[HN Gopher] A new class of materials that can passively harvest ...
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A new class of materials that can passively harvest water from air
Author : Tycho
Score : 292 points
Date : 2025-05-26 13:14 UTC (9 hours ago)
(HTM) web link (blog.seas.upenn.edu)
(TXT) w3m dump (blog.seas.upenn.edu)
| DocTomoe wrote:
| Now make this a marketable power-less air dehumidifier. This is
| one of those 'changing whole industries' things.
| WalterGR wrote:
| Those exist in the form of dehumidifier bags, and they're
| inexpensive and easy to get. Does this material have benefits
| over what's currently in use?
| DocTomoe wrote:
| Dehumidifier bags are bulky. Surfaces, on the other side, can
| be folded into loops, which should increase the amount of
| humidity they can absorb.
| the__alchemist wrote:
| Surfaces as you describe go into the bags.
| fuzzfactor wrote:
| Never quit experimenting on _something_ worthwhile, for one thing
| so you 're always experimenting.
|
| The best things may come by accident, which is where it sometimes
| just starts to get good.
|
| But what are the difference in odds for someone who is constantly
| experimenting versus someone who experiments not at all?
|
| Regardless of what you really set out to accomplish to begin
| with.
|
| And which has the momentum to continue experimenting, even in the
| case of a major pivot?
|
| Looks like they really have hit the sweet spot and it's a bit
| like creating molecular sieves which are tuned to release the
| collected moisture without excess energy.
|
| Could also be harvesting a little ambient energy and working to
| "zone refine" the atmospheric fluid.
| gus_massa wrote:
| > _a new class of nanostructured materials that can pull water
| from the air, collect it in pores and release it onto surfaces
| without the need for any external energy_
|
| As a similar comment note, it's like a high tech Dehumidifier
| bag. https://www.amazon.com/Wisesorb-Moisture-Eliminator-
| Fragranc... The bags have Calcium Chloride and absorb water from
| unsaturated air and make small drops of water. It's obvious that
| they get depleted, and to use them again you must buy a new one
| or boil all the water to get the crystals again.
|
| In this new material, the droplets are attached to the material.
| To remove them you must use energy. They don't just drop to a
| bucket bellow the device magically. You can't use it to "harvest"
| water without energy. You can sweep the droplets with a paper
| towel, but now to remove the water from the paper towel you need
| energy.
|
| > _With a material that could potentially defy the laws of
| physics in their hands_
|
| This does not break the laws of physics. It would be nice that
| the PR department of the universities get a short course
| explaining that if they believe the laws of physics are broken,
| then they must double check with the authors and then triple
| check with another independent experts. Tech journalist should
| take the same course.
|
| Note that the bad sentence and the misleading title is from the
| university https://blog.seas.upenn.edu/penn-engineers-discover-a-
| new-cl...
| Evidlo wrote:
| When a publication I was involved in got a university PR piece,
| they were in direct communication with us
| Y_Y wrote:
| Amusingly, I have the same experience as you and GP. Thee
| university wants to hear what the researchers have to say,
| but subsequently they decide independently what they're
| writing, strict scientific honesty be damned.
| B1FF_PSUVM wrote:
| Honesty pays no bills for professional liars.
|
| Like diplomats, they're sent abroad to lie for their
| university, and the university president cries all the way
| to the bank for the sins of his hirelings.
| beloch wrote:
| University PR folk are sometimes quite scientifically
| illiterate. Their job is basically marketing. They need to
| turn an esoteric, jargon heavy, and heavily qualified paper
| into a hype piece that the money people can understand.
| _Everything_ must be a ground-breaking, world-shaking, all-
| time first. They sometimes make dubious claims no matter how
| many times you tell them not to. Ultimately, they report to
| the university 's money people and _not_ to researchers.
|
| If you want science, read journals. If you want to see who is
| likely to get more money, read university PR releases.
| wenc wrote:
| I've observed the same. University science PR pieces are
| usually unreliable -- they are optimized toward generating
| buzz than scientific accuracy. They usually link to the
| actual science papers, but the prose is usually a stretch.
|
| Even in this case -- "defying the laws of physics" is
| sensationalist narrative manufacturing.
|
| The real claim is actually more moderate, and the research is
| not really close to commercial yet.
| wenc wrote:
| It's research-in-progress, but I think the promise is slightly
| different from dehumidifier bags (also in other parts of the
| world, Thirsty Hippos [1]) which are single use.
|
| You're correct in that: (1) it doesn't break the law of
| physics; (2) to remove the droplets, you still need energy. But
| it sounds like if the droplets are moving to the surface, the
| energy needed to release the droplets could be far lower than
| most active dehumidification methods (e.g. Peltier junctions).
|
| [1] Thirsty Hippos -- which are very effective in small spaces.
|
| https://www.amazon.sg/Thirsty-Hippo-Dehumidifier-Moisture-Ab...
|
| Basically a supercharged silica gel.
