Water out of desert air

[KNSSoftware]

Uh oh, can you smell, what I can smell...  Eau de BS, Dave style

http://www.sciencemag.org/news/2017/04/new-solar-powered-device-can-pull-water-straight-desert-air

[mtdoc]

That is a summary of a legitimate scientific research article published in Science - one of the 2 most prestigious scientific journals in the world (the other one being Nature).

It's about as far from BS as it gets.

I agree with Wilfred - the "debunking" meme is way past it's prime. It may work well as click-bait, but an unfortunate side effect is it leaves many unable to distinguish between real science/engineering and solar-roadways type BS. 

[Hensingler]

It's about as far from BS as it gets.

Looks like BS to me or at least abysmal reporting. Titled "This new solar-powered device can pull water straight from the desert air" they show a drawing of what looks like a cube shaped box with this MOF material on the roof and very specifically state

The setup works so well that it pulls 2.8 liters of water out of the air per day for every kilogram of MOF it contained

Maybe someone can check my figures but cool desert air at 10% RH weighs about 1.25kg/m^3 and contains 0.1% water by weight. To extract 2.8l of water they need to pass 2250 m^3 of air across their MOF material and extract 100% of the water content. What size box does it need to get good 'contact' between 2250m^3 of air and its 'roof' during a night and why would the air want to flow through the box anyway? Are they going to have solar cells and batteries and fans?

Then there is the problem with reversing the process where in a hot sunny desert you have to get rid of substantial amounts of heat to keep the bottom of the box cool enough to condense.

[mtdoc]

The quality of reporting is a judgement call and in any case is not really relevant to the veracity of the findings in the source journal article.

I'd suggest you read the original source article in Science.  Then, if you feel you're qualified to question Kim et al.'s methods or dispute their data I'd love to hear why and so would  the editors  of Science as well as the peer reviewers of the journal article.

If you have a valid criticism of their methods or data, you could write a letter to the editor of Science and it will be published.  In doing so you would instantly achieve some notoriety in the scientific community.

If that sounds sarcastic - it really is not meant to be.  Findings published in Science are widely read in the scientific community and hold great weight. Careers are literally made by having a research article published in this journal. If there is a fundamental flaw in the methods or data of an article published there, then publishing that could in itself could make a career 

[Karel]

Nothing new:

http://edition.cnn.com/2014/04/24/tech/innovation/machine-makes-drinking-water-from-air/

http://water-gen.com/

[mtdoc]

Nothing new:

 

[Akra]

In contrast to the waterseer this concept actually works!

After reading the article the only big criticism I see is that the 3l of water per kilogram MOF seems a bit high,
the test results I saw in real world testing were always clearly under 1l per kg.
But it wasn't exactly the same device, it was much simpler as it was only a proof of concept.

Short explanation of the science behind it:

The MOF is like a sponge on a molecular scale and has the ability to absorb water, like e.g. silica gel does (the little drying packs shipped with most electronics for this reason)
and therefore the dew point is higher for this material.
But it doesn't hold the water as good as for example the silica gel does, especially when you rise the temperature the water can easily be removed again.
Therefore rising the temperature of the water-saturated MOF creates a high humidity atmosphere in the box,
rising the dew point to the level that the water can condense at the head sink at the bottom.
After condensing the water you need to let the MOF cool to ambient temperature and simply repeat the cycle over and over again...

[Kleinstein]

The concept with the water absorber is different from just pure cooling. This way it also does one more step: depending on the selectivity of the absorber it can also provide purification - this simple cooling method is more like producing water with quite some dust inside. So it still needs purification.

However this system will not work in all areas. There are deserts with a soil that has water adsorbing properties too - this causes a surprisingly low humidity at night too, because the soil also cools and essentially work the same as the MOF. This can be so bad as having less than 5% RH even at night. At this level very little, if at all humidity can be caught. However there are also deserts where chances are really good.

The 3 L number, like the number from the other cooler type systems seem to be valid for best conditions - so maybe in a coastal region or rain forest, where humidity at night is near 100%.

