# How does Cooling work in Vacuum, with no surrounding Air ?

I want to wrap my head around this issue that popped up recently:

Satellites are tested on earth in "Thermal Vacuum Chambers". I can understand heating; Heating elements (not touching the satellite) emit infra red energy which is absorbed by the satellite, and it is heated up that way.

For cooling, intuitively I thought since there is no air inside the vacuum chamber to transmit the temperature via convection, any "cold object" not touching the satellite will not work.

Apparently it does work that way.

I can understand that any object above 0 degrees Kelvin will emit radiation. So an object with no surrounding air to keep it warm, will want to approach zero kelvin.

But how does having a cooling element near, but not touching, the satellite in vacuum, help it cool down ?!

Relevance

Think about most processes in physics, they are symmetric! So if an object can be heated by absorbing EM radiation, it can be cooled by releasing it. It's called Plank's law.

http://scienceworld.wolfram.com/physics/BlackbodyR...

The rate at which an object heats up or cools down due to radiation is a function of it's surroundings. Because the net rate of cooling is the difference between the radiation to the environment and the heating due to radiation from the environment. If a cooling element is nearby, the cooling element will absorb the radiation from the satellite without sending much back, thus speeding the cooling process. If there was a red hot piece of iron nearby, the iron might be sending more radiation to the satellite than the satellite was sending to the iron, so the iron would cool and the satellite would heat up. All objects emit radiation, the hotter the more.

• 2n2222
Lv 6

The satellite sits in a vacuum chamber. Some of the IR energy it radiates might or might not be reflected back. But if there's a cold-sink nearby, whatever energy goes into that won't be reflected back.

That's about as good as I can do here. There's a similar problem involving two concave parabolic mirrors that point at each other across the room. When you put a heat source at the focus of one, you'll get a hot spot at the focus of the other, which is fine. But it also turns out that if you put an ice cube at the focus of one, you'll get a cold spot at the focus of the other, which seems intuitive but doesn't make any sense at all in terms of how one normally thinks about waves.

• eddi
Lv 4
5 years ago

A clay jar. i'm afraid i will not inform you the chemistry behind it, I in simple terms comprehend that clay jars were used all through heritage as they retain water cool. Plastic, on the different hand, for sure does no longer. i comprehend that a minimum of area of it has to do with condensation on a clay jar, yet that is about my reduce. i ought to imagine it also has something to do with the actual undeniable truth that straightforward, and therefore warmth, can bypass properly through plastic, yet can't bypass properly through clay. Sorry to no longer be of more beneficial help.