| EA-3167 wrote:
| Those are usually just calcium chloride in a bag, it's very
| hygroscopic and fairly cheap... also makes a halfway decent
| de-icer. The issue I see with this thin-film method is that
| no mention is made of the rate of production at a given
| relative humidity for a given area of the film.
|
| It's interesting, but without the details (and with a lot of
| PR speak) I'm skeptical as hell about this in practice.
| the__alchemist wrote:
| Dehudifier bags (e.g. silica, CaCl) aren't single-use.
| Microwave, then reuse. Some even are color-changing so you
| know how much moisture they've absorbed.
| dotancohen wrote:
| Microwaving is adding energy, obviously. But the idea here
| is that the water is recoverable, not that the air is now
| drier.
| the__alchemist wrote:
| Concur; the idea behind this class of devices is to take
| advantage of a daily humidity cycle. Whether it's CaCl
| (absorption) or Silica (adsorption), or the latest lab-
| designed adsorption surface.
|
| This is a good time to note that I see one of these
| articles ~once every two years, for the past 10 years. I
| haven't observed one make it beyond the initial discovery
| phase.
| adnauseum wrote:
| This, and solutions for male pattern baldness.
| dotancohen wrote:
| By the 24th century, no one will care that you are bald.
| chiefgeek wrote:
| Unless you are Brian "Hairlacher" formerly of the Chicago
| Bears and shilling hair replacement on Chicago area
| billboards for years now.
| wizzwizz4 wrote:
| Male pattern baldness is a solved problem, if caught
| early enough; people just don't usually bother, because
| the cleanest solution (a 5a-RI) can interfere with sexual
| function, the "proper" fix for that (low-dose topical
| application) is time-consuming (so people normally just
| kludge it with Viagra), and the medicines involved can
| (indirectly) cause breast growth with prolonged use
| (unlikely to be a problem with low-dose topical
| application, and can also be mitigated, although
| overshooting that mitigation can cause osteoporosis) and
| are "don't even touch this if you're pregnant" class
| (they can interfere with foetal development).
| dotancohen wrote:
| If I have to relinquish my sexual function and grow
| breasts to reduce baldness, then baldness is not a solved
| problem.
| nagaiaida wrote:
| out of curiosity, what else would you expect the side
| effect profile of something mediating the effects of a
| potent androgen on the body to look like?
|
| it's not estrogen where you would _expect_ breast growth
| (and can 't count on any particular changes to sexual
| function anyway), it's inhibiting conversion of
| testosterone to dihydrotestosterone which _could_ have
| that effect, much like you could spontaneously develop
| gynecomastia without intentionally fiddling with your
| hormone balance. calling it unsolved sounds a lot like
| calling the very many conditions with medications that
| have more likely and worse side effects equally unsolved.
| wizzwizz4 wrote:
| > _it 's not estrogen where you would expect breast
| growth_
|
| Actually, it is. Reducing DHT levels causes the body to
| elevate both testosterone and oestrogen levels, via
| homeostasis. But yeah, it's not a _direct_ effect, and if
| it 's a problem you can twiddle further to make it go
| away. (You could even do that pre-emptively, though you
| normally get days and days of warning before breast
| development actually starts, so I'd advocate the "wait
| and see" approach.)
| wizzwizz4 wrote:
| Low-dose topical application doesn't have those problems.
| Heck, even "dose your entire body" doesn't always lead to
| sexual dysfunction. (And breast development is a rare
| side-effect that you'd notice before anything permanent
| happens, and is easily-addressed.) However, it _is_
| topical application of a medicine that can interfere with
| foetal development.
|
| Oh, almost forgot: any messing around with sex hormone
| levels puts you at risk of depression. That's big side
| effect #3 (though again, many people don't even notice
| it).
| throwanem wrote:
| Probably a small piezo junction could be used to provide a
| solid-state vibrator for releasing water from a
| proportionately considerably larger area of the material, or
| at larger scales perhaps a technique similar to the
| ultrasonic sensor cleaners built into interchangeable-lens
| cameras.
| dieselerator wrote:
| Do you mean like an ultrasonic humidifier[1]?
|
| [1] https://www.amazon.com/Ultrasonic-
| Humidifiers/s?k=Ultrasonic...
| throwanem wrote:
| Sure, why not?
| Aardwolf wrote:
| If something breaks the laws of physics it simply means the
| laws of physics were incomplete, so we update them and now it
| no longer breaks them
| therein wrote:
| It is really as simple as that and even applies to soon
| what will seem like free energy. It is not free energy, it
| is just energy from a field we were previously ignoring and
| previously fighting against.
| WalterBright wrote:
| Thanks for the explanation. My first thought reading the
| headlines was somebody thinks they discovered a perpetual
| motion machine.
| galangalalgol wrote:
| What is the theoretical limit on the energy cost to remove
| water from air? A dew years back 3m had some super
| inexpensive way that invovled a reusable water andorber that
| released its water under only slightly decreased pressure and
| slightly increased temperature. The incoming air and the
| waste heat from the downstream ac unit provided all the
| warming with the pressure change being all that was
| necessary. It had two banks so one could dump water while the
| other absorbed. It made the whole system rund double
| digiymore efficient than just the ac alone. And that was
| neglecting that the felt temperature would be lower with the
| dessicated air.