[Hensingler]

And the same story badly reported here
http://news.berkeley.edu/2017/04/13/device-pulls-water-from-dry-air-powered-only-by-the-sun/

Dry air does not contain any water for starters.

Again they claim 2.8l in 12 hours from 1kg of MOF material and say there is room for improvement because the current MOF can only absorb 20% of its weight in water. How is that supposed to add up? The reporting of this story has Batteriser levels of BS.

edit: I hadn't noticed the above story includes a video which clearly shows a large peltier module on top of the relatively huge heatpipe CPU cooler used as a condenser. They seem to have glossed over that and the large solar panel that would be required to power it from the sun.

[Kleinstein]

One could operate the cooling/ absorbing and heating/de-sorbing cycle several times a day. However 14 cycles with full absorption sounds like a lot. So it should at least not that it might be 2.8 L in 12 hours with sun and 0 L for the next 12 hours in the dark. So more like 2.8 L in 24 hours.

From the pictures the prototype looks like very much smaller - so 1 kg of absorber might actually be quite a big unit. Without a fan (and supporting PV) the system would also need some wind.

At least the required level of 20-30 % RH sounds like reasonable. In a real desert this might mean it will not work every day, or only parts of the day and of cause only when the sun shines. At least 20-30% RH should be easy to obtain if sea water is available; one might even provide some additional cooling this way.

[josecamoessilva]

Maybe I should take this as read, since we're on an engineering forum but:

Device used for an experiment =/= proof of concept =/= prototype =/= final deployable product.

What's shown on the videos and photos is not a prototype; in some it's the experimental rig they used to measure the properties of 1.8 g of MOF, in some others it's a proof-of-concept device with 1.3 g (that's grams, not kg) of MOF, with a lot of additional instrumentation attached.





Because they wanted to test different temperatures in the experiment, they attached a Peltier effect cooler to the system, just like a plane model inside a wind tunnel has a mount that can change the model's angle of attack and that doesn't mean that real planes need mounts. Given that it shows in some photos, some might assume that Peltier cooling is part of the device (it's not, the paper is very clear on that; the solar energy is used for heating the MOF and releasing the moisture).

Must agree with others who think "debunking" has jumped the shark. This being a Science paper and all, a real debunking is a rejoinder sent to the journal for peer review and publication; at least if the debunker is, say, a professional chemist who makes YouTube videos for extra cash.

Must applaud Dave's answer in another thread,

I have zero knowledge in this area.

If this post reads a bit testy, that's the result of me having to defend IHTFP & Berks U.

(The images above are screencaps from the Science paper. Sorry about the size, no idea why they came out so big.)

[Hensingler]

Peltier cooling is part of the device (it's not, the paper is very clear on that; the solar energy is used for heating the MOF and releasing the moisture).

So what in the proof of concept rooftop experiment kept the condenser at a stable and substantially below ambient temperature if it wasn't the 'not part of the device' peltier?

[mtdoc]

I'll reserve the right to object to the deliberate omission of the latent heat of vaporization from the energy balance of a device designed to condense water vapor, thank you very much.  That makes me an engineer, not a philistine. 

Huh? Can you explain how that is relevant? In any case, water's latent heat of vaporization is known (as is its heat of condensation which might be more relevant here) and it's a given that anyone with a serious interest in their research already knows this.   Temperatures are documented in the paper.  Have you read it? 

  Factual and science-based debunking of pseudoscience, when done well, is not passé. 

I agree. The problem arises when those who are doing the debunking (or proposing it be done) are unable to distinguish between genuine science and pseudoscience.

The other problem is when those with technical expertise in one field assume they have sufficient expertise to adequately evaluate something in any technical field.

It's one thing to do a "busted" type youtube debunking video on some crowdfunded type marketing scheme but quite another to do one on a peer-reviewed research article or even a privately funded research or engineering project being developed by reputable scientists or engineers.  Sure, if one has real background and expertise in that area - then a serious, data-driven critque is fair game - but I've seen none of that here or in some recent youtube videos.

The big concern I have is that contrary to the goal of debunking pseudoscience, this trend seems to be encouraging those without any expertise in a particular field to feel qualified to say "BS" to real science or engineering - just because it seems unlikely to them or it doesn't "smell right" ,etc. - or because their favorite youtube video blogger does a debunking video on it.

