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Will Barite save the world?
  
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bob kerr




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PostPosted: Sep 23, 2021 12:13    Post subject: Will Barite save the world?  

The Mech Eng department at Purdue University has developed a paint so white that it reflects more light energy than it absorbs essentially cooling the surface below. It could replace AC especially in Tucson!!

The magic ingredient? Barite!

search - "Purdue paint" to see various articles.

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lluis




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PostPosted: Sep 23, 2021 14:32    Post subject: Re: Will Barite save the world?  

Just curiosity....

If I do not understand bad thermodynamics, you could not send out more than you get...
Maybe just a misunderstanding in article, maybe a misunderstanding by writers....
As it happened in "cold-fusion, that well, never happened.... :-(

With best wishes (in Facebook anyone could find tubes saying that continuous movement exists...)

Lluís
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bob kerr




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PostPosted: Sep 23, 2021 14:48    Post subject: Re: Will Barite save the world?  

it has to do with "black box cooling" - it radiates more than it absorbs so it essentially cools what is behind it.

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alfredo
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PostPosted: Sep 23, 2021 16:33    Post subject: Re: Will Barite save the world?  

That can only happen if the inside is hotter than the outside, then it can radiate more than it absorbs, so, if it is 40 degrees outside, the paint can't cool your home to below 40 degrees, otherwise, as Lluis pointed out, the laws of thermodynamics would be violated and the next thing we'll be hearing on the news is someone finally invented perpetual motion machines ;)) ... A misunderstanding on the part of the journalist, I suppose. Anyway, in hot climates this paint won't kill the market for air conditioners.
A pity, because the village where I'm currently residing in Catalonia has a dozen old abandoned barite mines. And coincidentally the village where I used to live in Bolivia had several abandoned barite mines too.
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John Hodgson




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PostPosted: Sep 23, 2021 19:04    Post subject: Re: Will Barite save the world?  

The article was very misleading. Even if the paint was white, how long would it remain white on a roof or side of a building?
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bob kerr




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PostPosted: Sep 23, 2021 20:42    Post subject: Re: Will Barite save the world?  

don't confuse thermal heat transfer with radiative heat transfer (black body or black box or daytime sub-ambient radiative cooling). the physics is well beyond what we need to discuss here but the technical paper written by Xiangyu Li (Ultrawhite BaSO4 Paints and Films for Remarkable Daytime Subambient Radiative Cooling) should be looked at if interested.

abstract follows

bob


Radiative cooling is a passive cooling technology that offers great promises to reduce space cooling cost, combat the urban island effect, and alleviate the global warming. To achieve passive daytime radiative cooling, current state-of-the-art solutions often utilize complicated multilayer structures or a reflective metal layer, limiting their applications in many fields. Attempts have been made to achieve passive daytime radiative cooling with single-layer paints, but they often require a thick coating or show partial daytime cooling. In this work, we experimentally demonstrate remarkable full-daytime subambient cooling performance with both BaSO4 nanoparticle films and BaSO4 nanocomposite paints. BaSO4 has a high electron band gap for low solar absorptance and phonon resonance at 9 μm for high sky window emissivity. With an appropriate particle size and a broad particle size distribution, the BaSO4 nanoparticle film reaches an ultrahigh solar reflectance of 97.6% and a high sky window emissivity of 0.96. During field tests, the BaSO4 film stays more than 4.5 °C below ambient temperature or achieves an average cooling power of 117 W/m2. The BaSO4-acrylic paint is developed with a 60% volume concentration to enhance the reliability in outdoor applications, achieving a solar reflectance of 98.1% and a sky window emissivity of 0.95. Field tests indicate similar cooling performance to the BaSO4 films. Overall, our BaSO4-acrylic paint shows a standard figure of merit of 0.77, which is among the highest of radiative cooling solutions while providing great reliability, convenient paint form, ease of use, and compatibility with the commercial paint fabrication process.
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lluis




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PostPosted: Sep 24, 2021 08:25    Post subject: Re: Will Barite save the world?  

There is any difference in thermal heat transfer and radiative heat transfer?
It is just heat transfer,
To have such transfer, there should be a gradient: in otherer words. there should be a transference from from hotter to cooler.
If they say opposite, well, there is full of people saying that Earth is flat (of course! If not, we would fall out of it!), and that continuous movement exists...
And of course, thermodynamics is just a plain lie....

All in all, looks to me as a famous (among chemists....) article published in Tetrahedron Letters, a very well known and highly reliable scientific magazine, peer reviewed, in which, many years ago (around 50), when quiral synthesis was in vogue, saying that when doing a reaction of so and so, with magnetic stirrer turning to left, an excess of x% of an enantiomer was reached (x% is a very small figure, less than 1%). When same reaction was done using magnetic stirrer turning to right, an excess of y% of the opposite enantiomer was got.

In next number, a short article, saying that next time author of the "interesting article" should be aware that the enantiomeric excesses he mentioned were "ç*below the accuracy* of device employed to measure them....

As Alfredo said, a body could not radiate more energy than the one it receives, unless environment is cooler than it...
And a quiz.... : if you have a freezer, with open doors in a room, the temperature of room will rise or will get down?

With best wishes

Lluís
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Amir Akhavan




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PostPosted: Sep 24, 2021 08:27    Post subject: Re: Will Barite save the world?  

What the paper suggest is to be expected and perfectly in line with thermodynamics.