| chrisweekly wrote:
| > "remove water from air? A dew years back"
|
| "dew" was a funny typo there :)
| deadbabe wrote:
| Yes it is impossible to break the laws of physics. If they
| appear broken then it is only because our understanding was
| wrong. Similar, the laws cannot be "defied". You can only do
| what the universe allows, nothing more.
| mistrial9 wrote:
| this was certainly amazing to see (at least two years ago)
| vintermann wrote:
| Repost from four days ago:
| https://news.ycombinator.com/item?id=44060712
|
| Also, they do a really good job of making it sound like it
| violates thermodynamics. Since it doesn't, and dehumidifiers
| already do a good job of getting water out of air for the energy
| price you have to pay, there has to be some other selling point.
| Right? But I'm not sure I see it.
| bayindirh wrote:
| > there has to be some other selling point. Right? But I'm not
| sure I see it.
|
| Windtraps [0].
|
| [0]: https://dune.fandom.com/wiki/Windtrap
| detourdog wrote:
| or moisture vaporators
|
| https://starwars.fandom.com/wiki/Moisture_vaporator
| moffkalast wrote:
| But moisture farming? Really? A man of your talents?
| simiones wrote:
| Those exist, but, as the GP points out, they're called
| "dehumidifiers". Or sometimes clothes driers. The question
| was, what makes this new dehumidifier any better than
| existing dehumidifiers.
| bayindirh wrote:
| Windtraps are _passive_ , like this material. They work
| solely on temperature differential and wind.
|
| I'm not aware of any passive, solid state dehumidifiers
| which are not chemical, which condense water to a
| chemically loaded solution, which what a Windtrap is not.
| detourdog wrote:
| This would be passive and solid state.
| crazygringo wrote:
| > _dehumidifiers already do a good job of getting water out of
| air for the energy price you have to pay_
|
| They do a terrible job. Condensate dehumidifiers are as
| expensive to run as an AC, produce unwanted heat, and are
| noisy. Dessicant dehumidifiers are even less energy-efficient.
|
| If there's a way to extract moisture from the air with less
| energy and less noise, that would be huge.
| simiones wrote:
| So, is this new method less noisy and/or more energy
| efficient? The article doesn't really say.
| thfuran wrote:
| >without the need for any external energy.
|
| That sure seems to imply that there's no need for a noisy
| and power hungry compressor.
| vintermann wrote:
| It also seems to imply that it violates thermodynamics.
|
| It takes energy to condense water, so where does it get
| it? If it isn't external, it runs out.
| freeone3000 wrote:
| Condensation of water is exothermic. If you add a cold
| thing to the environment, ie, _remove_ heat from the
| water, the water will condense all on its own. This
| reaches steady-state when the cold thing is warm and the
| water is condensed. No thermodynamics issue!
|
| They're claiming they have a material that will do it at
| higher temperatures. Assuming such a material gets hotter
| as it works, there's no thermodynamics problem here.
| smus wrote:
| You are super confident a thing that exists can't exist
|
| https://en.wikipedia.org/wiki/Air_well_(condenser)
|
| Check out the passive section of the above
| kortilla wrote:
| Those depend on energy differentials so the sun is the
| external heat source.
| petesergeant wrote:
| Especially for somewhere like UAE that in summer has the
| upsetting combination of massive humidity, no rain, and huge
| water demand.
| ChrisMarshallNY wrote:
| Someone here once posted a link to a story[0] about the
| Persian Cooling Towers, that you see all over the ME.
|
| Thousands of years old, I think.
|
| [0] https://www.bbc.com/future/article/20210810-the-
| ancient-pers...
| JKCalhoun wrote:
| Perhaps OP was describing "swamp coolers" -- or evaporative
| cooling?
| thfuran wrote:
| That's the exact opposite of extracting moisture from the
| air.
| moffkalast wrote:
| Running a swamp cooler + dehumidifier that doesn't heat
| up would mean being able to do self contained cooling
| which would be a massive thing. Currently the only way to
| do that is with desiccant which needs recharging too
| often to be practical.
| relwin wrote:
| Tech Ingredients demonstrates how this works:
| "Revolutionary Air Conditioner!"
|
| https://youtu.be/R_g4nT4a28U?si=MoRSi1mOyHiVbZUr
| JKCalhoun wrote:
| You're right. I'll leave my original comment because I'm
| an idiot, ha ha.
| gus_massa wrote:
| > _If there 's a way to extract moisture from the air with
| less energy and less noise, that would be huge._
|
| _Less noise_ : I agree, but you still need some air flow so
| the corners of the room that are far away also get
| dehumidified. Perhaps a slow fan in enough, and when you run
| them slowly they are quieter.
|
| _Less energy_ : It's not clear that this uses less total
| energy. It's easier to imagine what is happening if you
| compare it to a high tech Dehumidifier Bag.
