Fwd: OT: Items in a metal box are cooler?

Should work for beer too.

If John Doe isn't your name, why would you care if people insult John Doe?

It seems ironic that you would make a point of them posting under a fake name. Admittedly copying off-topic posts to other groups is rude.

Liar. Until recently you (or someone doing a good emulation of you) were defending your claims, not disclaiming them. I have not seen a clear retraction posted in this thread, just your blame claims (like this one i'm replying top).

Post the message-id or it didn't happen.

Stalker troll much.

that is undisputed, but you keep mentioning it.

Your lies will not be met with silence.

Neither with lies, yet you persist.

No, I have another metal box in the cellar for that, it gets to about

-20C. Not sure what that is in US standard arcane units, but cold enough to freeze the balls off a brass monkey anyway.

If you were seriously interested in doing something that would work and does not break the laws of thermodynamics there are now a handful of metamaterials that are essentially a mirror finish in visible and near IR and almost black in the thermal band for emitting.

In direct sunlight in a clear blue sky they can be 10C cooler than the air. 7C is more typical. I wonder how clean you need to keep them.

That is really funny coming from a self appointed netcop that does nothing but repost OT threads and headers into this group.

You ought to know.

If only that worked. Sets of boxes within boxes (IDK what they are called) are popular in India. You wouldn't even have to have them specially made. :-)

A traditional way of cooling water in hotter climates is to put it in earthen jugs. Water seeps out invisibly through microscopic pores on the walls and cools by evaporation.

I have one of those too, and another one where it's sometimes much much warmer than ambient, but weirdly it doesn't do it all the time. (More often in cooler weather, I notice.)

The really mysterious one is this metal cup I'm drinking from right now.

"It's the greatest invention in the world! It keeps hot things hot and cold things cold!...how _do_ it know?"

Cheers

Phil Hobbs

Negative emissivity, of course.

I you built a good reflector (copper bowl, copperclad FR4, something like that) and put something at the focal point, and point it at the sky at night, I wonder how cold you could make the thing.

Tall parabolic shape maybe, the opposite of a solar furnace.

This would obviously be a little bit of free energy.

torsdag den 6. august 2020 kl. 22.57.10 UTC+2 skrev John Larkin:

I don't see how a reflector is going to help make something cold

Tnere's no need of focus, just a sunshield and insulation will do it. Works best in vacuum. Ideally, you'd have several layers of shield at successively lower temperatures, and site the object near one of Luna's poles.

It has been patented, I believe.

As far as 'free energy' goes, it still has the limitation of shedding heat only at the rate set by its blackness and temperature to the fourth power... so it cools non-hot objects slowly.

If you want to try it a shallow polished metal dish just big enough to hide the ground from another shallow unglazed clay dish on expanded polystyrene is the way to do it. Thin layer of water in the clay dish.

Egyptian technology that could make ice in the desert on a good clear night by a combination of wind chill and radiative cooling. They would have used straw to isolate it from the warm ground.

Observatories these days go out of their way to make the domes stay neutral at night now that we have air conditioning plant to keep the interior daytime temperature under control.

In the old days they used the whitest of white paints to keep the solar heat out but then suffered badly from dome seeing as night progressed and cold air formed turbulent streams falling in off the dome.

The object would need to not see anything warm, like the ground, or a low-angle peek at the atmosphere where the path through air and clouds and dust is long. It needs to see just clear space.

Luna would be hotter than deep space. Don't let it see the moon.

Space has a radiative temperature of a few K. A blackbody way out in space will eventually get that cold. On Earth, we'd need it to think it's in space, namely all that it sees in all directions looks like space. We wouldn't want it to be exposed to anything warm, like the ground.

A deep gold-plated parabola would be good, aiming at the sky.

It would be surrounded by the reflection of the sky. The mirror doesn't emit much itself so the heat from the object at the focal point would radiate in all directions into space.

I've measured the temperature of space on a clear night and gotten temps around -50C. I think more than once it was so cold the device displayed an error. No wonder North Dakota is so cold. They get lots of clear nights.

fredag den 7. august 2020 kl. 00.29.12 UTC+2 skrev John Larkin:

but that only takes care of radiation, so unless the thing you are trying to cool is perfectly insulated like in the vacuum of space ...

than

Thin walled SS is a pretty good metallic insulator. Silver plated glass (or some such) was the first Dewar. :^) George H.

I never heard of the Eygptian approach.

At radar frequencies, the temperature of the sky is 50 K (degrees Kelvin, not Centigrade), but don't look at the Sun or the Moon.

For comparison, molecular Nitrogen boils at 77 K.

Joe Gwinn