Tuesday, August 4, 2009

Wringing Water out of Desert Air

The desert, by definition, has little no moisture. You would expect desert air to be as dry as... well, desert air. Why bother trying to squeeze water from it?

Turns out, desert air isn't that arid after all. Israel's Negev desert, for example, is humid enough to hold 11.5 milliliters (ml) of water in every cubic meter of air. Granted, 11.5 ml is a little more than 2 teaspoons, and 2 teaspoons of water don't go far toward slaking a thirst or boiling an egg.

But think of all the cubic meters of air piled above the 17.4 billion-square-meter (6,700 square miles) area of the Negev. The amount of water trapped in the air within 1 meter of the ground alone shoots to 17.4 billion times 11.5 ml, or 200 million liters, or about 53 million gallons.

Got your attention, did I?

Now, the point: Two German organizations have found a way to extract the moisture from desert air and convert it to potable water using only renewable energy.

Scientists at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart and at Logos Innovationen developed the process.

In their method, hygroscopic brine runs down a tower-shaped unit, where it absorbs moisture from the surroundings. This diluted brine is then sucked into a tank by a vacuuming process. Solar collectors heat the tank.

Because the brine is in a vacuum, it boils at a temperature considerably lower than 100 degrees C. Thus the solar collector doesn't need to work as hard as it would have under normal atmospheric pressure.

The heat from the solar collector boils the water. The evaporated water -- minus the brine -- is condensed and poured down a tube, ready for human use. The weight of the water column helps create the vacuum in the tank, negating the need for a powered vacuum pump.

The leftover brine, freed of the atmospheric water it had absorbed, runs down the tower again, gathering more moisture from the air.

Any electrical power needed by the system is supplied by photovoltaic cells. Which, like the solar collectors, get their power from sunlight.

Which, by definition, is something else the desert has an abundance of.

The scientists have tested prototypes of this system in the lab. Next step: a live demonstration.

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