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Light can make water evaporate without heat

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Re: Light can make water evaporate without heat

#121

Post by cyanydeez »

elil17 wrote: post #118
farhanhubble wrote: post #116

Earlier quoted context omitted.

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?

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.

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

Re: Light can make water evaporate without heat

#123

Post by bdd8f1df777b »

malfist wrote: post #95
montjoy wrote: post #71

> The researchers found that the effect varied with color and peaked at a particular wavelength of green light. I wonder if this affects photosynthesis in any way? IIRC plants are green because chlorophyll does not absorb that color. Maybe that’s partially because green light induces too much evaporation?

Maybe, but evaporation is critical for plants. They don't have a heart to pump blood and supply nutrients, they have to rely on evaporation to move nutrients from the roots up

Well, the chloroplast was evolved when all life forms were submerged in the sea

Re: Light can make water evaporate without heat

#124

Post by JohnFen »

elil17 wrote: post #87
JohnFen wrote: post #75

Earlier quoted context omitted.

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 thos…

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.

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?

Re: Light can make water evaporate without heat

#125

Post by jagged-chisel »

waldothedog wrote: post #120

Any one else familiar with “solar vapor drive” in the building science community (vapor being driven into buildings from the outside simply due to solar exposure)? My understanding is that it is expected even in the absence of warmth. Is this the same effect?

> … even in the absence of warmth.

Tangent (adjacent?): my ice “cubes” evaporate. (They’re hollow cylinders) If I put into my freezer more ice than I can use in a week, about half of the top layer of blocks has lost quite a bit of their substance.

Re: Light can make water evaporate without heat

#126

Post by jacquesm »

bdd8f1df777b wrote: post #123
malfist wrote: post #95

Earlier quoted context omitted.

Maybe, but evaporation is critical for plants. They don't have a heart to pump blood and supply nutrients, they have to rely on evaporation to move nutrients from the roots up

Well, the chloroplast was evolved when all life forms were submerged in the sea

The sea is on the other side of a very carefully policed barrier.

Re: Light can make water evaporate without heat

#128

Post by grishka »

m463 wrote: post #80
elil17 wrote: post #44

Earlier quoted context omitted.

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 intermolecula…

> 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)

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.

Re: Light can make water evaporate without heat

#129

Post by jordan_curve »

grishka wrote: post #128
m463 wrote: post #80

Earlier quoted context omitted.

> 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)

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.

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

Re: Light can make water evaporate without heat

#130

Post by tjmc »

grishka wrote: post #128
m463 wrote: post #80

Earlier quoted context omitted.

> 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)

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.

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