| https://www.amazon.com/Wisesorb-Moisture-Eliminator-
| Fragranc... But instead of sending the drops down, they get
| attached to the device. You can use it only once unplugged.
| Then you have to buy a new one or use energy to extract the
| water (like boiling the water of the dehumidifier bad until
| you get the crystals again). It's not clear if building a new
| copy of this is cheaper than building some new calcium
| chloride salts, and/or if regenerating the new device is
| cheaper than regenerating the calcium chloride salts (that is
| usually not done).
| lolinder wrote:
| Less energy would definitely be a huge plus but _unless_ this
| violates our understanding of thermodynamics there will still
| be unwanted heat put out into the air. The heat from a
| dehumidifier comes primarily from the latent heat in the
| water being released so that the water can become liquid.
| This heat _must_ be released somehow in this process unless
| they actually did find something that breaks our
| understanding of physics.
|
| Obligatory Technology Connections video on the topic:
| https://www.youtube.com/watch?v=j_QfX0SYCE8
| crazygringo wrote:
| That's true, but I was under the impression that most of
| the heat generated by current compressor dehumidifiers is
| just waste heat from the mechanical operation of the
| compressor itself. The phase change heat is there too, but
| it's significantly less. So there should still be a lot of
| room for improvement, theoretically.
| lolinder wrote:
| Yeah, there's certainly some of that, but going off of
| Alec's numbers and trial above you end up with a _larger_
| portion coming from the latent heat than from the
| mechanism, for the same reason that a heat pump is more
| efficient than an electric heater: it 's condensing more
| water than it is running mechanisms.
|
| That said, his demo is not under typical operating
| conditions in that a dehumidifier is normally expected to
| actually be able to catch up and reduce humidity in the
| room, while his demo ensures that the humidity levels
| stay high throughout the hour. So it's likely that under
| normal operating conditions the mechanism's proportion of
| the waste heat is higher than it is in his demo.
| cyberax wrote:
| > That's true, but I was under the impression that most
| of the heat generated by current compressor dehumidifiers
| is just waste heat from the mechanical operation of the
| compressor itself.
|
| Nope. It's almost all (>80%) latent heat. I believe, the
| theoretical limit is around 90% for typical room
| temperatures.
| leptons wrote:
| >The heat from a dehumidifier comes primarily from the
| latent heat in the water being released so that the water
| can become liquid.
|
| A dehumidifier movies heat from one side to another using
| electricity to do the work. One side gets cold so the water
| can condense on it, while the other side gets hot from
| extracting the heat from the cold side. Heat is still
| generated from this process even if there are 0 water
| molecules in the air and no water is collected. The water
| does not create the heat, the electricity does.
|
| I don't think there has to be any heat involved with
| collecting water molecules in the air into a larger volume
| of water, depending on the process used.
| NegativeLatency wrote:
| It's not just the electricity creating the perceived heat
| https://en.wikipedia.org/wiki/Enthalpy_of_vaporization
| lolinder wrote:
| Both processes create/release heat, and in Alec's tests
| in the linked video the bulk of the heat from the
| dehumidifier running in a humid space is coming from
| latent heat released from the water. That may not be true
| in regular operating conditions, but there will always be
| a substantial amount of heat released from the water when
| you trigger a phase shift.
|
| > I don't think there has to be any heat involved with
| collecting water molecules in the air into a larger
| volume of water, depending on the process used.
|
| The only other option is to increase the pressure in the
| room or in a space within the room, which this material
| pretty clearly isn't doing.
| nkrisc wrote:
| > I don't think there has to be any heat involved with
| collecting water molecules in the air into a larger
| volume of water, depending on the process used.
|
| For the water to condense, there must be heat given off,
| unless I'm fundamentally misremembering my high school
| physics class.
| tejtm wrote:
| state change takes 63 calories per cubic centimeter of
| H2O unless I am misremembering my high school science
| class.
|
| at least for water solid to liquid
| 90s_dev wrote:
| > If there's a way to extract moisture from the air with less
| energy and less noise, that would be huge.
|
| I vote we write to our legislators to update the laws of
| thermodynamics to enable this. Typically I would agree we
| should leave well enough alone, but in this case it seems
| like the benefits outweigh the costs.
| hackyhacky wrote:
| That's not how the laws of thermodynamics work.
|
| In reality, you would need to convene an international
| consortium to approve to the change, and the Chinese
| wouldn't sign on unless we agree to a temporary suspension
| of Newton's third law.
| 90s_dev wrote:
| We would only need a committee's approval if changing it
| would break things.
|
| I say we skip that process, test it in a lab somewhere in
| rural midwest where nobody lives, and see if gravity
| starts changing or whatever. As long as cows don't start
| to float in a 3 mile radius within 4-5 hours, that's
| probably good enough validation to move forward with
| changing thermodynamic legislation.
|
| [edit] we should also probably make sure the boiling
| point of water stays the same
| layer8 wrote:
| I'm not sure the constitution grants Congress that power.
| 90s_dev wrote:
| They already weighted in on the definition of p so why
| not?