IMHO that is no better than the type of science denying that the anti-evolution, anti-vaccine or AGW doubters flourish in.  Seeing even hints of that kind of thinking here on this forum just depresses me.

[donotdespisethesnake]

An idea for a product floated in a blue sky scientific paper may be as completely impractical as a bogus crowd-funded project, but one should not equate both as being bad science. Typically, stuff in science papers:
- the science is sound - ie. works in the lab (probably, subject to peer review etc)
- may not work as well in the field
- the engineering may need a LOT of work
- the economics may not be there at all

In particular, the paper notes that Zirconium at $150/kg would not make it practical, and a cheaper material would be needed. A lot of puffery around science papers is created by the PR dept and then the popular press.

[Codebird]

I think much of the dismissal here is due to the field being plagued with scams (Waterseer? Self-filling bottle? That stupid metal leaf thing?). Once people have seen a series of devices claim to make bulk water from desert air, all of which were conclusively dismissed as unworkable, of course they will assume the same is probably true of anyone else who makes the same claim.

I don't know if this can work or not. The materials science is beyond me. As best I can tell, it's using a novel water-absorbing material to concentrate the very low humidity in the air, a process powered by day/night temperature difference - one thing that a desert usually has plenty of. Even if it can in principle though, the engineering issues are going to take years to solve, so it might just be a case of the PR department taking the actual research and running with it.

[ConKbot]

It's about as far from BS as it gets.

Looks like BS to me or at least abysmal reporting. Titled "This new solar-powered device can pull water straight from the desert air" they show a drawing of what looks like a cube shaped box with this MOF material on the roof and very specifically state

The setup works so well that it pulls 2.8 liters of water out of the air per day for every kilogram of MOF it contained

Maybe someone can check my figures but cool desert air at 10% RH weighs about 1.25kg/m^3 and contains 0.1% water by weight. To extract 2.8l of water they need to pass 2250 m^3 of air across their MOF material and extract 100% of the water content. What size box does it need to get good 'contact' between 2250m^3 of air and its 'roof' during a night and why would the air want to flow through the box anyway? Are they going to have solar cells and batteries and fans?

Then there is the problem with reversing the process where in a hot sunny desert you have to get rid of substantial amounts of heat to keep the bottom of the box cool enough to condense.

2250m3, over 8 hous of night time, or 4.6m3/min. Easily achievable with a 40 watt fan (looking at one on digikey right now)  Who says this has to be a completely passive thing? Cover a roof with a box with the adsorber on the top of the inside, solar panels on the outside, with good contact between them and the box. Solar panels get hot, driving off moisture from the adsorber, and generate electricity to run a small refrigeration compressor that condenses the water (way more efficient than peltiers used in a test rig)  and charges the batteries to run fans overnight.

It's just a demonstration of the new material and a demonstration of a potential application with a lab setup that isn't a 100% fleshed out ready to produce design.  Save the fits of rage for shitty authors who write articles saying how it's going to change everything, rather than a lab demo of new materials tech. I.E. "NEW BATTERY UNLOCKS CHARGING PHONES IN 5 SECONDS" headline after a university assembles  nanolithium battery with atomic microscope, can charge in 5 seconds, but is in no way shape and form mass manufacturable yet.

[Kleinstein]

The system does not need a temperature below ambient - though a low temperature can help a little.

Judging from the size of the proof of concept with a little less than 2 g of MOF and maybe 1/100 of a m² in size. A 1 kg unit would be around 5 m².  2.8 L/ day / kg of MOF sounds a lot more attractive than maybe 1 L / m² / day. Of cause the demo unit is not build to be effective with the solar heat.

From the science side, the interesting part would be whether the MOF is actually better than more conventional absorbing materials like zeolites.

[LabSpokane]

I'll reserve the right to object to the deliberate omission of the latent heat of vaporization from the energy balance of a device designed to condense water vapor, thank you very much.  That makes me an engineer, not a philistine. 

