[elil17]

Thermodynamics and evaporation are my day job and I think most other explanations here are missing the point. Evaporation normally occurs when individual water molecules have enough thermal energy to break their intermolecular bonds, leaving the bulk liquid and entering the air.

In this case, they found strong evidence that water molecules were being removed in groups of several water molecules. Because intermolecular bonds aren't being broken in these groups, the amount of thermal energy needed to cause them to enter the air is less than if they had evaporated as individual molecules. These groups later break apart in the air, absorbing thermal energy from the air and leading the air temperature to decrease slightly a few millimeters away from the sample surface.

Evaporation happening as clusters of molecules is weird - it's very different from how evaporation usually works. I'm not really sure whether to even call it evaporation since I don't think the clusters would fully qualify as vapor until they are broken apart into individual molecules.

[m463]

> I'm not really sure whether to even call it evaporation

I can't help but think of ultrasonic humidifiers/misters, which use vibration to do evaporation-adjacent kinds of things.

I also wonder if specific wavelengths of light are involved (sort of how 2.4ghz microwaves work on water)

[grishka]

Water particles produced by an ultrasonic humidifier are larger than those of real steam. I know it because I have one and if I run it for long enough, everything gets covered in a nasty white residue, probably salts from the water. Real evaporation doesn't do that.

[ponyboy123]

I think the difference is that evaporation creates water vapor, whereas an ultrasonic dehumidifier is creating water droplets, some of which are very small, but are still droplets that can carry minerals from the water

[tjmc]

Most datacentres ban the use of ultrasonic humidifiers for exactly this reason.

[jordan_curve]

isn't it generally recommended to use distilled water in these humidifiers for exactly this reason?

[Modified3019]

Yep, both the minerals, and the microorganisms breeding in the water get thrown into the air.

For constant use, I personally recommend "evaporation humidifiers" that use a wick and fan to induce evaporation. The wick will need to be replaced every several weeks.

[dr_dshiv]

Cue “burning” salt water video: https://youtu.be/e8utkoK2DhA?si=t2cvuu4V-hFKFjM8

I’m still blown away that radio frequencies can dissociate hydrogen without an electrode. I haven’t read a good explanation of the phenomenon.

[sheepscreek]

Ever heard of a Plasma gun? Or pressurized water cutting? Heck Lasers do the same thing.

In every case, it’s really a collision between different particles at various energy levels, leading to different results.

Take an extremely fast neutron and collide it with an atom, and you could alter the chemical composition of the atom/end up with a different element (basic principle of breeder reactors). Fascinating stuff.

[_nalply]

I wonder how strong the radiation was. If strong enough it dissociates and then by burning it gives back the energy... Looks like a fake perpetuum mobile...

[dr_dshiv]

Yeah, obviously strong enough to make the energy balance. But still awesome.

[_nalply]

Yes it's awesomeness reminds me of the Tcherenkoff light I once saw with my own eyes. It was a deep pool of a test reactor and I even asked the guide if I am allowed to put my index finger into the water. It was warm. I looked long and deep at the fascinating white-blue light in the water.

It is so awesome that no public relations work is needed. The thing speaks for itself and is so convincing.

[araes]

I suspect you're correct, at least partially.

My personal suspicion is that the light waves are hitting the extremely diffuse binder material and then ejecting the water light a billiard ball or a solar sail effect. It may have a resonance (vibration) with the binder structure. See below image for example of binder material.

https://upload.wikimedia.org/wikipedia/commons/d/d3/Short-pe...

[sheepscreek]

This was also my first thought! And they seem to cool the air nearby. The above explanation makes sense (where bonds are broken in the air).

[hawk_]

So a watched kettle might boil faster?

[tzot]

Did you get a green light to make that joke here?

[dfex]

well played

[aatd86]

You emmit green light from your eyes?

[LoganDark]

If you have green eyes, yes.

[layer8]

Being green in the face should be sufficient.

[elil17]

One more thought for how to explain this, for those who don't want to worry about intermolecular bonds and what energy goes where:

Essentially they found that light makes a "splash" when it hits water (at least in certain circumstances).

[elil17]

Worth noting that I’m going off the preprint since I don’t have PNAS access.

https://arxiv.org/pdf/2201.10385.pdf

[syntaxing]

But in a closed system, the energy to boil or evaporate the same amount of water is the same right? As in, you still have to pay the energy price but evaporating all the water is probably easier engineering wise?

[elil17]

Yes, that’s exactly right! Although I would caveat that and say that we don’t know whether it is actually useful engineering-wise.

