities around the world.
The motivation to develop this new system
stems directly from the inefficiencies
of current natural fog harvesting systems.
Existing systems, which generally consist of
a plastic or wire mesh hung vertically in the path
of fog banks, only capture about one to three percent
of the water droplets that pass through them.
The reason for such a tiny percentage is the result
of aerodynamics.
As a stream of air passes an obstacle,
such as the wires in these mesh fog catching screens,
the air flow naturally deviates around the obstacle.
Thus, carrying droplets that were heading toward the wire
off to the side.
The researchers found once they zap the fog
with a beam of electrically charged particles
known as ions, the opposite effect happens.
Not only do all the droplets that are in the path
of the wires land on them, but even droplets
that were aiming for the holes in the mesh
get pulled toward the wires due to the charge.
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 team is currently building a full-scale
test version of their system,
to be placed on the cooling tower of MIT's
central utility plant—
a natural gas co-generation power plant
that provides most of the campus's electricity,
heating, and cooling.
In a series of experiments, the researchers demonstrated
the concept by building a small lab version
of a stack emitting a plume of water droplets.
They then placed their ion beam and mesh screen on it.
When the condenser is off, a thick plume of fog droplets
rise from the device.
Once the condenser is turned on, the plume
almost instantly disappears and liquid can be seen
condensing on the wire dome.
The equipment is simple, and the amount of power
required is minimal.
And the result is something priceless.
Access to free, clean water.
The researchers say this could be a great solution
to the global water crisis,
by offsetting the need for about 70% of new
desalination plant installations in the next decade.
For example, a typical 600 megawatt power plant
could capture 150 million gallons of water a year,
representing a value of millions of dollars.
The researchers aim to test the system
at MIT's central utility plant in the fall.
The campus's power plant tests will not only
de-risk the technology, but will also help
the MIT campus improve its water footprint.
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Tackling the global water crisis

86 Folder Collection
jbsatvtac1 published on August 22, 2019
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