|
| https://en.wikipedia.org/wiki/Indiana_pi_bill
| jcims wrote:
| It almost certainly doesn't violate our understanding of
| thermodynamics, but it's not clear that it would have to in
| order to condense ambient water vapor from the atmosphere.
|
| From the paper [1]:
|
| _Remarkably, when these amphiphilic nanoporous PINFs are
| exposed to high yet subsaturating conditions [i.e., relative
| humidity (RH) < 100%], macroscopic water droplets appear
| spontaneously on the film surfaces without the need for
| cooling, as illustrated in Fig. 1C and shown in Fig. 1D._
|
| 1 - https://www.science.org/doi/10.1126/sciadv.adu8349
| BenjiWiebe wrote:
| Well, when water changes from vapor to liquid, it releases
| heat. The heat has to go somewhere.
|
| Sorry, I don't know the correct physics lingo. Heat of
| enthalpy or formation or whatever.
| chasd00 wrote:
| Tangent but this may solve a mystery of mine. When I make
| scrambled eggs I add a little bit of water to make them
| fluffy. When I turn off the heat there's a puff of steam I
| can't explain. Since it seems to me more heat is needed to
| produce that extra puff of steam. However, maybe the fast
| condensing of the water vapor that happens when I turn off
| the stove produces a. I start of extra heat and therefore
| the steam?
| abracadaniel wrote:
| Maybe the drop in temp stops a Leidenfrost effect that
| was reducing the surface area of the food that was
| contacting the pan.
| jcims wrote:
| Is it gas stovetop?
|
| If so, it could be that the water vapor coming from the
| eggs no longer mixing with the hot gases coming from the
| flame around the pan, allowing it to drop below the dew
| temp (?) and allowing it to condense right above the pan.
| IOW the water vapor is always there, you just can't see
| it until it is able to condense in lower ambient temps.
| BenjiWiebe wrote:
| I don't think the fast condensing of steam would cause
| enough heat to cause more steam, though. Because the
| reason it condenses fast is because there's heat being
| removed from the system (cooling to the room, and no
| longer more heat getting added). So the heat is already
| "spoken for" - it's the reason that steam turned back
| into water.
|
| The other commenter that wonders if it's a gas stove
| might be onto something.
| jcims wrote:
| Sure, but it could get absorbed/radiated away in the base
| material.
| wrp wrote:
| If water vapor is condensing on the material, wouldn't there
| be a transfer of heat energy?
| pyinstallwoes wrote:
| Heat transfer is not transfer of heat energy
| scotty79 wrote:
| The idea here is that you don't need to cool down the air to
| get water.
|
| First you get water, and as a result material heats up a little
| bit, then it can cool down passively back to ambient.
| dang wrote:
| > Repost from four days ago
|
| Thanks! there were a few comments there and we'll merge them
| hither.
| PaulHoule wrote:
| See https://en.wikipedia.org/wiki/Air_well_(condenser) and
| https://en.wikipedia.org/wiki/Fog_collection and
| https://en.wikipedia.org/wiki/Atmospheric_water_generator
| Quarrel wrote:
| I'm so tempted to link this..
|
| Like, not even ironically.
|
| I know this isn't reddit and all, but, well..
|
| https://en.wikipedia.org/wiki/Dune_(novel)
| vasco wrote:
| Dew collectors are used in agriculture in deserts for real
| and I think in Dune too. Shaun Overton has a youtube channel
| where he's trying to revitalize a piece of desert and he has
| tried building some.
| downboots wrote:
| Not sure why it's downvoted. Fiction isn't as far from
| reality.
| kayodelycaon wrote:
| All of those rely on condensation, which is caused by
| temperature getting low enough the air can't hold water. The
| mechanism for the new material is completely different. It
| doesn't appear to require the air to be saturated.
|
| We already have substances that remove water from air. In those
| the water becomes absorbed. This seems to work on a similar
| principle. The real difference is the water doesn't stay
| absorbed.
| scotty79 wrote:
| This apparently can collect vapor (not fog) in ambient
| temperature, although the material heats up a little bit while
| absorbing water and needs to cool back down, which should be
| fine since when warm it's warmer than ambient air.
| salomon812 wrote:
| I wish they hadn't used "physics-defying" in their press release
| because I'm certain this is an important discovery for water
| condensers, but claiming it doesn't need an external energy
| source is massively negligent.
|
| I'm fairly certain they've created some form of a Brownian
| Ratchet: https://en.wikipedia.org/wiki/Brownian_ratchet
|
| People love to claim there's no external energy source, but then
| when you look closely, you'll find a hot-cold differential, and
| then you need external energy to maintain that differential. I'd
| put a large sum of money that either the material is colder than
| the ambient environment or the incoming moisture is warmer than
| the ambient environment. It might even be a differential within
| their material, and the lab lights are warming one side! There's
| a lot of passive devices that rely on the hot-cold cycle of day
| and night, that still counts as energy input from the sun.
|
| The article even mentions they tried to rule out a thermal
| gradient by increasing the thickness of the material, I'm not
| sure I understand why that would rule it out... the gradient
| would still exist.