Huh? Can you explain how that is relevant? In any case, water's latent heat of vaporization is known (as is its heat of condensation which might be more relevant here) and it's a given that anyone with a serious interest in their research already knows this.   Temperatures are documented in the paper.  Have you read it? 

(I deleted my original post 5 mins after writing it because I realized I don't even want to debate this stuff anymore, but here I go anyway.)

I haven't gotten past the paywall yet, but what I'm referring to was the media summary of the scientist's research which claimed the basis for a liquid water production device - which is a far cry from what the scientists only wish to discuss: "it absorbs lots of water vapor."  Also, the article in question was substantially amended to make the claims far less spectacular than in its original publication. 

Once the claim was made that this invention was for the creation of liquid water, I don't recognize one's right to eliminate what we all learned in Physics 101 - the latent heat of vaporization plus the efficiency of the condenser - which has a massive impact on the practicality of an energy claim.  If one doubts this, I would like to direct said one to a nearby thermal power plant to witness the size of the condenser. 

All that needs to be done is to keep the claims within the system boundaries.  That's really not a lot to ask of a professional scientist, is it?

[josecamoessilva]

In particular, the paper notes that Zirconium at $150/kg would not make it practical, and a cheaper material would be needed. A lot of puffery around science papers is created by the PR dept and then the popular press.

This was the problem with cadmium-telluride solar cells a while ago. Great performance in the lab, until someone noticed that tellurium is as rare as platinum (on Earth, that is; apparently not so in the asteroid belt), so no way to produce them at scale.

As Don Sadoway said about grid-level storage batteries, if you want them dirt-cheap, you have to make them out of dirt (i.e. abundant elements).

[mtdoc]

Once the claim was made that this invention was for the creation of liquid water, I don't recognize one's right to eliminate what we all learned in Physics 101

Original research journal articles do not review basic principles for good reason.  As for media reports meant for mass consumption - well that's another issue. But it is probably not easy to strike the right balance between informing the general public of a new finding and educating them on underlying scientific principles at the same time (which would surely drive away many readers)

All that needs to be done is to keep the claims within the system boundaries. 

This is a good illustration why critiquing a media report on a scientific finding is not the same as critiquing the research or journal publication itself.  We all know how good the media is at getting technical reporting right..

As far as I can tell based on my admittedly non-expert reading of the journal article, there are no such unreasonable claims made.  But far more important than my opinion is the opinion of the peer reviewers who are experts in the field (and likely rivals of the PIs) and the opinion of the editor of Science. These people do this for a living and have reputations at stake.

[LabSpokane]

Once the claim was made that this invention was for the creation of liquid water, I don't recognize one's right to eliminate what we all learned in Physics 101

Original research journal articles do not review basic principles for good reason.  As for media reports meant for mass consumption - well that's another issue. But it is probably not easy to strike the right balance between informing the general public of a new finding and educating them on underlying scientific principles at the same time (which would surely drive away many readers)

All that needs to be done is to keep the claims within the system boundaries. 

This is a good illustration why critiquing a media report on a scientific finding is not the same as critiquing the research or journal publication itself.  We all know how good the media is at getting technical reporting right..

As far as I can tell based on my admittedly non-expert reading of the journal article, there are no such unreasonable claims made.  But far more important than my opinion is the opinion of the peer reviewers who are experts in the field (and likely rivals of the PIs) and the opinion of the editor of Science. These people do this for a living and have reputations at stake.

Once again, I have to point out that the article was EDITED, so what you're reading now is a toned down version of the original, which claimed that 3.5L of water could be obtained from a few grams of material. 

Critique of these mass media science articles does matter to a certain extent.  They are usually the basis for a seemingly infinite number investment schemes into technological applications for this research.  Think what you will, but there is an enormous amount of society's capital being wasted on schemes founded on these claims.  The original article had more than a faint aroma of this.  That was the basis of my comment.  I have little doubt about this new material being capable of absorbing the amount of water vapor that is claimed.  That is not my point. 

[josecamoessilva]

Don't abracadabra with technical words, please.

This isn't specifically directed at any of the comments above, but it pains me to see engineers use words as if they were incantations rather than technical concepts that have precise meanings.

