I have a Hydro Flask thermos. It's friggin amazing. Keeps my coffee hot all day I think by surrounding the inner cylinder with an outer cylinder, and between the two cylinders (where the insulation would go) is a vacuum. I think that's how it works, and I think that's very cool.
But I remember Padme saying to that wiener Anakin that space is very cold. I guess I can see how that would be true, if by cold she means there aren't a lot of atoms capable of transferring heat via conductive and convective methods. Does "space" have a temperature?
Isn't the extension of that having space ships/ISS (in real life) that are forced to dump heat into space (somehow)? That is, if heat can't escape the interior shuttles because it can't conduce or convect out.... wouldn't it just increase until the internal temps were the same temp as the source of the heat?
I don't understand. I am obviously wrong. But what is correct?
Space doesn't really have a temperature. The random few gas particles in interstellar space may be either extremely cold or extremely hot but there just isn't much of them to transfer heat too or from.
There is a "soup" of low energy photons leftover from the Big Bang called the Cosmic Microwave Background. The temperature of those photons are very close to absolute zero as Charmonium pointed out. We see them everywhere so they are the closest thing to a temperature that space has.
Now let's do a little thermodynamics to answer your insulated cup question . There are three types of heat transfer.
- conduction - heat flow through a solid
- convection - heat flow into a fluid
- radiation - heat flow through a vacuum
If you've built a PC you are probably familiar with conduction and convection.
The CPU dumps its heat via conduction into the heat sink. The heat sink dumps its heat into the air via forced air convection through it's fan.
To compare these heat removal methods let's assume we've got a 1 m^2 by 1cm thick piece of copper. On one side we have 100C water like you might put in your thermos and on the other side it's 20C like the ambient air.
To calculate the amount of heat flow through conduction we use the following equation:
Q= E*Sigma*A(Th^4- Tl^4)
- Q is the heat flow in watts
- in W/mK) (400 for copper)
- A is the area - (1m^2 for our example)
- Th is the high temperature in C or K - (100C)
- Tl is the low temperature in C or K - (20c)
For our example that copper plate would transfer heat at a rate of
3,200,000Watts.
For convection:
Q= Hc A(Th- Tl)
- Q is the heat flow in watts
- Hc is the convective heat transfer coefficient for the fluid in W/m^2K- (25 for air at 20C and blowing at 5mph or so)
- A is the area - (1m^2 for our example)
- Th is the high temperature in C or K - (100C)
- Tl is the low temperature in C or K - (20c)
For our example that copper plate would transfer heat with a 20C breeze blowing over it at around
2,000W.
Finally let's look at radiation which would how the fluid in your vacuum flask loses heat from the interior to exterior wall.
Q= E*Sigma*A*(Th^4- Tl^4)
- Q is the heat flow in watts
- E is The emissivity of the material - (0.03 for polished copper)
- A is the area - (1m^2 for our example)
- Sigma is the Stefan-Boltzmann constant - 5.67x10^-8 W/m^2K^4
- Th is the high temperature in K - (100C - 373K)
- Tl is the low temperature in K - (20c - 293K)
Our copper plate would radiate at about
20W.
So it's easy to see that using a vacuum and low emissivity material makes a great insulated container. It conducts 100s and 1000's of times less heat.
That's actually a problem for a spacecraft like the ISS. We generate quite a bit of heat internally from crew and equipment. It would cook the inside of the station without heat exchangers and radiators to provide cooling.
To make the radiators work better than your thermos we use a high emissivity (closer to 1) material and our Tl is deep space which is -270C.
So instead of radiating 20W/m^2 like in our previous example we radiate at closer to 650W/m^2. Still not as good as convection or conduction but better.
Actually the ISS radiators are large enough that if we aren't careful they can freeze the internal water cooling loops. So we will angle the radiators at the Earth during the night passes instead of deep space.
So the ISS absorbs radiant heat, and gives off radiant heat? and that's how it balances it's temps? Interesting!
External active equipment on the ISS generally has insulation and heaters for the night passes and cold plates connected to the cooling loops for day passes or when powered.
Modules also have cooling loops and heaters to maintain temperature. Passive structures may have special coatings or insulation.
Temperatures can fluctuate a lot and so each part of the station has to be designed to either accept those fluctuations or mitigate them.
Twice a year the sun doesn't set for several days and we temperatures in the sun get very toasty while those in the shade get very cold.
There are special radiators on the ISS that shed the heat.
Liquid ammonia flows there those and sheds the heat as IR. ... and looks like someone is going to be doing a space walk to go fix that one.
Nah. It's been like that for years. The panel
is still held on well enough not to be a hazard and there's enough cooling margin that it hasn't affected operations.
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