Cooler objects able to increase the temperature of warmer objects?

[berkeman]

I've read about devices that direct IR radiation from objects to the night sky which is effectively a radiator to space though not as effective as actually being in space. You can make ice even when the ambient air is in the 50's F. Cleverly designed systems may be able to convert the IR radiation of the Earth or of solar warmed objects such as rooftops to useful energy by passive radiation to space as the cold sink. The Earth typically radiates over 300 W/m^2 at night. Of course doing all that may not be worth the cost and complexity.

At least the last part of your post is incorrect, I believe. Do you have links to the other assertions in your post?

It looks like you are confusing the reflective albedo of the Earth during the daytime (when insolation is around 1kW/m^2) and the much lower radiation during the night...

from -- http://eesc.columbia.edu/courses/ees/climate/lectures/radiation/

The Earth's albedo.

The Earth's surface reflects (that is, returns the radiation back to space in more or less the same spectrum) part of the solar energy. This is what makes the part of the Earth lit by the sun visible from space (Figure 8) in the same way that the moon and the other members of the solar system are visible to us, despite their lack of an inner source of visible radiation. The most obvious aspect of Figure 8 is the brightness of the Earth's cloud cover. A significant part of the Earth's reflectivity can be attributed to clouds (this is but one reason why they are so important in the Earth's climate). In climate texts the reflectivity of a planet is referred to as the albedo (that is, albedo = reflectivity) and is expressed as a fraction. The albedo of Earth depends on the geographical location, surface properties, and the weather (can you tell from Figure 7 which has higher albedo, the land or the ocean?). On the average however, the Earth's albedo is about 0.3. This fraction of incoming radiation is reflected back into space. The other 0.7 part of the incoming solar radiation is absorbed by our planet.

 

[itfitmewelltoo]

I am wondering if the question is appropriately termed "thermodynamics". The problem is really a quantum dynamics issue. Thermodynamics is a mass matter theory and applies to steam, refrigerants, etc. It changed to statistical mechanics after Einstein's paper on Brownian motion. There is some confusion that arises from over applying the 4 laws of thermodynamics. It's a bit of a context problem. Thermo just doesn't really apply to pure IR problems. But without the context of experiment and application, without the historical context, or the context of having taken one course in thermodynamics, another in quantum mechanics, and a third in electro-dynamics, it is easy to see how they get convoluted when trying to learn it on the internet.

 

[Dale]

I've read about devices that direct IR radiation from objects to the night sky which is effectively a radiator to space though not as effective as actually being in space. You can make ice even when the ambient air is in the 50's F.

I have not heard of one that is that effective, but I have heard of this approach in general:

https://news.stanford.edu/news/2014/november/radiative-cooling-mirror-112614.html

 

[bob012345]

At least the last part of your post is incorrect, I believe. Do you have links to the other assertions in your post?

It looks like you are confusing the reflective albedo of the Earth during the daytime (when insolation is around 1kW/m^2) and the much lower radiation during the night...

from -- http://eesc.columbia.edu/courses/ees/climate/lectures/radiation/

The Earth is a blackbody at night radiating to space or at least the surface radiates to the atmosphere which radiates to space and to the surface. I wasn't confusing the nighttime radiated power with the daytime albedo. If the surface temp is say 20C and the emissivity is say 0.9, one can compute the radiated power. As an aside, I believe panels that effectively absorb IR radiation in low Earth orbit at night would be able to use that power also if they effectively coupled to the dark sky as the cold sink. Regarding the cooling, here is a link;

https://en.m.wikipedia.org/wiki/Radiative_cooling

 

[berkeman]

e Earth is a blackbody at night radiating to space or at least the surface radiates to the atmosphere which radiates to space and to the surface. I wasn't confusing the nighttime radiated power with the daytime albedo. If the surface temp is say 20C and the emissivity is say 0.9, one can compute the radiated power.

Can you show that calculation? Or otherwise show where you got the 300W/m^2 number that you posted?

 

[bob012345]

Can you show that calculation? Or otherwise show where you got the 300W/m^2 number that you posted?

Assuming 20C surface temperature and an emissivity of around .9, that's 293K so using the Stephan Boltzmann law we have

8.67 10^-8 W/(m^2 K^4) * 293K^4 * 0.9 which is about 376 W/m^2 which is over the 300 W/m^2 number which was an estimate of the average.