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Your description does not appear to be correct. Ice is not being formed at the "focal point," ice is being formed under the reflector. You can't focus coldness
by SamBam 7y ago
Your description does not appear to be correct. Ice is not being formed at the "focal point," ice is being formed under the reflector.
You can't focus coldness. "Cold" radiation is simply less radiation. When you focus it, you get more radiation, not less of it. More radiation means more energy.
Instead you're simply seeing the effect of radiative cooling. See "Nocturnal ice making in Early India and Iran" [1]. By insulating the sides of a pan of water, and leaving the only window for radiation pointed to the night sky, you're ensuring that more radiation is leaving the water than entering it. Thus the water cools down.
So it would work equally with an insulated box with high walls. It's not about focusing the coldness.
[1] https://en.wikipedia.org/wiki/Radiative_cooling#Nocturnal_ice_making_in_Early_India_and_Iran https://en.wikipedia.org/wiki/Radiative_cooling#Nocturnal_ic...
- ColinWright 7y agoI have a feeling we're talking past each other, and I'm not going to bother addressing everything you've said point-by-point. Experiments show that have a parabolic reflector configured correctly results in a stronger effect. You're not focusing coldness, but the radiation from the body being cooled emerges in every direction, so putting it at a parabolic focus ensures that all the radiated heat gets directed outwards to the night sky. Yes, simply having an insulated container and having an opening pointing at the sky does work, but it's not the best you can do.
- likpok 7y agoThe focusing effect will help, because you're focusing the infrared radiation from the object away. If you have an insulated box with tall sides, radiation from the object will reflect from the sides of the box back to it, keeping it warm (or less cold).