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[Drake]

How exactly does it work in a space based vessel?

In modern day system/engine cooling its either air or liquid cooling.
  You either have cool(er) air passing around or through the hot mechanics which then travels through ducts or piping and is released into the atmosphere where the outer temperature equalizes the exhaust cooling it.
  The other way is you have liquid passing in and around the hot mechanics via tubing that then passes through a cooler that draws out the heat and sends it back towards the mechanics.

  Soo hows it work in spaceships? Some ships have large external vents but that would make you think they air cool their engines, but there is no air in space so what are they using some sort of vacuum cooling system or are they constantly pumping huge amounts of air out of their ships?
  I can't see how the first works, doesn't matter how 'cold' space is, with a medium to transfer the heat bugger all is going to happen. And I can't see the second being true as even the smaller end ships have month long supply stats, their no way they could fit all the air inside them.

 So if its not air cooling it would be liquid cooling, but then what are the exhaust vents for?

  My engine room needs your techy wisdom.

[LBraden]

Think of the BMW boxer engine, all the fins on it, that is what you are seeing, the vacuum of space cools the liquid (and we already have a tank for liquid cooling) that is pumped round the engine to keep it cool

[VOID]

Vacuum does not cool anything really well. Vacuum is an isolator.

Of course space is usually not a perfect vacuum and it doesn't make heat radiation totally impossible. Otherwise, all the suns would be in trouble doing their shiny sun thingy.

In fact, getting rid of heat is still a very big problem for any spaceship, which is why many ships in Star Wars have relatively large and many heat radiator surfaces.

How cooling systems work depends on the technology that is used. I usually use liquid-based fin-radiators in my designs. So the heat is picked up using a conductor fluid, then pumped through the fin radiator to cool down as much as possible. For short durations and increased heat production, there are also chemical cooling systems and the fin radiators can (and should) be supported by mist injectors. Water surprisingly does a good job at that. Spray it on your heat radiator and it helps you a lot getting rid of heat. Even in vacuum.

[Chrome]

Vacuum does not cool anything really well. Vacuum is an isolator.

I think you meant insulator, but in any case, no, exposure to the vacuum of space cools things very very quickly indeed. The mechanism is thermal radiation - IR propagates in a vacuum just dandy, it does not need a medium to propagate in. Stars work in exactly the same way; infrared, just like the rest of the EMS, heats things up, and it does not require anything to pass on the energy - it just RADIATES.

If you fall out of a space ship, you body temperature is likely to be somewhere around 37c, or 310k. Space is more or less at 0k which means there's a pretty big thermal discrepancy. Equilibrium dictates that the balance will be restored, and your body will begin to radiate thermal energy at a frightening rate - the rate determined by the difference in temperatures, so the closer your body gets to 0k the slower the rate. If you did step off a space craft naked, you would be frozen solid within a matter of, at best, minutes. More likely seconds.

In fact, getting rid of heat is still a very big problem for any spaceship, which is why many ships in Star Wars have relatively large and many heat radiator surfaces.

Uh, no, losing heat is space is fairly easy. If it were not, you'd see all kinds of interesting systems on things like Skylab and the ISS to do the job. Staying warm is, in fact, much more of a problem.

I think perhaps people here are forgetting the undeniable fact that heat dissipates perfectly well as radiation - it does so regardless of whether it is in a medium or a vacuum.

[Klick]

The devil is in the details here.  The deciding factor for whether space is effectively 'cold' or 'hot' (clumsy terms, I know) is at what rate an object radiates heat in deep space, and how this compares to heat loss rates under terrestrial conditions.

[Chrome]

The deciding factor for whether space is effectively 'cold' or 'hot' is at what rate an object radiates heat in deep space, and how this compares to heat loss rates under terrestrial conditions.

I think I know what you're getting at, but the engineer in me is feelin' repressed ;-)

Space is cold, it's very very cold. It is the coldest naturally occurring 'thing' in the entire universe, so cold in fact that it takes billions of dollars of investment to make anything colder.

However, since heat radiates in space (which was the main thing I was pointing out earlier) other sources of thermal energy also travel through it, hence a given object in space will cool at a rate determined by a variety of factors, but for the sake of simplicity, they mainly reduce to these;
A: The temperature of the object at 'point zero'.
B: The temperature of the environment at 'point zero' (In space this is as close to 0K as makes no real odds)
C: The amount of heat generated by the object.
D: The amount of heat acquired from other sources. (Stars, etc)
E: The emission characteristics of the object, which is a factor of material and surface area.

Two relevant factors to bear in mind here are that at our distance from the sun, the radiated thermal energy of the sun is virtually none - our planet is hot, comparatively, mainly due to the atmosphere and EM fields retaining the heat acquired since the creation of the system. Also, the frequency of radiated radiation is directly proportional to the energy being released; the hotter things get the further up the EM spectrum the emission, which roughly translates in practical terms to the ability to tell how hot something is by what colour it is glowing. Glow starts to kick it at around 750k, and progresses exponentially up the EM spectrum. There is some variations due to the material, but it's a fairly solid rule of thumb.

To gently slide back more firmly on topic - one has to bear in mind that SW ships usually operate in atmosphere as well as in space, so it is possible that what seem to be vents are just that, air cooling systems, but they aren't relevant in space.

