Drinking water from air humidity
June 5, 2009
Plants producing large quantities of drinking water from moisture in the air could look like this. Credit: Logos Innovationen
Cracks permeate the dried-out desert ground, the landscape bears testimony to the lack of water. But even here, where there are no lakes, rivers or groundwater, considerable quantities of water are stored in the air. In the Negev desert in Israel, for example, annual average relative air humidity is 64 percent - in every cubic meter of air there are 11.5 milliliters of water.
Research scientists at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB in Stuttgart working in conjunction with their colleagues from the company Logos Innovationen have found a way of converting this air humidity autonomously and decentrally into drinkable water.
"The process we have developed is based exclusively on renewable energy sources such as thermal solar collectors and photovoltaic cells, which makes this method completely energy-autonomous. It will therefore function in regions where there is no electrical infrastructure," says Siegfried Egner, head of department at the IGB. The principle of the process is as follows: hygroscopic brine - saline solution which absorbs moisture - runs down a tower-shaped unit and absorbs water from the air. It is then sucked into a tank a few meters off the ground in which a vacuum prevails. Energy from solar collectors heats up the brine, which is diluted by the water it has absorbed.
Because of the vacuum, the boiling point of the liquid is lower than it would be under normal atmospheric pressure. This effect is known from the mountains: as the atmospheric pressure there is lower than in the valley, water boils at temperatures distinctly below 100 degrees Celsius.
The evaporated, non-saline water is condensed and runs down through a completely filled tube in a controlled manner. The gravity of this water column continuously produces the vacuum and so a vacuum pump is not needed. The reconcentrated brine runs down the tower surface again to absorb moisture from the air.
"The concept is suitable for various sizes of installation. Single-person units and plants supplying water to entire hotels are conceivable," says Egner. Prototypes have been built for both system components - air moisture absorption and vacuum evaporation - and the research scientists have already tested their interplay on a laboratory scale. In a further step the researchers intend to develop a demonstration facility.
Feb 08, 2010
However, it is not clear how the deliquescent brine will be cooled so that it's vapor pressure is less than the partial pressure of the atmospheric moisture during the scrubbing phase. I doubt the vacuum evaporative cooling will be sufficient in such a hot climate. Same cooling issues may exist for the distilled water condensed in the barometric leg.
An air conditioned lab is one thing, but what happens in the desert?
any comments
LOL, moisture farmers?
But how much water can one of those thing produce?
Because that "single person units and plants" doesnt like like they'll be little.
i can definitely see where hes going with this...
if an area over a land mass averages say 1" of rain per year..if you then suck the additional moisture from the air in that locale, thereby decreasing the rate of evaporation of water into the clouds, you should logically lower the rainfall even further, and the amount of decrease being directly proportional to the amount of water taken from the air in that area.
i will say, the thing here not being taken into consideration is the fact that clouds circulate/move at different rates...therein it may not effect just the areas to the east of the air dryed locations :)
Assume initial air conditions 30 degC, 20% RH. Each 100 cu m of air will contain 3 x .2 = 0.6 kg water. The total water content of the 5 cu km of air is 5x10^6 x 0.6 = 3x10^6 kg. The unit will extract 1 x 10^3 kg, or 1/3,000th of the air's water content. 0.03%
The total water content of the 5 cu km of air is 5x10^6 x 0.6 / 100 = 3x10^4 kg. The unit will extract 1 x 10^3 kg, or 1/30th of the air's water content. 3%