> Sorenson notes there is more than three quadrillion gallons of water in the air, which is essentially a massive untapped resource.
For what it's worth, air with low humidity can be pretty damaging. Lots of materials would become excessively brittle at very low humidities, causing them to break easily. This interesting white paper [1] suggests that, for most materials, the optimal humidity is between 40-60%.
The device in India shown there produces 15 liters of water per square meter per year. The surface area of a bottle is, say, 500 square cm, or 1/20 of a square meter. That would produce about a liter in a year.
Clearly, some efficiency gains are needed w.r.t. those designs to effectively make the claim "water bottle tha fills itself". Whether that is possible, I don't know.
It may be, yes, but Wikipedia isn't convinced. Even further down, it states:
"Zibold's condenser had apparently performed reasonably well, but in fact his exact results are not at all clear, and it is possible that the collector was intercepting fog, which added significantly to the yield.[10] If Zibold's condenser worked at all, this was probably due to fact that a few stones near the surface of the mound were able to lose heat at night while being thermally isolated from the ground; however, it could never have produced the yield that Zibold envisaged"
That made me look for more recent data. That PDF from 2005 was the best I could find.
Hmm air can carry a few grams of water per kG of air [1] and 1kG of water is one liter, so if you can pull 1g of water out of each kG of air you need 1,000 kG of air. Stole this from wikianswers: "Each mole has a volume of 22.4 liters and a mass of 28.97g/mol at STP, therefore a cubic meter of air is 1.293 kg at 0o Celsius on the coast. An average mass of 1.2kg per m3 at room temperature and standard pressure is often used as a rule of thumb." so that would suggest about a thousand cubic meters of air flowing past this bottle's extractor area to get one liter of water out of the air.
Good work. I imagine 1g/1m^3 is roughly what you'd expect - especially in a desert.
If the extractor area is the size of the bottle's cap (2cm x 2cm = 4e-4m^2) then to get a litre of water (1e3 m^3 air) requires 2.5e6m of air to flow past it - If you want it full in a day that's 30m/s... hmmm... doesn't seem likely.
However if the size of the extractor area is as large as the bottle (say 10cm x 10cm = 1e-2m^2) then a 1 m/s wind may do it.
Based on this I'm not confident in the "marathon runner" claim, but I'm sure techniques for extracting water from wind have been used before, but improvements could be made.
i think you're confusing collecting area with airflow cross-section. they're completely different things, unless somehow the air is blowing through the side of the (solid) bottle.
Not really. This volume of air has to make contact with the bottle, whatever the collecting area's shape. Imagine loosely fitting a tube around the neck of the collecting area. All the air has to pass through that tube.
no, i'm saying that only a small fraction of the incident air will touch the surface. most will flow around - probably laminar flow containing a stagnant area of higher pressure directly in front of the obstacle.
you are calculating the swept volume. but only a small fraction of the swept volume "makes contact" (ie is roughly within the mean free path of a water molecule) with the collecting surface (which appears to be necessary here for water to be extracted).
with netting your argument is closer to being correct. but this is an impervious bottle, not a net.
if you implemented the tube you suggest (and i understand that was simply an illustration to explain swept volume) then pressure would increase in the tube slowing flow and/or flow would be predominantly around the edges, with, again, a stagnant higher pressure region in the centre.
Well, think of the most efficient collector of water (and sunshine) you can. Water bottles have to look like that, or at least .. have a spigot you can attach a bottle to ..
My question is what kind of contaminants (or none!) this process picks up - If you're getting your water from a polluted atmosphere (say, LA), what kind of pollutants end up in your water? Or does it produce "ultra-pure" water, leading to weird health risks like hyponatremia?
You won't get hyponatremia from overly "pure" or distilled water. The amount is water is utterly dwarfed by the amount in food.
If there are pollutants in air they will be in the water, but it's not a actually a problem because, although they might be bad to breath, most air pollutants are harmless when eaten.
Carbon (soot), Ozone, NOs, sulfur dioxide (smog), etc are harmless to eat.
But if there were it would be something that requires acid or digestion to "activate". Or perhaps something that can't be absorbed without something the only exists in the gut.
Bacteria actually could do that. Inhaled they would rapidly die, but in the gut they could live (more food for them) and cause illness.
Also, the gut will absorb things faster than the lungs. So I could easily imagine a toxin that has little effect when inhaled (since it's absorbed too slow to cause damage) but causes trouble when eaten (everything is absorbed at once).
This may be a stupid question, but if the device requires power in order to move air over the water-collecting surface, would it work without power if it were outside in a breeze? Or is there something about the air flow in terms of its characteristics or location in/on the device that requires a manufactured flow?
I guess the airflow is to make it more efficient. In high humidities, you can easily collect 1 liter potable water with a 3m2 plastic sheet, a clean recipient, a hole in the ground and some sunlight, or just hot weather. It's an old survival trick. His apparatus is a kind of upgrade.
The plastic sheet process is different from the one in the article. In the case of the plastic sheet, you are baking the water out of the ground, not extracting it from ambient air. It seldom works well in practice, because you get a little condensation under the sheet, but it's not enough to run in rivulets into the jar, and when you DO get a few drops in the jar, the same process that is baking the water out of the dirt evaporates it from the jar. You end up shaking the plastic, lifting it up and licking it.... Works better in theory than in practice.
