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Light can make water evaporate without heat

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Re: Light can make water evaporate without heat

#61

Post by klysm »

syntaxing wrote: post #60
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…

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?

(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

Re: Light can make water evaporate without heat

#63

Post by galangalalgol »

elil17 wrote: post #44
frud wrote: post #17

I can't wrap my head around this story. What does it mean in thermodynamic terms? Isn't there a fixed amount of energy per mass that it takes to convert liquid water into vapor? Why does it matter that the energy comes from light?

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…

Light Induced Nano Aerosolization

Everything needs an acronym.

Re: Light can make water evaporate without heat

#64

Post by elil17 »

syntaxing wrote: post #60
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…

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?

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

Re: Light can make water evaporate without heat

#65

Post by hawk_ »

elil17 wrote: post #44
frud wrote: post #17

I can't wrap my head around this story. What does it mean in thermodynamic terms? Isn't there a fixed amount of energy per mass that it takes to convert liquid water into vapor? Why does it matter that the energy comes from light?

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…

So a watched kettle might boil faster?

Re: Light can make water evaporate without heat

#66

Post by 101011 »

klysm wrote: post #62

This is really cool, but I'm confused how we haven't stumbled into this before? Wouldn't this be quite obvious under some napkin math or does it have more to do with the specific hydrogels they were using?

This makes me think about a story that Richard Feynman told about experiments and how often people miss the most important part about cargo cult science. Here was him talking about how we got better and better resolution around the charge of an electron:

> Why didn’t they discover that the new number was higher right away? It’s a thing that scientists are ashamed of—this history—because it’s apparent that people did things like this: When they got a number that was too high above Millikan’s, they thought something must be wrong—and they would look for and find a reason why something might be wrong. When they got a number closer to Millikan’s value they didn’t look so hard. And so they eliminated the numbers that were too far off, and did other things like that. We’ve learned those tricks nowadays, and now we don’t have that kind of a disease.

https://calteches.library.caltech.edu/51/2/CargoCult.htm

Re: Light can make water evaporate without heat

#67

Post by tzot »

hawk_ wrote: post #65
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…

So a watched kettle might boil faster?

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

Re: Light can make water evaporate without heat

#68

Post by dheera »

pard68 wrote: post #27
frud wrote: post #17

I can't wrap my head around this story. What does it mean in thermodynamic terms? Isn't there a fixed amount of energy per mass that it takes to convert liquid water into vapor? Why does it matter that the energy comes from light?

My 8th grade understanding is evaporation doesn't always mean steam.

Huh what? I thought steam === water vapor

Re: Light can make water evaporate without heat

#69

Post by tzot »

ethanbond wrote: post #26
frud wrote: post #17

I can't wrap my head around this story. What does it mean in thermodynamic terms? Isn't there a fixed amount of energy per mass that it takes to convert liquid water into vapor? Why does it matter that the energy comes from light?

> In recent years, some researchers have been puzzled upon finding that water in their experiments, which was held in a sponge-like material known as a hydrogel, was evaporating at a higher rate than could be explained by the amount of heat, or thermal energy, that the water was receiving. And the excess has been significant — a doubling, or even a tripling or more, of the theoretical maximum rate. Apparently it evap…

As I understand it, when you heat water, you give energy to all of the water molecules that start moving faster in their random direction. So molecules that were directed towards outside the water mass are “directly” extracted, and the rest will bounce around in the increasing pressure until they are “indirectly” extracted (I used “directly” and “indirectly” non-scientifically here, just to make a distinction.) It takes quite a lot of energy which leads to evaporation over time.

I think what they found is a set of circumstances where the energy of the light “chips off pieces” of water, so the energy needed is much less. A small broken-off “piece” (or cluster of water molecules) has a very large ratio of surface area over volume, so the rest of the evaporation is taken care of by the surrounding environment as-is.

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