To wit: talking about "thermodynamics" or "enthalpy of evaporation" without taking a minute to do some calculations. And no, you don't need to read the Science paper or solve the heat equation to avoid wrong statements.

The point of contention is the 3 liters of water per kg of MOF per day. So, how much energy are we talking about and how big a surface to dissipate it?

The enthalpy of evaporation for water is 2.3 MJ/l and because it's so high you can pretty much ignore the energy of temperature change within the gas or liquid phases; only the phase change matters to a first approximation.

3 liters times 2.3 MJ/l = 6.9 MJ - per day, therefore (divide by 24*3600) 80 W of power.

(At this point most engineers should realize that there's no problem; 80 W from a metal surface in open air will almost surely be peanuts. A human being radiates about 100-200 W depending on the level of activity, or at least that's the number used for HVAC dimensioning when I was in college, back in the Pliocene.)

How big an area are we talking about? Again, even without reading the paper we can do some basic calculations, assuming planar geometry for the MOF deposition.

If the MOF were as dense as lead, 11.34 kg/l, a thin(ish)-film deposition over the base material, say 1/25 mm, would lead to 2.2 m^2 of area, or a square about 1.5 m on the side. To dissipate 80 W. Piece of cake.

But since the MOF is much less dense than lead and is deposited to maximize porosity (that's how the MOF works, it's all physics, no chemistry), it's more like styrofoam, and the area would be around 24 m^2, which makes the "enthalpy of evaporation problem" a non-starter. (It was already a non-starter with 80 W in 2.2 m^2, but the 24 m^2 is closer to reality.)

(The actual geometry of the deposition is more complex, highly non-planar, making use of a copper foam that is infused with the MOF powder, all on a copper substrate, but to know that you'd need the actual paper.)

We are engineers; let's not act like muggles and resort to lobbing words around as if technical terms were incantations. If it's an engineering word, there are probably numbers hiding behind it somewhere. Get those numbers.

You shall know the numbers, and the numbers shall set you free.

[mtdoc]

Once again, I have to point out that the article was EDITED

Well I guess that's part of the confusion here. I really have not read the media reports closely -I assumed they're inaccurate (nothing new there).  I've been talking about the actual journal article which documents the science as the authors meant. That has not been edited since publication. I have paid little attention the the media reports or the Science News article which it appears you're focused on.

As far are the Science News article. Looking at it shows it was edited on March 14th at 12:28pm (likely EST)- before all but maybe the first 2 posts in this thread. If they corrected an error then good on them -that may be relevant to a discussion of news reporting but it's not relevant to the science under discussion here.

Honestly, I'd be shocked if there were no errors in the media reporting - but that's not the science.

Which gets back to my original concern - people seem to be mixing the 2 up and in some cases (I'm not pointing at anyone here) unable to distinguish real science from media reporting or worse from pseudoscience. That's scary IMO.

[Hensingler]

(At this point most engineers should realize that there's no problem; 80 W from a metal surface in open air will almost surely be peanuts.

How can you write drivel like that with even mentioning temperature? You can dissipate 80W from something the size of a pin, but, water does not condense on incandescent tungsten.

It is more like 160W anyway because at a guess it spends half the day absorbing water.

The question is can you practically dissipate 160W from a condenser maintaining a temperature differential between it and the solar heated MOF that allows extraction of all the water in the MOF. If you can why didn't their proof of concept roof top experiment try to prove that instead of using a peltier device to hold the condenser at a substantially below ambient 24C?

[LabSpokane]

(At this point most engineers should realize that there's no problem; 80 W from a metal surface in open air will almost surely be peanuts.

How can you write drivel like that with even mentioning temperature? You can dissipate 80W from something the size of a pin, but, water does not condense on incandescent tungsten.

It is more like 160W anyway because at a guess it spends half the day absorbing water.

The question is can you practically dissipate 160W from a condenser maintaining a temperature differential between it and the solar heated MOF that allows extraction of all the water in the MOF. If you can why didn't their proof of concept roof top experiment try to prove that instead of using a peltier device to hold the condenser at a substantially below ambient 24C?

Yup.  Right here.