However, a real world model for this would be that whatever it is you want to keep cold(er) on the ship would be connected to a heat sink of a highly conductive material. That heat sink would then connect (or simply be shaped as) a feature with a large surface area that is exposed to the extreme cold of space. The dissipation of heat energy from the heat sink drains the item in question because, as elementary physics dictates, the heat sink is 'trying' to reach an equilibrium with the surrounding environments - every watt of energy it absorbs from the item is then making it 'harder' to cool. The 'vent' areas may simply be the external heat sink's fins.

One thing we can say with fair certainty is that (assuming we're not going to discard real physics, which of course, you're welcome to do in a fantasy setting) since we've seen no evidence of vents or other things suggested to be radiator glow, then their temperature must be lower than around 750k. That gives you a rough baseline to calculate the actual amount of heat lost, which in turn could give you the theoretical maximum power output of the vessel in question. Mainly this was something I played with in reference to TIE fighters, but would also apply to other ships.

[Klick]

You know, those heat vents may actually be a secondary cooling mechanism; most of the ship's operational heat would be dissipated by dumping it into the outgoing exhaust particles, both increasing their energy (and thus the ship's thrust), and conveniently disposing of excess heat. We can get away with claiming a sizable amount of energy is dumped this way because, unlike the non-glowing radiator structures we see, the brightly glowing exhaust can have a much higher temperature.

And now for a long post full of science and math:

Assuming the Wikipedia articles on Black bodies and the Stefan-Boltzmann law, and my math based on those articles, are correct (I've found that technical articles like these tend to be pretty accurate), an unprotected human in space will have a net heat loss of around 750 to 1000 watts depending on their size (and thus surface area). If we go to the Human power article, we see that humans are performing very well if they can manage half a horsepower (375 watts) while some top athletes can manage around 500 watts. So even under ideal conditions, an unprotected human in deep space has a 250-500 watt net heat loss. If we assume that our hypothetical human has a mass of 70 kg and the specific heat capacity of water (4.1813 J/(g·K) - though I think the actual value for human tissue is somewhat lower than this, meaning it takes less energy loss per degree), we determine that our hypothetical human's body temperature will drop 1 degree Celsius for every 293 kJ of energy lost. A 250 watt net energy loss represents a loss of 0.250 kJ per second, or 15 kJ per minute. Under these circumstances, the person would drop 1 degree Celsius every 20 minutes, and would be suffering from stage 2 hypothermia in about an hour. Now keep in mind, this scenario represents a human at full output. The baseline power output for the average person is around 100 watts, which would mean a net deficit of of 650 to 900 watts (an energy loss of 0.650 kJ per second or 39 kJ per minute using the smaller figure). This person's temperature would drop 1 degree Celsius every 7.5 minutes, and would be entering stage 3 hypothermia in about half an hour (if we use the maximum calculated heat loss rate, 900 watts, or 0.9 kJ per second, the poor sap would lose 54 kJ per minute, and drop 1 degree Celsius every 5.5 minutes, arriving at stage 3 hypothermia in about 22 minutes).

This is just a quick and dirty approximation. We'd need to go into more detail with stuff like the thermal conductivity of the the tissue between the body core and the surface of the skin to develop a truly accurate theoretical model.

[Chrome]

most of the ship's operational heat would be dissipated by dumping it into the outgoing exhaust particles

Unless we're going with unreal physics, to do that whatever it is you're using to dump the heat must be hotter than the exhaust gas, otherwise the exhaust gas would heat it up, no the other way round.

Assuming the Wikipedia articles on Black bodies and the Stefan-Boltzmann law, and my math based on those articles, are correct

I got very similar effects running the same numbers, however I think you're overlooking the application of Planck's Laws (IRRC) where the rate of energy loss is proportional to the difference in temperature between the environment and the object. Your figures work out just dandy but only account for the amount of heat radiated naturally by the human body, not the amount that is lost due to external cooling. So, on your figures you'd be talking about how this would progress if the environment you're in is the same temperature as the body at all times: the equations so far only indicate how quickly the body would freeze based on it's radiated loss that is produced at room temperature - when exposed to absolute zero the rate is proportionally higher.

The final figures I arrived at shows a human body of roughly average statistics dropping to 10k in roughly eight hours five minutes, give or take, but reaching the .3k could take years.

This is just a quick and dirty approximation. We'd need to go into more detail with stuff like the thermal conductivity of the the tissue between the body core and the surface of the skin to develop a truly accurate theoretical model.

In every study i've seen which goes into conductivity and human tissue you can make an analogue to plain water - the difference is negligible.

[Joz]

What if the vents are just that vents, and by using a stored gas under pressure, with a high conductivty rating, and releasing that gas whene needed to cool heatsinks under the vents.

though...it may throw some (most ) forms of stealth out the window...

Expelling the compressed gas pass heatsinks (and out the vents) would account for why ships have vents. And becouse of the advancement of SW tech (compared to our own,) its resonable to assume that the heat needed to be disspated by onboard mechanical and electronic devices is low enough that a ship can let the heat build up in the heatsink, and then every (measure of time,) use a controled burst of the pressurized gas to rapidly cool down the heatink (and thefore the electronic/mech, the HS is conected too.)



Just my crapy 2cents.