Thermodynamics only forbids the heat transfer to a warmer body.
This is not what happens here.

Consider Earth during day and night:

In daytime, sunlight (yellow) passes through the air, gets partially absorbed at the surface and converted to heat, rising the temperature of the surface.
Infrared radiation (red) with a waveleght corresponding to the surface temperature will be irradiated through the atmosphere into space.
At night, the surface continues to radiate IR into space, and the surface gradually gets colder.

The air is mostly heated up by conductive transfer of heat, not by the sunlight, and also not by the IR in the sun's radiation.
However, the conductive heat transfer from the surface to the air is very slow.



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Amir Akhavan




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PostPosted: Sep 24, 2021 08:30    Post subject: Re: Will Barite save the world?  

That's why the temeprature gradient in the atmosphere gets reversed at night.
At night, there's only radiative cooling, no sunlight to compensate for the heat loss.



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Amir Akhavan




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PostPosted: Sep 24, 2021 08:38    Post subject: Re: Will Barite save the world?  

So when you have two blocks of some material attached, thermodynamics forbids that there's a net heat transferred from one to the other, regardless of the materials.
That's because conductiuon and irradiation will send energy back and forth between them.

But if one of the materials does not absorb IR radiation, any IR radiation produced by a body will just pass through it into space, just like on Earth, and the temperature of one body can very well drop below that of the other.

Conditions to be met for this to work:
IR irradiated from one body must not be absorbed by the other and just pass through it.
Conductive heat transfer must be very low.

So the trick is to create a paint that casts a shadow on the material and permits IR radiation from the body through it.

This is improtant to understand, because this is what is behind climate change:
O2 and N2 do not absorb IR, but H2O, CH4 and CO2 do, and the amount of IR passed through the atmosphere to space is decreased by adding CO2



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PostPosted: Sep 24, 2021 08:53    Post subject: Re: Will Barite save the world?  

Like Lluis and Alfredo, my first impression was that this sounds like snake oil. But the authors are at good universities (MIT and Purdue) and the paper was published in a good peer-reviewed journal. I know that there is a lot of crap that gets published, but a criticism like this violating simple thermodynamics is something that i expect the reviewers would have caught.

As a thought experiment, if something could reflect all the radiation from the sun, it would cool a surface because some IR would still radiate out to space. If the wavelength of the black body radiation was such that it maximized the amount of radiation that could pass through the atmosphere, the cooling effect would be maximized (perhaps this is what they mean by "sky window emissivity"). Now of course nothing can reflect all solar radiation, but if it can reflect enough perhaps this can work.

This all said, even if real, i doubt that the effect would be enough to eliminate the need for A/C in Tucson. You will still be surrounded by hot air and other IR emitters which will heat a structure.
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Pete Richards
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PostPosted: Sep 24, 2021 08:56    Post subject: Re: Will Barite save the world?  

Thanks to Amir for his good and well illustrated explanation!

I think the problem in the original statement is that the paint would COOL the pavement (or whatever). I suggest this is not accurate. What might be accurate is that the paint would prevent what is underneath from heating up as much as the surrounding unpainted area, in the presence of an energy source such as sunlight. It would keep the underneath cooler, but it would not actually cool it off. What happens at night in the absence of solar input is a different question.

To bring this back to minerals, sort of, the same principles are important in the development and maintenance of glaciers and ice sheets during glacial episodes, because of the high albedo (reflectance) of snow. Snow is ice, which is a hexagonal mineral (uniaxial positive, a=4.498, c=7.338Å - temperature and pressure not specified).

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PostPosted: Sep 24, 2021 10:26    Post subject: Re: Will Barite save the world?  

Hi, Matt

Tetrahedron Letters was even more highly regarded than MIT. More or less. God's word in chemistry! And peer reviewed by top people.
And they published said fake report... (with an infantile error than even a mid educated one could fit at first view!)
Humans are humans, and humans, well, err.... :-(
As was the case of cold fusion... that ended as been a collection of wishes and misunderstandings and plain lies..

Gosh, if even revered Mendel did some (maybe more than some...) lies in his original report...
And he was right... Which I think is not the case in this case....

But anyway, a chaqun sélon son goût... (to each one, its own... From Fledemaus, Austrian opereta that I like a lot.... :-) )

With best wishes

Lluís
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James Catmur
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PostPosted: Sep 24, 2021 12:13    Post subject: Re: Will Barite save the world?  

Look at James Clerk Maxwell's demon - he tried to do the impossible in that thought experiment.
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John Hodgson




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PostPosted: Sep 25, 2021 09:19    Post subject: Re: Will Barite save the world?  

John Hodgson wrote:
The article was very misleading. Even if the paint was white, how long would it remain white on a roof or side of a building?

Sorry, I should have explained that the article I was referring to was published in the Smithsonian magazine titled, This Ultral-White Paint May Someday Replace Air Conditioning.
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bob kerr




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PostPosted: Sep 30, 2021 13:00    Post subject: Re: Will Barite save the world?  

there's a terrific YouTube channel I subscribe to: "Undecided with Matt Ferrell" and his most recent post talks about this radiative cooling - the physics, the implementation, the economics and the companies currently in the game.

you can find it searching YouTube for his channel or:

youtube dot com slash watch?v=pq8xDXkbXZs

this entire topic may not be specifically about minerals but it is certainly of interest to many of us - and an appropriate "Off-Topic" topic.

bob
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