|
| I hate this, because if they aren't intentionally supplying
| energy, it's probably really efficient (assuming they aren't
| taking samples out of the freezer or something) so it's still a
| big deal and important but apparently we have to claim something
| is a perpetual motion machine to get attention among the public.
| abracadaniel wrote:
| PET is a decent insulator, and they seem to be trying to ensure
| it wasn't the temperature difference causing condensation, but
| the nano structure itself. I'm assuming they were controlling
| temperature and humidity, so it would mean the material must
| get hotter, but that seems like it can also be passively solved
| with a radiator. What they are describing would be a pretty big
| deal and seems plausible.
| ajnin wrote:
| Yeah I understand the need for an university to make the news
| once in a while, and the fact that this made the front page
| here proves the effectiveness of the method, but the terms
| "Passively Harvest" and "Defies Physics" should be used very
| carefully in the context of a scientific publication, even
| though it's only a blog post so we don't expect peer-reviewed
| journal levels of rigor.
|
| I feel that it disserves science in the end, the belief that
| some magic material is going to break the second law of
| thermodynamics is closer to alchemy than chemistry.
| hollosi wrote:
| From the actual paper (
| https://www.science.org/doi/10.1126/sciadv.adu8349 ):
|
| "All measurements were performed at 20deg +- 0.2degC maintained
| by an air circulation system unless otherwise noted. The
| temperature of the films was controlled using a heating/cooling
| unit (THMS350V, Linkam Scientific Instruments, Salfords, UK) when
| necessary."
|
| So the latent heat is conducted away by the cooling apparatus,
| it's just not explicitly stated, to sound more sensational.
| cjbgkagh wrote:
| Ah that seems to explain it to me, if instead of presenting it
| as breaking some physics they should have said what actually
| makes it useful.
|
| My understanding of it now is that since it can work at a
| higher temperature in an environment where the ambient
| temperature is low enough the latent heat can be passively
| radiated away. Even if using an active heat pump the higher
| temperatures would allow for a more efficient process. A closed
| system would eventually reach an equilibrium but there is no
| need to maintain a closed system.
| Y_Y wrote:
| This point is essential though! As soon as I saw the headline I
| knew it couldn't be the full story (there's no free osmotic
| lunch).
|
| Is there a corollary to Betteridge's Law that says that popular
| science journalism will always overatate the result?
| gopalv wrote:
| > So the latent heat is conducted away by the cooling
| apparatus, it's just not explicitly stated, to sound more
| sensational.
|
| In theory, if that makes it hotter than ambient air in the
| process, that would be a good thing - usually we have to cool
| things down below ambient air to get moisture out.
|
| Not a good thing if you want to measure maximum moisture
| extraction, but cooling something to ambient temperatures is a
| much easier task.
| delusional wrote:
| Would this not invalidate the conclusions of the paper?
| considering they are not just claiming to form water droplets,
| but that they do so isothermally.
|
| It could still be a useful material, but the science would be
| bad.
| mppm wrote:
| Keeping the temperature constant with a thermostat is not an
| issue here. That would only explain things if the surface were
| kept cooler than the surrounding air (below the dew point), but
| from the description in the paper that does not seem to be the
| case. They basically claim that macroscopic droplets form
| spontaneously from an unsaturated vapor. And no, this is not
| something permitted by the second law of thermodynamics.
| dotancohen wrote:
| > And no, this is not something permitted by the second law
| of thermodynamics.
|
| If someone points out to you that your pet theory of the
| universe is in disagreement with Maxwell's equations--then so
| much the worse for Maxwell's equations. If it is found to be
| contradicted by observation--well these experimentalists do
| bungle things sometimes. But if your theory is found to be
| against the second law of thermodynamics I can give you no
| hope; there is nothing for it but to collapse in deepest
| humiliation.
| lolinder wrote:
| -- Sir Arthur Stanley Eddington, The Nature of the Physical
| World (1927)
| robertclaus wrote:
| While I generally agree that it sounds dubious, this argument
| depends on whether the entropy of the liquid in the pore is
| lower than the entropy of the vapor in the air in the pore. I
| could see a highly hydrophilic capillary restricting a vapor
| enough to where it has better entropy in a liquid state.
|
| If that's true we just need to balance energy, which the
| cooler does.
| mppm wrote:
| > I could see a highly hydrophilic capillary restricting a
| vapor enough to where it has better entropy in a liquid
| state.
|
| My other comment here (and and a reply to a similar
| question) has more detail [1], but in short: this is true
| for capillaries and pores, it is _not_ true for
| "collectable" droplets on a flat surface.
|
| 1. https://news.ycombinator.com/item?id=44099078
| ChuckMcM wrote:
| I think the work stands out anyway. Unlike adsorption
| techniques there is zero change to the mechanism which just
| keeps pulling water from the air. Presumably, they will put a
| layer of this material on aluminum to conduct the latent heat
| and have something that just produces water full time, without
| additional energy input. consider a 'cube' of fins of this
| stuff sitting in shade with a collection bucket underneath it.
