The researchers say the effect can be substantial and call it ‘a major part of the picture’. Under the optimum conditions of color, angle, and polarization “the evaporation rate is four times the thermal limit.” It was reported last year but this paper was only accepted last month. That report said: ‘The phenomenon might play a role in the formation and evolution of fog and clouds, and thus would be important to incorporate into climate models to improve their accuracy, the researchers say.’ The best incident angle for the light is 45°, according to the pre-print.
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It’s the most fundamental of processes—the evaporation of water from the surfaces of oceans and lakes, the burning off of fog in the morning sun, and the drying of briny ponds that leaves solid salt behind, says Massachusetts Institute of Technology (MIT, via Phys.org).
Evaporation is all around us, and humans have been observing it and making use of it for as long as we have existed.
And yet, it turns out, we’ve been missing a major part of the picture all along.
In a series of painstakingly precise experiments, a team of researchers at MIT has demonstrated that heat isn’t alone in causing water to evaporate.
Light, striking the water’s surface where air and water meet, can break water molecules away and float them into the air, causing evaporation in the absence of any source of heat.
The astonishing new discovery could have a wide range of significant implications. It could help explain mysterious measurements over the years of how sunlight affects clouds, and therefore affect calculations of the effects of climate change on cloud cover and precipitation.
It could also lead to new ways of designing industrial processes such as solar-powered desalination or drying of materials.
The findings, and the many different lines of evidence that demonstrate the reality of the phenomenon and the details of how it works, are described today in the Proceedings of the National Academy of Sciences, in a paper by Carl Richard Soderberg Professor of Power Engineering Gang Chen, postdocs Guangxin Lv and Yaodong Tu, and graduate student James Zhang.
The authors say their study suggests that the effect should happen widely in nature—everywhere from clouds to fogs to the surfaces of oceans, soils, and plants—and that it could also lead to new practical applications, including in energy and clean water production.
Full article here.
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Image credit: Robert A. Rohde @ Wikipedia
Tallbloke's Talkshop 
What about wind?
WELL I guess so, right enough. from the workshop, welding is a great example throwing out so much light radiation, Guess its in the Farm yard nursery that we NEVER Learnt that aspect of physics ….. but then what about the urbanites and their great skools? Yeasssss, education… what else have we been taught and received great grades, yet Know NOTHING about the real worldly functions ?
Cold wind ? … agitation of the Seas, adds KE, + Spray Volumetric Surface Area, etc …… + Bright light Cloud disappearance on a spring morning around 10am up here. Isa fascinating observation when you have time, listening to the Lark playing over the frolicking Lammies and caffies, the disturbed Peewit and the Clang of the Horse rollers behind the TE-20 on the Crofter’s grass park, whilst auld Jeemie is gi’en the squeezebox a go.
Well that is surprising and very interesting.
Sounds very much like a “cold fusion” discovery. Latent heat of evaporation needs to come from somewhere.
Sounds like a refrigeration technique. If you can evaporate water with just 1/4 of the latent “heat of evaporation,” the other 3/4 must be cooling (removed heat), presumably cooling of the water.
This lacks an explanation:
‘the temperature rise shows strong incident angle dependence, peaking at ~45° under the TM-polarized laser beam; in contrast, the temperature rise is nearly zero at normal incidence. Fig. S2 shows power dependence of the temperature rise at 45° incident angle, which is approximately linear.’
https://arxiv.org/ftp/arxiv/papers/2310/2310.19832.pdf – [Fig. S2 is on p.57]
Re. last comment, Eurekalert’s article on the new paper says:
The effect is strongest when light hits the water surface at an angle of 45 degrees. It is also strongest with a certain type of polarization, called transverse magnetic polarization. And it peaks in green light — which, oddly, is the color for which water is most transparent and thus interacts the least.
Chen and his co-researchers have proposed a physical mechanism that can explain the angle and polarization dependence of the effect, showing that the photons of light can impart a net force on water molecules at the water surface that is sufficient to knock them loose from the body of water. But they cannot yet account for the color dependence, which they say will require further study. [bold added]
https://www.eurekalert.org/news-releases/1042442
Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves
https://en.wikipedia.org/wiki/Polarization_(waves)
Eurekalert also says:
Solving a cloud conundrum
The finding may solve an 80-year-old mystery in climate science. Measurements of how clouds absorb sunlight have often shown that they are absorbing more sunlight than conventional physics dictates possible. The additional evaporation caused by this effect could account for the longstanding discrepancy, which has been a subject of dispute since such measurements are difficult to make.
during sunrise on cloudless days, temperatures decrease noticeably (sensor located in 24h shadow), without creating fog, observed at my place, during the weeks of equinox …
Hmm. Personally I find the claims about light (no mass, only momentum thus a wave but also a particle…) to be obviously incoherent. How is light achieving this evaporation if it is a wave?
Light has no resting mass (in theory), but as it’s never at rest that can be ignored. Photon energy must have mass equivalence as per Einstein’s equation.
