Watching Dr. Who.
The Doctor just said that, in space, your saliva and sweat would boil, indicating that with zero pressure water turns to a vapor.
I'm not sure that's correct.
wiki's got a fairly good article on phase diagrams:
https://en.wikipedia.org/wiki/Phase_diagram
This goes down to 1 Pascal, at which point the boiling point i about negative sixty C.
That's low, but it's not 0 K low. But, 1 pascal is also not 0 pascal, so I'm not entirely sure.
Insights?
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youtube.com - Space Suit Testing
ReplyDeletethis person described saliva boiling off of his tongue when he was exposed to pure vacuum
I’d believe it — I know vacuum boiling is a thing from NASA’s big vacuum testing chamber.
ReplyDeleteAlso, the boiling point of a fluid is when the partial pressure of its vapor dissolved in it is equal to the partial pressure of its vapor outside it. If you actually manage zero Pascal, the partial pressure would by definition be zero and the only question is how quickly it evaporates/sublimates, not whether it does.
Uh... how would your saliva get down to anywhere near 0K in a vacuum? I thought vacuum was pretty notoriously bad at changing the temperature of things.
ReplyDeleteYou’ll lose some temperature to expansion, but only if it’s gas and can expand. Otherwise... black-body radiation? I don’t have a great idea how fast water throws off heat that way.
Feeling the limits of my basic physics and chemistry here.
Nice. Things get funny as you get close to 0 pressure.
ReplyDeleteSimilarly, we were watching some SF show. They lost pressure in a room filled with water, which froze instantly.
ReplyDeleteNo. The heat cannot leave water that fast.
According to everything I've read just now, what happens is first the water boils into vapor and then the vapor freezes. This apparently has been frequently observed by astronauts and it makes sense to me.
ReplyDeletethis article seems to cover all the details and has phase diagrams that go below 1 pascal.
https://medium.com/starts-with-a-bang/does-water-freeze-or-boil-in-space-7889856d7f36
Of note, "boiling" doesn't mean it's hot.
ReplyDeleteyoutube.com - Egg in a Vacuum Chamber
Veles Svitlychny: See, that makes sense to me. I understand where the energy is going there (from a compressed mass of water to an expanding-and-cooling cloud of gas, to an expanding-and-cold cloud of crystals).
ReplyDeleteDr who is not the place to look for science in your science fiction?
ReplyDeletePatty Kirsch Yes, but: It does try to be educational. For the British children.
ReplyDelete