| It will be interesting when they build something like that how
| many liters/day it can extract from ambient air and under what
| conditions.
|
| Devices like that would be essential during 'wet bulb' days
| where the temperature and water content of the air created
| dangerous conditions for people. A passive device that takes no
| energy and just sucks water out of the air? Could be a
| lifesaver.
| cyberax wrote:
| To conduct the latent heat away, the aluminum sheet needs to
| be below the ambient temperature of the condenser plate.
| ChuckMcM wrote:
| You didn't read the paper did you :-). First, it isn't a
| "condenser" (which is kind of the cool science here) it is
| more of a molecular sieve that exploits two materials (one
| that repels, and one that attracts) the molecule in
| question (water). The water vapor is "forced[1]" together
| by the nano-structure, which result in a phase change
| (vapor to water) and that phase change releases heat into
| the nano-structure (and pushes the liquid water out to the
| surface) which makes the nano-structure warmer than the
| ambient temperature. The aluminum conducts that heat and is
| convectively radiating it into air on surfaces not covered
| with the nano-structure.
|
| The researchers also noted that the water that was
| expressed to the surface of the material did _not_
| evaporate (as one would expect). There some interesting
| speculation as to why that is. It wasn 't clear whether or
| not the water would move across the nano-structure if it
| was affected by gravity (aka dripping) but I can imagine
| several ways to transport it off the surface so I'm sure
| the researchers can too.
|
| [1] The description in the paper is that capillary action
| forces the vapor into the interior of the structure where
| it collapses into liquid.
| cyberax wrote:
| I read it. It sounds like nonsense.
|
| This is basic thermodynamics, you can do however much
| hydrophobic/hydrophilic nanomaterials, but you won't get
| condensation unless you somehow conduct away the latent
| heat. This can be done by storing energy in the material
| itself (that's how desiccants work), or by providing a
| temperature gradient (a cooler).
| ChuckMcM wrote:
| Okay I think we're saying the same thing, but let me
| check that..
|
| > This can be done by storing energy in the material
| itself (that's how desiccants work)
|
| This is exactly where the energy goes. From the paper (in
| it's Materials and Methods section) -- _All measurements
| were performed at 20deg +- 0.2degC maintained by an air
| circulation system unless otherwise noted. The
| temperature of the films was controlled using a heating
| /cooling unit (THMS350V, Linkam Scientific Instruments,
| Salfords, UK) when necessary._
|
| So the hypothesis is that the heat in the water vapor
| goes into the nano-pore material, which in their
| experiment they were _actively_ maintaining at 20 degrees
| C. So yes, they are actively removing the heat created by
| the phase change.
|
| One difference with desiccants is that once they are
| saturated you have to restore them through heating them
| up, but this stuff doesn't have that property. And while
| it may sound like nonsense it was reproduced in another
| lab[1].
|
| Apparently capillary condensation is a thing, its the
| popping out of the liquid water that was unexpected.
|
| [1] _With a material that could potentially defy the laws
| of physics on their hands, Lee and Patel sent their
| design off to a collaborator to see if their results were
| replicable._
| nullc wrote:
| You could coat them with an ultraemissive material and
| point them at the sky, if its not cloudy it will get
| significantly below the ambient air temp.
|
| But the paper suggest that it will condense at ambient
| anyways, because it gets warmer so radiation to ambient is
| enough for it to work.
| TJSomething wrote:
| Another part from the paper that a lot of people here seem to
| be ignoring: "Specifically, macroscopic water droplets
| isothermally form when the NP size is <=22 nm, RH is >~90%, and
| phPE ranges from 0.05 to 0.35." and "Initial water droplets
| that are observable under optical microscopy (~1 mm in size)
| appear within a few seconds after being exposed to 97% RH."
|
| This is really moist air that's only barely short of forming
| dew. A lot of people are focusing on sensational "violation of
| physics", when it's an incremental improvement on process that
| happens naturally.
| ChiMan wrote:
| Uses in AC and clothing seem like obvious use cases.
| andrewrn wrote:
| This is pretty cool! Basically changes the thermodynamic delta
| required for a condensation-evaporation cycle from climatic
| mediation to material mediation.
|
| What if you could eventually program the pore size? This would
| mean you could change the inflow/outflow balance of the
| reservoirs on-demand. Imagine smart clothing. Hot out -> increase
| pore size so the material dumps water, cold out -> pore size
| shrinks so the water is less likely to evaporate.
|
| I am peeved by the "violates physics" verbiage in the article
| though.
| wheelerwj wrote:
| Is it just me or does extracting moisture from the air seem like
| a really bad idea?
| B1FF_PSUVM wrote:
| I take it you do not live on the south or east coast of a
| northern hemisphere continent?
|
| People there usually have a surplus of moisture in the air most
| of the time.
| circles_for-day wrote:
| This seems like it could be improved with ai-assisted molecular
| dynamics that have been in the news for drug discovery and
| protein folding.
| lightedman wrote:
| We did something similar to this in the middle of the Mojave with
| carbonate rock, charcoal, and a big corrugated metal tube.