But imagine that, instead of a special water bottle, you have a poncho-sized sheet of coated plastic in the shape of a windsock with a coiled wire ring at the opening and a pouch at the end. If this could work like the beetle's wings and take water out of the ambient air, that would be interesting.
I spent some time learning from a respected survival expert who claimed the 'solar still' was not an efficient use of one's energy. I tried it out a couple of times anyway and proved to myself that he was right.
What did work fairly well was a transpiration bag [1]. It took a few bags to get a meaningful supply of water and one needs to be careful about the foliage used.
To get water out of the air, it has to be condensed into liquid. Condensation requires a significant temperature difference, and the best way to get that is refrigerant. I'm surprised that he was able to do this using only a solar powered fan.
You could create condensation with only a light breeze, but it probably wouldn't yield a significant amount of water. I think the best case for these would be to attach them to balloons and put them high into the atmosphere (where it's much colder), so that they could produce even more water with the same amount of energy.
My read is that the coating doesn't need a manufactured flow (after all, the beetle that inspired it doesn't) put it's very possible they'll make a bottle with a surface that requires it, say, a conch shell.
(MIT, 2011) "In some field tests, fog harvesters have captured one liter of water (roughly a quart) per one square meter of mesh, per day. Chhatre and his colleagues are conducting laboratory tests to improve the water collection ability of existing meshes."
If I might channel my inner grumpy-old-man for a moment:
I find it curious that people who design nifty new devices are regularly referred to as "scientists". This is not science; it is engineering. Why not call it that?
Because the guys in this story are actually scientists, doing the discovery and research, as well as engineers .. and it is 'implied' that scientists can do engineering also, so I guess its Venn diagram time .. ?
I like what Cliff Stoll had to say about this... "The first time you do something it’s science. The second time it’s engineering. A third time it’s just being a technician" -- Ted Talks, 18 minutes with an agile mind.
Well, if we assume that any source of alcohol could be counted as beer, this device could be constructed by combining the water generator with a colony of modified algae (or an ecosystem of carb leaking algae and yeast) combined with some sort of membrane that allows alcohol through but not water. (Or a Brownian motion powered still).
That sounds pretty hard, but it would be a safe bet to say you could buy one within fifty years. Maybe longer if you want something nicer than pure ethanol.
This might be the first case of biomimicry on the front page :). This was one of the entries in our 2011 Biomimicry Student Design Challenge [1]. It's pretty exciting to see how far they've taken it from concept to funding [2] in a short amount of time.
This sounds nifty, but what I'd love to know is, what's the rate of filling, for an apparatus that's small enough to be roughly bottle-sized? Obviously many of the technical details (battery size, etc) are still being worked out, but I'm betting that rate of condensation is already known---and it's an important constraint.
Yeah, they talk about using it for runners but how quickly does it fill? Would it require a full marathon length to fill a single water bottle? It may still be practical even if that's the case. I'd like to know more.
My first thought was it would be fantastic for backpacking (in high humidity) if the fill rate is high enough and if it didn't need batteries or heavy solar panels or anything. Water adds a lot of weight when you have to carry it. If I could just sip an ounce at a time and not ever have to carry it on my back, I'd literally be a happy camper.
This is one of those "didn't see it coming" technologies that really has the potential to change things. Could this disrupt the bottled water industry? Make it so that water pipes are a thing of the past ("wireless" for water)?
I realize that extraction rates are probably slow right now, but imagine this technology n years from now.
It would be neat to see this used with homes and businesses. Combine with a cistern for catching rainwater, and use for (at least) the non-potable uses (laundry, lawn, toilets) and you could significantly reduce the water burden on reservoirs and aqueducts.
You can see more about collecting water out of the air at http://blogs.ei.columbia.edu/2011/03/07/the-fog-collectors-h... . Having lived in the Atacama desert I know there are already ways to do it and am very curious about the efficiency of this new system. In coastal northern Chile conditions are about as perfect as possible but it is still a slow process.
This could be good news for farmers who could perhaps create a closed loop within greenhouses to draw water from the air that the plants originally exhaled.
Most dehumidifiers are basically an air conditioner. They cool down a coil and draw air over it to cause the water to condense out.
This sounds like some sort of nanotech approach that causes the water to condense without needing a temperature change. It may not even require any power, if you can accept a slow rate of water collection.
This is a fabulous technology, but we shouldn't get carried away. Firstly, this is another disruption of the world's water cycle, which we have already managed to a considerable degree, and if we manage atmospheric water extraction on a massive scale, we will wreak havoc with the climate (again).
And even if you do it on a massive scale nothing at all will happen.
We have these enormous oceans on earth, and if the air gets dry more water will simply evaporate from the ocean. It takes about a month for air to completely circle the globe - and a whole lot less than that for air from any particular place on earth to reach the ocean.
So even if you completely dry out air in one spot it'll be replenished within a day or two at most. Meaning that overall you never will actually dry out the air.
And remember that on a global basis water is more or less never created or destroyed. So any water you capture from the air, will just end up right back in the air.
You water a plant and it converts the water to hydrocarbons, those hydrocarbons are then eaten, and are "burned" and are converted right back into water.
Same for the water you drink - it's only in your system temporarily, it will end up in the environment again later.
For what it's worth, air with low humidity can be pretty damaging. Lots of materials would become excessively brittle at very low humidities, causing them to break easily. This interesting white paper [1] suggests that, for most materials, the optimal humidity is between 40-60%.
Still, this is a very cool concept.
[1] http://www.descoenergy.com/pdf/Humidity%20How%20it%20affects...