>> In tests, it cooled surfaces by 4.5C below the ambient temperature, even in strong sunlight. I am not in phisics but AFAIU in order to "cool" one have to remove energy from the object being cooled. So the paint would have to actively emitt energy and well the best emitters are not while, are they? Perfect black body comes to mind but this probably would not work well in direct sunlight?
So can you explain the process by which the white paint is able to cool below ambient? Is this Maxwell's demon then;-)?
>> In tests, it cooled surfaces by 4.5C below the ambient temperature, even in strong sunlight.
I am not in phisics but AFAIU in order to "cool" one have to remove energy from the object being cooled. So the paint would have to actively emitt energy and well the best emitters are not while, are they? Perfect black body comes to mind but this probably would not work well in direct sunlight?
So can you explain the process by which the white paint is able to cool below ambient? Is this Maxwell's demon then;-)?
Everything else is absorbing more energy and getting hotter. This object isn't, so doesn't.
If that's the definition they use it starts to sound like an alternative truth.
We did this little experiment in elementary school, where we would take two jars filled with water and screwed tight. One of the jars was painted black, the other was covered in aluminum foil and then we put it out in the sun for a couple of hours.
After that we opened it and measured the temperature. But the way we learned it was that the jar with the darker coat absorbed more of the sun's energy and therefore got warmer. They
That would be my undrestanding - a black body will absorb EM energy from the outside well and also emitt some EM as well. The ratio of absorb/emit is dependent on "temperatures" of the EM radiation and the object.
Here we have a white body, in order to reflect the solar radiation (kinda definiton of 'white'), but also not reflecting the radiation from the object that it is covering and in fact somehow "sucking" out energy from it and emitting to the outside. So it would follow that the paint is "directional"
We don't know any mechanism that can convert long wavelengths into short wavelengths without needing additional energy.
For example if we could use frequency doubling on far IR to create even something like near IR we could then use photovoltaics to turn waste heat into useful electrical energy again, which would come pretty close to perpetual motion and would solve a lot of our energy problems.
Now I'm not one of those skeptics who watches a video on youtube seeing some guy pouring water into a container
Not getting hotter is not what they claim. The claim is "getting colder than ambient", even in full sun. I suppose the interpretation here is "getting hotter slower then ambient is" and not that it is actually making things cold. Do nothing special here just a strongly reflecing paint and twisted marketing.
But that still does not mean a sun-lit roof stays "below ambient temperature" during the day. Radiation cooling can work at night, this has been subject to research before - https://www.sciencedirect.com/... [sciencedirect.com] - but during the day it is still much more efficient to insulate your building from the hot surface of the root if you want to keep the building cool.
So can you explain the process by which the white paint is able to cool below ambient? Is this Maxwell's demon then;-)?
Thermodynamically, any surface that is poor at absorbing light will also be poor at emitting it. But that can still vary by wavelength.
The paint is highly reflective in visible and UV light. But not IR. It will absorb IR and also emit IR.
Sunlight is mostly visible light, which is reflected. Ambient heat is mostly IR, which is emitted. So the net result is cooling below the ambient temperature of other surfaces.
it..cools? (Score:3)
>> In tests, it cooled surfaces by 4.5C below the ambient temperature, even in strong sunlight.
I am not in phisics but AFAIU in order to "cool" one have to remove energy from the object being cooled. So the paint would have to actively emitt energy and well the best emitters are not while, are they? Perfect black body comes to mind but this probably would not work well in direct sunlight?
So can you explain the process by which the white paint is able to cool below ambient? Is this Maxwell's demon then ;-)?
Re: (Score:2)
>> In tests, it cooled surfaces by 4.5C below the ambient temperature, even in strong sunlight. I am not in phisics but AFAIU in order to "cool" one have to remove energy from the object being cooled. So the paint would have to actively emitt energy and well the best emitters are not while, are they? Perfect black body comes to mind but this probably would not work well in direct sunlight?
So can you explain the process by which the white paint is able to cool below ambient? Is this Maxwell's demon then ;-)?
Everything else is absorbing more energy and getting hotter. This object isn't, so doesn't.
Re: (Score:2)
We did this little experiment in elementary school, where we would take two jars filled with water and screwed tight. One of the jars was painted black, the other was covered in aluminum foil and then we put it out in the sun for a couple of hours.
After that we opened it and measured the temperature. But the way we learned it was that the jar with the darker coat absorbed more of the sun's energy and therefore got warmer. They
Re: (Score:2)
That would be my undrestanding - a black body will absorb EM energy from the outside well and also emitt some EM as well. The ratio of absorb/emit is dependent on "temperatures" of the EM radiation and the object.
Here we have a white body, in order to reflect the solar radiation (kinda definiton of 'white'), but also not reflecting the radiation from the object that it is covering and in fact somehow "sucking" out energy from it and emitting to the outside. So it would follow that the paint is "directional"
Re: (Score:2)
For example if we could use frequency doubling on far IR to create even something like near IR we could then use photovoltaics to turn waste heat into useful electrical energy again, which would come pretty close to perpetual motion and would solve a lot of our energy problems.
Now I'm not one of those skeptics who watches a video on youtube seeing some guy pouring water into a container
Re: it..cools? (Score:3)
Not getting hotter is not what they claim. The claim is "getting colder than ambient", even in full sun. I suppose the interpretation here is "getting hotter slower then ambient is" and not that it is actually making things cold. Do nothing special here just a strongly reflecing paint and twisted marketing.
Re: (Score:2)
The claim is "getting colder than ambient"
In the words of a know-nothing "science reporter".
Re:it..cools? (Score:5, Informative)
It radiates mid IR that goes through the atmosphere and into space.
Like: https://www.goodnewsnetwork.or... [goodnewsnetwork.org]
Re: (Score:2)
Re: it..cools? (Score:2)
Convective heat loss exceeds heat gained from direct illumination? Literally not rocket science.
Re:it..cools? (Score:5, Interesting)
So can you explain the process by which the white paint is able to cool below ambient? Is this Maxwell's demon then ;-)?
Thermodynamically, any surface that is poor at absorbing light will also be poor at emitting it. But that can still vary by wavelength.
The paint is highly reflective in visible and UV light. But not IR. It will absorb IR and also emit IR.
Sunlight is mostly visible light, which is reflected. Ambient heat is mostly IR, which is emitted. So the net result is cooling below the ambient temperature of other surfaces.