[depereo]

'clumped vapor' might be way more effective for cloudseeding

[elil17]

Yes, although the molecule clusters evaporate rapidly after they leave the surface

[gpm]

Even if they're in a high humidity environment where you could plausibly seed a cloud in the first place?

[elil17]

Thinking about this again, and I'm not sure. On one hand, yes, you could theoretically see a situation where the clusters want to grow because there are so many water molecules around them. But normally we seed clouds with much, much larger aerosols. Larger diameter = different (more favorable, I believe) surface energy.

[JohnFen]

Speaking as an person ignorant of this entire field, it seems to me that if it's the case that groups of molecules are breaking off rather than individual ones, the total energy required would be less.

But it's comparing apples to oranges, because the "end product" is different. In one, you have a cloud of individual molecules. In the other, you have a cloud of molecule "clumps". If you take it further and break those clumps down to individual molecules as well, I expect the total energy input would match that of evaporating water in the normal way.

To the experts reading this, am I close?

[elil17]

You’re thinking about it right if you’re zoomed into the surface of the water plus a few millimeters above it. But the molecule clusters themselves evaporate after that, which pulls heat from the air.

[JohnFen]

Gotcha. That heat from the air is also energy input that has to be counted, so it still would equal out in the end, right?

[elil17]

Exactly

[JohnFen]

So a good analogy might be that it's like a tiny version of what happens in an atomizer. It takes more energy to evaporate water than to turn the same amount of water into a very fine mist. The droplets will then evaporate on their own, using an amount of energy equal to the difference between evaporation and misting.

Thank you, I've got a little clearer view of my world.

[itishappy]

Sounds good to me. Energy is a function of state, so if you start and end with the same state, it'll require the same amount of energy. If it takes less light to knock loose bigger clumps, it'll take additional energy from somewhere else to break them up. The remainder will probably come from thermal energy from the air and water, but you could also use something like a laser or chemical reaction.

[klysm]

(armchair science) it seems like if a bigger bunch breaks off, you get better heat transfer from the increased surface area and it would evaporate much faster. Probably the same energy price but much more rapidly applied

[bloopernova]

Do photons hitting the surface of water transfer any kinetic energy?

Does the evaporation occur as soon as the light is switched on, or does it take a while to get started?

[frud]

Thank you. This is the first thing I've read about this story that is at all coherent.

[foota]

What happens if the air is saturated? Does the molecule clump just settle back down where it came from, or would it stay suspended somehow in the air (mist?)?

Alternatively, I wonder if this could be used as a super swamp cooler, I'm picture water dripping or flowing from a tube, a laser causing it to "burst apart", and then the droplets formed rapidly cooling the surroundings due to their surface area.

[smolder]

It seems possible we could improve swamp cooling with this, as with desalination, though in general you want to avoid putting energy into the system, I think. Powering a laser might overcome the benefits... unless you shot lasers in from outside? Even so, it might be best to use [filtered?] natural light for such a system.

[thsksbd]

Once airborne, the little droplet would be below the critical radius of water and have to absorb heat from air and fully evaporate.

[Modified3019]

>I'm not really sure whether to even call it evaporation since I don't think the clusters would fully qualify as vapor until they are broken apart into individual molecules.

Sounds like a chance to coin a suitably obtuse and prim science name, like Prosocial Evaporation, as opposed to Solitary Evaporation.

Gregarious and perhaps Convivial Evaporation are also good candidates.

[farhanhubble]

I had this understanding too from university physics but now that I think about it why do we assume each molecule has to break away independently. Why can't lumps of molecules break away as long as the group has enough energy to sever bonds with the rest of the bulk?

[elil17]

Well it’s not that it never happens, it’s just that it’s not particularly likely. Heat is disordered kinetic energy, so most often molecules won’t be traveling in the same direction.

[cyanydeez]

from my understanding, water is typically colloidal, so it would make sense that there's no symmetrical bonding to adjacent molecules and that could easily lead to groups being evaporated.

in many cases, layman's science is oversimplified for the benefit of college science. this might be the case

[thaumasiotes]

> I'm not really sure whether to even call it evaporation since I don't think the clusters would fully qualify as vapor until they are broken apart into individual molecules.

It's simple. You have a small puddle of water on the ground that slowly rains up into the air. ;D

[galangalalgol]

Light Induced Nano Aerosolization

Everything needs an acronym.

[godshatter]

ENAA

[geoffcampbell64]

Is there anyway in which this effect could be used to create a new type of heat pump?

[pomtato]

Interesting, reminds me of Microwave Emitter from Batman :D