Thought experiment

[bjxrn]

I have a question about how liquid water behaves in space. You cant have liquid water in space is probably your retort but here is the question that i thought about after a strange dream. Sorry to interupt the more serious astronomy questions on this board.

Lets say that a body of water with a diameter of 100m and a temperature of 37 degrees celcius somehow leaks out of a huge space station. this ball is perfectly spherical and in the center of the body a diver with scuba gear is located.

First, how long will it take for the temperature of the water to reach 7 degrees celcuis?

How will the ball of water behave? since there is no atmospheric pressure in space, how will the surface of the body react to that?, will it turn to gas or freeze?

How long will the scubadiver survive in the center of this body of water? Give me a guestimate, what will kill him?, my guess is suffucation or if he has enough oxygen hypothermia from the water getting to cold.

EDIT: Ok, the diver will obviously die from the lack of atmospheric pressure and not from suffucation or cold, silly me.

[antoniseb]

You'll want to give us a few more specifics. How close to the Sun is this sphere of water? (Is it out in intergalactic space? that would give different numbers.

Though I think you can be pretty sure that the SCUBA diver will run out of air long before the center of a 100 meter sphere of water freezes.

[Krowser]

So THATS how comets are made!

The only thing left to do now is grab a handful of oil rig workers and ship them off to the closest comet we can find to see if there actually is a scuba diver inside.

You know what, that could work in some sort of old cultural legend. The spirit of the scuba diver is controlling the comet and they are perpetually trying to get warmer, and thats why they are orbitting the sun.

Sorry about that, mornings are intense for me.

[bjxrn]

It is in low earth orbit next to the ISS. The diver will be dead because of the lack of pressure. Anyone have any idea how the ball of water will act?

[Krowser]

Well, if as you said the water leaked out of a space station, it will be dispersed left and right and the diver will quickly realise he's wearing the wrong suit. Because of the temperature I'm pretty sure the station would be shooting ice instead of water.
Actually, make that snow since it would be pulled by vacuum. It's pretty much the same way a snowmaker works on ski hill.

But lets say it was "teleported" outside in one instant, it would start tearing appart because of the gravity of the local stellar bodies.

On the other hand, if it was in dead space, if should keep the spherical shape and start freezing.

[Scamp]

EDIT: Ok, the diver will obviously die from the lack of atmospheric pressure and not from suffucation or cold, silly me.

No, silly me. I still don't get it. Why wouldn't the water provide a suitable environment for the diver until it freezes or he runs out of air?

[bjxrn]

Lets assume that a ball of water with the diameter of 100m is teleportet into low earth orbit, appearing perfectly spherical.

[bjxrn]

No, silly me. I still don't get it. Why wouldn't the water provide a suitable environment for the diver until it freezes or he runs out of air?

Because the amount of water above the diver is not enough to compress the water to a level of pressure that is suitable for humans. On earth if a diver is 50 meter below the surface of the water the gravity of the planet makes the pressure of that body of water rise. But because that is lacking in space you dont get a suitable environment in the ballbody of water, even though the temperature is quite nice.

[chornedsnorkack]

Letīs make a few quick calculations.

At 37 degrees, the vapour pressure of water is over 60 mbar.

At 60 mbar, water expands roughly 20 000 times on boiling. But since there is complete vacuum outside, the vapour will be escaping to infinity at roughly the speed of sound. Say 500 m/s, which would mean that in a second, 2,5 cm of water would evaporate away.

Except that this takes heat. The heat of water boiling is about 550 calories per gram, cooling water to freezing is about 37 calories (not exactly) so that evaporating a unit of water takes cooling down 15 times the volume of water - roughly 40 cm in a second. Which cannot happen - water is not that good a conductor of heat, and there is no convection without gravity. What happens is that in a fraction of second a thin layer on surface cools down, and the evaporation slows down a bit. For example, when the surface reaches freezing point, the vapour is still escaping at the speed of sound, but the vapour pressure has decreased ten times. Also, the remaining water starts to freeze. The latent heat of freezing is about 80 calories, so applying vacuum to 0 degree water evaporates roughly 1/8 of it, and freezes 7/8. Of course, the ice cools further - in interstellar space, it will get pretty cold.

