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My name is David and I live in North Florida. I could use some help with information to help me with a project I have going. I am trying to construct a VERY efficient solar oven. The oven will mostly be comprised of three metal boxes of different sizes, one inside another, inside another. I intend to put them together in such a way so that the heat from the outermost box will be reflected toward the next box and the heat from that box will be reflected again toward the inmost box. I think this will concentrate the heat. The boxes will not directly touch each other. I plan to paint each box flat black on the outside and put reflective aluminum foil on the surface of the inside of each box. The question I have is this; since the inside of the boxes will be in the dark when the oven door is closed, will the heat still be reflected in such a way as to concentrate it toward the center, or does this type of reflective action have anything to do with heat created by light only? Does a reflective surface reflect heat even when there is no light involved? I would greatly appreciate any advice from someone who knows about thermodynamics. Thank you so much. Sincerely, David in Florida.
Question Date: 2018-05-11
Answer 1:

I suspect that your oven isn't going to work because of the second law of thermodynamics.

Reflective surfaces absorb less heat, it's true, but they also emit less heat. The way that solar cookers that I read about work is they reflect sunlight onto a target, and this reflected light turns to heat and does the cooking. This works because the high-temperature object being used to reflect light is the sun, so the maximum possible temperature is the temperature of the sun's photosphere. You could also make a solar oven with lenses instead of mirrors, like a giant magnifying glass.

In your case, what you are talking about building is essentially a greenhouse. The multilayered series of boxes would be great for storing heat, but I have a hard time believing that they will be able to concentrate it. You certainly will not be able to concentrate heat from just having the thing sitting around. I don't know what you'll be able to do with sunlight, but I doubt it will be an effective oven.

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