Oh yeah, in fact you can put a metal box inside a metal box and get even more cooling. This can be continued ad infinitum. But you can't get down to absolute zero, that would violate laws of thermodynamics.
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Rick C.
- Get 1,000 miles of free Supercharging
Human senses are amazing, and one can pretty well estimate the thermal conductivity of a surface by touching it. Metal feels cooler than paper, even when both are settled at ambient.
Fingers are amazing at sensing textures, too.
Of course a metal box doesn't make itself cooler than a plastic one. That would violate COE and the box would get all drippy.
What "FACT" is this? Under what set of conditions do you believe it will be true?
In the general case, if a metal object is sitting in a room where the room temperature is stable, the metal object will come into thermal equilibrium with the rest of the room. They'll be at the same temperature. Heat energy will enter, and leave the metal object at the same rate. (If you want them to have different temperatures, you have to add work to the system to supply heat, or to "pump" it away somehow.)
If you touch the object then, it can quite easily _feel_ cooler than whatever it's sitting on, or cooler than the room air, even though they're at the same temperature. This has to do with the fact that your body's temperature is higher than the metal, and the metal will conduct energy away from you body faster than the air (or the table). As this happens, the metal will warm up to a higher temperature than the ambient, and if you've put something inside it, that object will also heat up.
Now, there are definitely conditions under which a metal object can _temporarily_ be cooler or hotter than the ambient air. For example, if you place a dark-colored metal object outdoors in the afternoon, and wait until the sun goes down and the sky becomes dark, the metal will cool down faster than the air does. This happens because it's an efficient radiator of infra-red, and radiates its internal heat away into the (dark) sky quite efficiently. The metal can drop well below the air temperature, and if it cools enough, water from the air will condense on its surface as dew.
The opposite thing happens in the morning, when the sun comes up - the metal will absorb sunlight efficiently and will heat up faster than the air does.
So, you can make a refrigerator of sorts - a well-insulated box with a set of heat-radiator fins on it. During the day, keep the box well-covered and insulated. When the sun goes down, remove the insulating cover, and let heat radiate away into the dark sky. Won't work as well if the sky is cloudy at night, though.
This trick doesn't require metal, of course. Solar pool-heating systems can be used to cool a pool by running water through the (plastic) panels at night - this is sometimes done in hot climates to provide a cooler pool during the day.
Polished metals, especially copper and brass, are excellent reflectors at thermal wavelengths. Plastics are nearly black in the thermal IR. So if there is a radiant heat source around, the metal will feel cooler than some other things.
If the metal is the radiant heat source, do I want to paint that metal black, or leave it bare, for cooling? I'm thinking of a motorcycle engine's air-cooled cylinder and head.
I've read inconclusive blather about black radiating more heat, but the paint also being an insulator.
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