On Earthīs orbit? Well, the solar constant is about 1,4 kW per square metre. So about 330 calories, enough to evaporate roughly 0,6 g or so water. If it is escaping at 500 m/s, its pressure turns out to be 0,3 Pa. 2000 times lower than the vapour pressure at 0 degrees. So, roughly what is the temperature of ice in sunlight?

But before the water mass slowly conducts the heat from inside out, the bubble of scuba diverīs exhaled air starts to expand, and water also evaporates from the inside of the bubble. Yet it is a small bubble, a few l, and it has to accelerate half a million tons of water.

But what will water do at 37 degrees and no pressure? Will it behave as an overheated fluid and evaporate only from surface (so that the rest freezes into a solid piece), or will it nucleate bubbles all through the volume and expand into snow?

[bjxrn]

thank you so much, anyone else?

[grant hutchison]

But what will water do at 37 degrees and no pressure? Will it behave as an overheated fluid and evaporate only from surface (so that the rest freezes into a solid piece), or will it nucleate bubbles all through the volume and expand into snow?

The ambient pressure will drop to zero throughout its volume pretty quickly. So it should start to nucleate bubbles everywhere, each one expanding with a pressure of 60mb.
Somewhere on You-Tube there's a video of a water spherule in freefall, with an effervescent tablet of some kind stuck in it: the thing managed to hold together under surface tension while bulking up into a mass of gas and liquid. I'm guessing something similar might happen to our water sphere as it simultaneously evaporates and cools throughout its volume, so that the diver ends up embedded in a loose mass of ice crystals formed from the bulk of the water.

Grant Hutchison

[mugaliens]

Ok - let's start with the givens:

Given: [quote=bjxrn;1436410]Lets say that a body of water with a diameter of 100m and a temperature of 37 degrees celcius somehow leaks out of a huge space station. this ball is perfectly spherical and in the center of the body a diver with scuba gear is located.

Find:

First, how long will it take for the temperature of the water to reach 7 degrees celcuis? How will the ball of water behave? since there is no atmospheric pressure in space, how will the surface of the body react to that?, will it turn to gas or freeze?

Thermodynamics was one of my least favorite subjects. Heat and mass transfer I did well in, but was still a big flush.

My guess is that if the scuba diver holds real still, so as not to cause major portions of the water ball to be flung off into space at faster than the tiny escape velocity such a relatively massless football field-sized swamp might have (whatever you do, don't sneeze...), then the ball of water will simply begin boiling away due to the near-zero pressure, most notably on its surface, but not much different (1/1000th of a psi?) at it's center.

As the water evaporates, it will extract heat from the remainder (the latent heat of evaportation), making it colder. It will get to 7 deg C before all of it has evaporated.

How long will the scubadiver survive in the center of this body of water?

About a minute.

Give me a guestimate, what will kill him?,

A very severe case of the bends. But he will loose consciousness in about 11 seconds due to the lack of partial pressure of oxygen in his lungs. Contrary to misbelief, he won't boil (at least not much). Rather, in a couple of minutes, his brain will stop functioning, followed (possibly preceded) by the stopping of his heart.

...my guess is suffucation or if he has enough oxygen hypothermia from the water getting to cold.

He won't live long enough.

EDIT: Ok, the diver will obviously die from the lack of atmospheric pressure and not from suffucation or cold, silly me.

Now you got it! The on the right track part, not the silly part - common mistake.

Now - if the ball is 1,000 meters, it's a bit of a different story...

[bjxrn]

My internal dream physics rendering engine that animates my dreams is totally of. I dreamt of swiming around in a beautiful blue ball of water looking down at the earth. My updated physics engine will render a dead diver frozen solid in a huge cloud of water gas. Science, crushing dreams since 1700

[grant hutchison]

By the way, did you know that a diver in a blob of water in space features briefly in David Brin's novel Earth?

