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...
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.
It's interesting, but without the details (and with a lot of PR speak) I'm skeptical as hell about this in practice.
From figure 4 (& backed up by simulation fig 3E) it looks like stuff begins to happen only at 97% relative humidity & after a few minutes (at micrometer scale)
https://www.science.org/doi/10.1126/sciadv.adu8349
Granted, it's almost easy enough to try at home: melt some poly gloves into "freeze dried" silica powder
I'd assume if the amount of energy required to collect the water is low then we're looking at something interesting.
For context, that amount of heat is five times the amount needed to heat 1kg of liquid water from 0° to 100°C (without thawing or boiling it). So it's not in any way a trivial amount.
If you want science, read journals. If you want to see who is likely to get more money, read university PR releases.
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.
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.
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.
Obligatory Technology Connections video on the topic: https://www.youtube.com/watch?v=j_QfX0SYCE8
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).
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.
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.
Sorry, I don't know the correct physics lingo. Heat of enthalpy or formation or whatever.
First you get water, and as a result material heats up a little bit, then it can cool down passively back to ambient.
Windtraps [0].
Thanks! there were a few comments there and we'll merge them hither.
"All measurements were performed at 20° ± 0.2°C 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.
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.
> And no, this is not something permitted by the second law of thermodynamics.
If that's true we just need to balance energy, which the cooler does.
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.
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.
Their experiments suggest that tiny water droplets appear inside the material at 70% RH (relative humidity). If this is true, then I expect there is a way to extract the droplets using very little energy. Ideas:
- make open collection points on the film
- use ultrasound to bounce the droplets around and consolidate them
- make the film on a material that can be saturated with water so the new droplets can easily join the flow
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.
Is there a corollary to Betteridge's Law that says that popular science journalism will always overatate the result?
It could still be a useful material, but the science would be bad.
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.
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.
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.
Water harvesting in pristine lab conditions may break down rapidly in realistic scenarios. Something that’s wet attracts dust and microbes. Dust plus water means more microbes. You’ll have lichen growing on this stuff in no time.
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.
Like, not even ironically.
I know this isn't reddit and all, but, well..
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.
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.
Seems to me that if you have a device that requires no extra material consumable input that's pretty interesting? Plenty of places with access to electricity that could benefit from the lack of other material input in theory.
If you have power, you can harvest water from the air wherever you are. Desalination generally requires trucking the water from the ocean to you.
I don't have the slightest idea whether transportation costs can ever be large enough to make water harvesting more efficient?
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.
People there usually have a surplus of moisture in the air most of the time.
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...
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.
There's no free lunch, but removing water from a fabric matrix is a well understood process. Thats what washerwomen have done for millenia.
Put one of these next to every tree. Or lines of them along rows of crops.
Run one in homes to make your ac more efficient and manage humidity.
Collect water on mountains or tall buildings and make hydro power?
Keep your pool topped off.
Basically Let salt water saturate the air in a closed system and use these to collect the water.
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.