Rules of seawater reflectance say angle out = angle in, so ’45° in’ is the only angle that gives 90° total angle of in+out. Maybe that has some significance.
https://www.britannica.com/science/seawater/Optical-properties
We explained these observations by proposing that photons can directly cleave off water molecular clusters from the air-water interface without going through a photothermal process and call this effect the photomolecular effect, in analogy to the photoelectric effect discovered by Hertz (10) and explained by Einstein (11). [bold added]
https://arxiv.org/ftp/arxiv/papers/2310/2310.19832.pdf
Oldbrew, I know Einstein’s equations, hence the momentum point. But the claims about light fit the equations, not the other way around. What is a massless particle? Oh its a wave. How does a wave behave like a particle? Oh, it’s a particle too. Then how massless? Oh because it never stops because otherwise our equations are wrong. What happens to a photon at the end of the universe then? I suspect the reason we can’t amalgamate Einsteinian physics and quantum physics is that neither are quite right.
Maybe the definitions aren’t right but the effects can still be observed?
Had to bite.
Is this joke? I am confused by the simple lack of understanding here. Solar light enrgy heats the oceans directly by absorption without the need for “heat”, FFS. The earth cools by releasing photons of radiative energy, its the ONLY way cooling can happen.
The energy of light can be measured in joules and photon/wave energy can heat stuff directly.
1eV = 1.6×10^-12 Joules, right? A level physics basics.
Have no time to read the whole thing but the quote suggests its based on at least one false presumption by a numpty of the type that academe is now mostly full of..
PS Where does energy in a chemical reaction come from … answer is a mass loss which in fact is a change in the total electron binding energies involved and that also creates photons that heat stuff up per their enrgy measured by e=mc^2 Joules. Simples!
PPS Doesn’t everyone know that?
This little gadget seems to show that photons have kinetic energy.
https://en.wikipedia.org/wiki/Crookes_radiometer
Measurements of how clouds absorb sunlight have often shown that they are absorbing more sunlight than conventional physics dictates possible. The additional evaporation caused by this effect could account for the longstanding discrepancy, which has been a subject of dispute since such measurements are difficult to make.
Either this research offers an answer, or something else is needed.
More from the paper:
Liquid-water surface temperature response. We used an IR camera (Figs. 1b&1c) and a thermocouple (Fig. 1d) to measure the temperature response of the water surface induced by a green laser under different angles of incidence and polarizations (SM1.4&SM2, Table S1). Fig. 1b illustrates the water surface temperature response with time measured by the IR camera with the incident angle of 45° for both the transverse magnetic (TM) and transverse electrical (TE) polarized lasers. For the TM-polarized laser the water surface temperature increases by 0.7 °C in the first 30s after the laser turns on. It reaches a steady state with a rise of 0.95 °C after ~200 s. In contrast, the temperature rise under the TE-polarized laser is less than 0.3 °C. [bold added except heading]
https://arxiv.org/ftp/arxiv/papers/2310/2310.19832.pdf (see p.4)
“How light can vaporize water without the need for heat”
An observation based on Law. If energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another and the properties of light are both wave and particle then light is a form of energy. That being the case, then a photon of light is transferring energy to the water molecule. We call this heat transfer via radiation. This is not new or novel. Vaporization of water has its heat supplied by light. Energy = Heat
The observation that 45 degrees is the optimum angle of incidence for heat transfer via light is interesting when 90 degrees, i.e. directly overhead has always been presumed to be the optimum. Are we actually saying the orientation of water molecules in the atmosphere are mostly facing in one direction (not random) so when the sun is directly overhead the actual angle is not 90 degrees?
dscott8186 says: April 27, 2024 at 6:28 pm
The observation that 45 degrees is the optimum angle of incidence for heat transfer via light is interesting when 90 degrees, i.e. directly overhead has always been presumed to be the optimum.
The headline says ‘without the need for heat’. The paper calls it the Photomolecular Effect. MIT says:
In a series of painstakingly precise experiments, a team of researchers at MIT has demonstrated that heat isn’t alone in causing water to evaporate. Light, striking the water’s surface where air and water meet, can break water molecules away and float them into the air, causing evaporation in the absence of any source of heat.
https://news.mit.edu/2024/how-light-can-vaporize-water-without-heat-0423
The opening page of the 94 page paper summarises the findings, including:
(d) Temperature of the vapor phase becomes cooler under light illumination, and its distribution shows features different from thermal evaporation
MIT says:
Because the effect was so unexpected, the team worked to prove its existence with as many different lines of evidence as possible. In this study, they report 14 different kinds of tests and measurements they carried out to establish that water was indeed evaporating — that is, molecules of water were being knocked loose from the water’s surface and wafted into the air — due to the light alone, not by heat, which was long assumed to be the only mechanism involved.One key indicator, which showed up consistently in four different kinds of experiments under different conditions, was that as the water began to evaporate from a test container under visible light, the air temperature measured above the water’s surface cooled down and then leveled off, showing that thermal energy was not the driving force behind the effect.
https://news.mit.edu/2024/how-light-can-vaporize-water-without-heat-0423
“…showing that thermal energy was not the driving force behind the effect.“
So where does the latent heat of vapourisation come from?
The effect they observed is in addition to existing physics explanations. The study abstract says ‘We use over 10 different experiments to demonstrate the existence of this effect and its dependence on the wavelength, incident angle and polarization of visible light.’
Also: ‘Past cloud measurements have suggested significantly higher cloud absorptance than what existing models can predict (42-44), which had been subjected to questions due to difficulties in the experiment (45,46). The photomolecular effect and heating data we demonstrate here can provide both the theoretical basis and experimental support for increased solar radiation by clouds.’
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