What Causes High Heat Loss in Space?

[puhlonker]

in the movie i was watching that is set in space, some of the characters get frozen while exposed to the vacuum of space without being properly insulated. Now i am wondering is my understanding of heat energy incorrect.

I thought heat would be taken from the body by every atom that interacts with it. and the more atoms/molecules that take the energy the quicker the heat is lost. (ie air turbulence increases heat loss). in space there are very few particles to interact with the body inquestion. i remember hearing a figure for how little atoms there are in a metre cubed of space(in space). . . can't remember what it was, but i it was an incredibly small number.

what is it that would allow for such a high rate of heat loss in space? am i missing something? or have i just learned a model for heat transfer that doesn't apply here.

and there was me thinking that a vacuum was the best insulator?

as i think about this
if steam would freeze and turn to ice in such conditions, using PV=nRT would imply as the pressure drops something on the other side must drop too, in this case T. is that reasoning correct. if so, where does the energy go? if its not taken away by other atoms? it can't travel as electromagnetic energy?

 

[androidx219]

I don't think that anybody would suddenly freeze if exposed to vacuum and you are right that vacuum is the best insulator. The only method of heat transfer from the body to outer space is radiation in this case as there are no atoms for conduction or convection. The heat transfer in the form of radiation is proportional to fourth power of temperature that means if the temperature of the body is sufficiently high, the radiative heat transfer would be much higher (also depends on the value of the constant of emissivity if i remember correctly). And the energy does go in the form of electromagnetic energy (radiation = electromagnetic energy).

 

[JaredJames]

Sounds like you were watching Sunshine.

No, you won't freeze that quickly in space - it's going to be one of your lesser concerns at that point.

A vacuum is a very good insulator.

 

[Dale]

Vacuum is a good insulator, but outer space is also very very cold. That means that, although the heat transfer may take quite some time, the equilibrium temperature you will eventually reach is quite close to absolute 0.

Here is an old thread on the topic:

https://www.physicsforums.com/showthread.php?t=189322

 

[Bill_K]

Just being exposed to vacuum won't cause you to freeze, however if the scene you were watching was an explosive decompression, such as an air lock being suddenly opened, well...

Air from your lungs will suddenly expand. Plus any moisture from eyes, nose, mouth will quickly evaporate. Both of these will have a temperature-lowering effect. Suggest you keep the door closed.

 

[russ_watters]

Vacuum is a good insulator, but outer space is also very very cold. That means that, although the heat transfer may take quite some time, the equilibrium temperature you will eventually reach is quite close to absolute 0.

Note that because there is no air, it is a good insulator for conduction and convection, but it is also almost perfectly "uninsulated" for the other means of heat transfer: radiation. And radiation is a surprisingly efficient and substantial means of heat transfer. So objects in space will radiate their heat away surprisingly fast if not insulated against radiative heat transfer - and if not pointed at the sun...though you can get very cold on one side and very hot on the other pretty quick (see: the Moon).

 

[Drakkith]

One of the main things in space suits is a cooling system to transport excess heat from the spacesuit and occupant. Same with satellites. They have several ways to shed excess heat or to insulate themselves if needed, depending on the conditions of the satellites orbit. (Such as taking it behind the Earth where it is dark.)

 

[Penn.6-5000]

At what rate do you radiate heat? The maximum emitted power is the Stefan-Boltzmann constant (5.67*10^-8 Watts per square meter per Kelvin^4) times the surface area of your body (Wikipedia gives an average of 1.73 square meters) times your skin's absolute temperature raised to the fourth power (your skin should be about 306 Kelvins) times a constant called the "emissivity" of your skin (about 0.566 for white people, according to http://www.rwc.uc.edu/koehler/biophys/8d.html ), so if I were naked in space I'd expect to lose body heat at a rate of 467 watts. This analysis covers radiation only and ignores the effects of evaporation pointed out by Bill_K.

 

[Dale]

That is about what I got in the older thread I linked to above.