Grant Hutchison

[eburacum45]

Try putting the water inside a stout, transparent plastic bag. The bag only has to withstand one bar of pressure. For as long as the bag stays in one piece, you'll be swimming around like a goldfish at a fair.

Until the bag bursts, probably because its been punctured by one of those pieces of mashed up satellite that are zooming around up there. Then it'll start boiling out into space through the puncture. Make a nice rocket...

[alainprice]

Isn't the scuba divers air supplied from pressurized tanks? What is it....over 1500 psi? Add a regulator and you're in business. We're obviously talking spring operated due to such low pressure outside.

Also, remember that water appears to boil from the inside out when weight is missing.

[bjxrn]

So what, a plastic bag surounding the sphere that can withstand 1 bar helps to solve the pressure problem and I wont die horribly? How does that work?

[eburacum45]

Obviously, if the bag can withstand the pressure the water won't escape and boil away, so no cooling, and no freezing.

In practice the bag would expand somewhat, and the pressure would drop, probably accompanied by the formation of a few vapour bubbles. But the bag would quickly reach equilibrium, and you could have a quick swim. I wouldn't wait too long, though- the bag is under pressure, and any puncture will release that pressure in a jet.

[chornedsnorkack]

People routinely live in spaceships and space stations. Part of spaceship outer wall is nontransparent, but they do have windows.

What are spaceship windows made of?

Certainly, a spaceship could be hit by a piece of space debris. When it happens, air runs out of the ship, and the people inside suffocate. I do not think a manned spaceship has met space debris yet, but some spaceships have decompressed with fatal results.

What happens if a spaceship window suffers a small leak, where air escapes at an appreciable speed, but there is a lot of air still in?

How would you design a really big panorama window to limit the spread of cracks without spoiling the view? Like, the Schmidt corrector plate - what happens if a meteorite hits it?

Suppose you had a spaceship with a single, spherical, 30 000 square m window, and 500 000 tons of water inside. If it did spring a leak, water has a much larger density than air, and therefore it does not achieve the same speed when powered by the same pressure. If a leak of given geometry lost 1 cubic m of air per second, my guesstimate is that the same leak would leak only 30 l of water or so per second. So, a spaceship which is a leaky swimming pool panorama window is not all that desperately unsafe.

But how do you stop crack/tear propagation in a loaded structure where no optical inhomogeneities are allowed?

[grant hutchison]

Isn't the scuba divers air supplied from pressurized tanks? What is it....over 1500 psi? Add a regulator and you're in business. We're obviously talking spring operated due to such low pressure outside.

It depends a little on how the regulator works, but the depressurized diver will inevitably run into pressure problems at some point in the respiratory cycle.
You need maybe 100mmHg of oxygen, absolute pressure, in your lungs to move oxygen into adequate solution in the pulmonary capillaries. But our depressurized diver has effectively zero pressure outside his chest and in his various tissues. Not only will the oxygen pressure in his lungs prevent him breathing out, it will be enough to close off his lung circulation and the venous return to his heart. So if he gets enough oxygen pressure from his regulator to push oxygen into his circulation, his circulation fails.
More likely, the regulator needs a slight sub-ambient pressure to trigger (how do you get below zero ambient pressure to trigger it?) and delivers flow at a slight over-ambient pressure once triggered (not nearly enough oxygen partial pressure to sustain life, if ambient is zero).

Grant Hutchison

[eburacum45]

I do not think a manned spaceship has met space debris yet,

This one did;
http://www.aero.org/capabilities/cor...ris-risks.html

This 4-mm-diameter crater on the windshield of the space shuttle orbiter (see image above) was made by a small bit of space debris determined to be a fleck of white paint approximately 0.2 mm in diameter. It was traveling at a relative velocity of 3-6 km/sec when it impacted.

Other impacts have occured. They are rare, but not unknown.

[mugaliens]

Until the bag bursts, probably because its been punctured by one of those pieces of mashed up satellite that are zooming around up there. Then it'll start boiling out into space through the puncture. Make a nice rocket...

Congrats, eburacum45 - you just earning my "I made Mugs' evening!" award!