Airlock full of water exposed to vacuum

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Eebster the Great
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Airlock full of water exposed to vacuum

Postby Eebster the Great » Wed Feb 21, 2018 7:45 pm UTC

In a popular* movie, a woman is trapped in an airlock filling with water whose inner door is inexplicably jammed. Eventually, the pressure of the water causes the outer door to burst open. The water boils then freezes almost instantly, leaving the woman's frozen body and a bunch of ice.

Is this realistic? How long would it take 50 m3 of water at room temperature and pressure (at the surface) to boil and freeze when suddenly exposed to a vacuum?

*In a certain sense

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Re: Airlock full of water exposed to vacuum

Postby Tub » Wed Feb 21, 2018 10:39 pm UTC

Haven't seen the movie (not that popular, apparently), but here's the phase diagram of water:
https://upload.wikimedia.org/wikipedia/ ... _water.svg

There are plenty of youtube videos of water in a vacuum chamber, and in many of them the water will boil violently for a while, then sit around, then freeze a few minutes later.

Question is, do you get solid blocks of ice, or do you just get a bunch of disconnected cold water molecules? In an endless vacuum, anything that boiled off will be gone, and won't come back to form solid blocks.

Those vacuum chambers have maybe ~100 Pa (anything less is way expensive), and at that pressure water will freeze around -10°C. Outer space has at least 5 order of magnitude less pressure, putting the freezing point below -60°C.

Now outer space is colder, but a vacuum is a pretty good thermal insulator, so its temperature is largely irrelevant. The dominant causes of temperature loss should be boiling and gas expansion.

Is it possible for a blob of water to cool its core to -60° before everything's boiled off? Depends on size and surface area, I suppose. If you opened an unpressurized airlock, that'd be a good start. An exploding airlock with water shooting out in all directions will probably cause more surface area than you'd like.

Then again, I haven't done the experiment, and I don't plan to.

(Btw, what's the cause of death in the movie? Freezing or being crushed by water pressure?)

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Re: Airlock full of water exposed to vacuum

Postby speising » Wed Feb 21, 2018 10:50 pm UTC

the water will only freeze fast in the vacuum if it is sprayed into a fine mist.
the woman will have enough mass / little surface to take quite a while to freeze, so "leaving the womans frozen body" is not realistic. rather, it will probably dessicate before it freezes. anyway, the proximate cause of death is lack of oxygen, either by drowning or suffocating.

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Re: Airlock full of water exposed to vacuum

Postby Xanthir » Wed Feb 21, 2018 10:52 pm UTC

Per this Medium post from a science-y person that seems credible, no, it's definitely not realistic. Water will boil immediately when exposed to the vacuum, and violently so, but it takes a bit to freeze (due to water's huge heat capacity). However, when it boils it goes immediately to vapor, which maximizes the surface area/volume ratio, and promotes quick freezing. So you get an explosive boil resulting in a rapidly expanding cloud of fine frozen vapor, aka snow.
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Re: Airlock full of water exposed to vacuum

Postby jewish_scientist » Thu Feb 22, 2018 1:41 pm UTC

I actually remember looking into this back in high school. My question was more along the lines of 'if space is so cold water should freeze and the pressure is so low that it should boil, which happens?' Basically, the water boils faster than it freezes, so it becomes a gas. However, if you look at a phase diagram of water, the bottom left is labeled solid. When water vapor sublimes into a solid (without growing off of anything nearby) results in something most of use are quite familiar with; snow.
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Re: Airlock full of water exposed to vacuum

Postby Himself » Fri Feb 23, 2018 4:00 am UTC

If this happens around Earth's orbit the solar radiation might be enough to keep the water from freezing, considering what happens to comets.
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Re: Airlock full of water exposed to vacuum

Postby Xanthir » Fri Feb 23, 2018 8:52 pm UTC

The vacuum temperature in Earth orbit is still super-freezing. We're just close-enough in that at equilibrium water will absorb enough solar radiation to stay liquid. (I think it also still has to be in a large enough body, but I don't know what that limit would be.) So it'll definitely still freeze at first, at least.
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Re: Airlock full of water exposed to vacuum

Postby Eebster the Great » Wed Feb 28, 2018 2:54 am UTC

jewish_scientist wrote:When water vapor sublimes into a solid (without growing off of anything nearby) results in something most of use are quite familiar with; snow.

Sublimation is the reverse process: a solid turning into a gas. You are referring to deposition/desublimation, and that isn't exactly the source of snow, but it is the source of frost.

I understand that water boils very quickly when exposed to a vacuum. That's what happened. I also understand that as it boils, its temperature will drop very quickly. Eventually, the remaining liquid should start to freeze as it boils. And at some point you will expect to have no liquid left, just solid and gas, since the temperature and pressure are far below water's triple point. (And since the remaining solid will have some residual thermal energy, it will also eventually sublimate, but that takes a much longer time.)

What I don't know is how long the process would take. Could you really boil off tons of water in less than a second? And if you could, would any solid be left? I agree that either way, the frozen corpse is a bit implausible, since the skin will never boil and there is no way to expose the water in the body to boil it or rapidly cool it, but it isn't obvious in the movie that her body was actually frozen, just that there were a bunch of ice crystals on the surface. Either way, I'm more interested in the water than anything.

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Re: Airlock full of water exposed to vacuum

Postby jewish_scientist » Wed Feb 28, 2018 1:10 pm UTC

I though sublimation refereed to that process in either direction. Learn something new everyday.

My science teacher told me the same thing about space snow. Still, I think it is a lot more poetic and technically not false to say that it is snow, so that's what I will say.
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Re: Airlock full of water exposed to vacuum

Postby trpmb6 » Tue Jun 19, 2018 6:15 pm UTC

I didn't intend to reanimate this thread.. But I was discussing this topic with someone else when the movie the OP mentioned was brought up. Apparently in that movie they were in a parallel universe and the scene in question was being used as a tool to show that the laws of physics (as we understand it) were different in this parallel universe.

Apparently this is also demonstrated later on in the movie when there is another scene (though quite subtle) that shows water being boiled off into a vapor cloud.
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Re: Airlock full of water exposed to vacuum

Postby Eebster the Great » Tue Jun 19, 2018 6:33 pm UTC

It seems unlikely that not only would humans evolve in a parallel universe with significantly different laws of physics, but that the exact same people would live in a virtually identical society except for a few very subtle differences regarding employment decisions and the like. Though maybe that was yet another universe. The whole thing didn't make a lot of sense.


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