|
| It produces about 3 gallons of water a night.
|
| 34.997387, -116.380048
|
| See the big tube sticking up? There's a miner's hotel built
| there.
| fblp wrote:
| Got a link to how this was made?
| lightedman wrote:
| I do not, I'm sorry. Basically the bottom is charcoal for a
| filter, the top is porous carbonate rock to catch moisture
| from the air, and the large metal tube serves as a way to
| heat things up and then at night chill down below ambient a
| bit faster so that water condenses out of the rock and drips
| through the charcoal and through piping to a water collection
| system.
| davedigerati wrote:
| With respect to energy balance comments and comparing this to
| other technologies: both processes of absorption and condensation
| are happening within the same material passively, meaning you do
| not need to put energy into it. The heat gained from absorption
| is lost in the next step of condensation. The impact of this
| discovery, therefore, is that you don't need the power of your AC
| or your dehumidifier or your moisture vaporator on the south
| ridge.
|
| Always testing the AI's I thought this might be a fun one to
| watch how they think through it since it is about technology that
| they would not have been trained on. Grok thought through the
| process more thoroughly than I (B.S.ChemE) would've .
|
| https://grok.com/share/bGVnYWN5_e80e8100-3682-4157-879e-c5ca...
| gus_massa wrote:
| Grok is wrong. The description violates the second law of
| thermodynamics. But I don't blame Grok, the PR is very
| misleading.
| mppm wrote:
| Unless they have buried some really important caveat somewhere in
| the paper [1], it really looks like they are making claims that
| are incompatible with the second law of thermodynamics. They
| claim that water droplets are condensing on their nanomaterial
| _at constant temperature_ and _less than 100% relative humidity_.
| This is absolutely forbidden by thermodynamics as we understand
| it. Under these conditions droplets can condense _within_ pores
| (forming a concave surface), but they can never form a convex
| droplet on a _flat_ surface.
|
| Their mumbo-jumbo about water being "squeezed out" onto the
| surface by the hydrophobic component is totally bogus as well.
| The condensation will just stop earlier, without overflowing.
| Water condensing in concave pores and being squeezed into convex
| droplets requires hydrostatic pressure to be positive and
| negative at the same time.
|
| The possibilities I see are: 1) contaminated surfaces 2)
| miscalibrated relative humidity or 3) they've neglected to
| mention a cooling plate that keeps the material below ambient.
|
| 1. https://www.science.org/doi/10.1126/sciadv.adu8349
| a1371 wrote:
| I'm not sure what's forbidden here. You don't need 100%
| relative humidity to grab water from the air in fact in any
| wood has a moisture content that in equilibrium is in relation
| to the air moisture content. The moisture diffuses into every
| material and evaporates based on where it finds less vapor
| pressure. That's why you may have dry lips at 40% RH versus
| moisturized lips at 70% RH.
|
| What you're referring to is condensation and is caused by air
| oversaturation due to a temperature drop which doesn't seem to
| be the case here.
|
| Theoretically speaking, you can have a material that somehow
| absorbs high moisture from the air but has microscale
| properties that promote creation of droplets then somehow these
| droplets are separated from the rest of the air (with something
| like a smart vapor retarder, a passive material) and the water
| gets harvested.
| mppm wrote:
| What you are referring to is called capillary condensation
| [1]. When you have a hydrophilic surface with thin
| capillaries or small pores, they can pull water from the air
| below 100% RH. However, this process requires an enclosed
| space with a very small radius and the air-water interface is
| _always_ concave in this case (it 's just how capillary
| forces work).
|
| Forming a convex surface, on the other hand, requires an at
| least slightly hydrophobic material and produces a positive
| internal pressure. This is a key difference, because
| condensation into a hydrophilic pore is favorable in terms of
| free energy, while condensing onto a hydrophobic surface is
| unfavorable (unless you have a supersaturated vapor).
|
| > Theoretically speaking, you can have a material that
| somehow absorbs high moisture from the air but has microscale
| properties that promote creation of droplets then somehow
| these droplets are separated from the rest of the air
|
| That "somehow" is what makes the paper's claims impossible.
| The water condenses spontaneously into the pore because it
| thereby _lowers_ its free energy. Extruding it onto the
| surface is then even more unfavorable than direct
| condensation. Unfortunately, no passive system can achieve
| this feat, no matter how cleverly nanostructured, as it would
| go against the arrow of increasing entropy. You need an
| external energy source to drive that process.
|
| 1. https://en.wikipedia.org/wiki/Capillary_condensation
| fuddy wrote:
| I think people are being too critical in the comments.. I see
| nothing requiring free energy or physics defying in an ideal
| condensation material. This process is going on all the time in
| less optimized materials and we usually are not happy about it.
| (There's also a very interesting logical argument that we only
| exist because the water molecule has such unusual properties
| compared to its environment.)
| elil17 wrote:
| People need to understand that the minimum energy required to
| separate water from air is much higher than the minimum energy
| required to separate water from salt. This fact of physics means
| desalination will always be more efficient than water harvesting.
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