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A simple device that can capture its own weight in water from fresh air and then release that water when warmed by sunlight could provide a secure new source of drinking water in remote arid regions, new research from KAUST (King Abdullah University of Science & Technology) suggests.
At the heart of the device is the cheap, stable, nontoxic salt, calcium chloride. This deliquescent salt has such a high affinity for water that it will absorb so much vapor from the surrounding air that eventually a pool of liquid forms.
The full research paper is available on-line.
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(Score: 1, Interesting) by Anonymous Coward on Monday December 10 2018, @09:57PM
This yet-another-free-water-from-air-machine is also a glorified dehumidifier. However instead of a heat pump style dehumidifier, this is a dessicant dehumidifier. Such systems certainly work, you can buy them on Amazon.
On Earth the dry air will still have water vapour so it's "merely" a matter of scale, you must process correspondingly more air to get the similar amounts of water out, which in practice probably means a larger facility. That's a problem in its own right but it's probably not an insurmountable problem with the concept. Nevertheless, there are major problems with the concept of using dessicant dehumdifiers as a drinking water source.
Most obviously, dessicants normally are extremely toxic—I doubt this one is any exception—which is why when you find things like silica gel in product packaging it has a big warning on it saying "DO NOT EAT, THROW AWAY". Yeah, just what you want mixed in your drinking water supply. So you will need to treat the output of the process anyway, and then one quickly realizes that access to liquid water in the world is not really a problem humanity needs to solve; access to safe water is.
The more serious problem is that dessicant dehumidifiers don't do anything to avoid the thermodynamic implications of condensing water. There is no way around it: turning liquid water into water vapour involves putting a very large amount of thermal energy into that water (about 2.2MJ/kg), and the reverse is exactly the opposite: you must take all that energy back out (i.e., about 2.2MJ/kg must be removed from the water vapour). In the case of a dessicant this involves some sort of chemical interactions so it's maybe not as simple to think about as a heat pump, but essentially all the energy input to actually make this work happen will be in the processing of the reagents.
As usual, it will be substantially cheaper and easier to load up a fleet of 50 tonne tanker trucks with potable water sourced from a lake halfway around the world and drive it wherever you need the water than it will be to use "free" water from air machines for drinking. That's why these systems are invariably stupid: it is just too energy intensive (-> expensive!) to condense water for the purpose of drinking it.