Basic pressure question

[Airmid]

Here's a very basic pressure question:

Suppose I fill a balloon with very pure water, and place it in a vacuum chamber. What will happen? (Assume there's absolutely no gas present in the balloon.)

 

I can think of several scenarios:

- nothing happens, because liquids don't expand

- some of the water will vaporize, because it's being subjected to vacuum, and will expand the balloon

- very little water will vaporize, because the elasticity of the balloon creates pressure, so nothing happens

 

Can you help me out?

Airmid.

[insane_alien]

Some water will vapourize until the balloon supplies enough pressure to prevent any more water vapourizng. if the balloon fails(bursts) before then all the water will vapourize assuming the chamber is big enough.

[swansont]

Liquids do expand, but water is almost incompressible — the expansion (or compression) coefficient for water (inverse of the Bulk modulus) is very small. Then, as i_a notes, you have to rely on the balloon supplying the pressure that the atmosphere was previously exerting.

[Airmid]

Thanks!

[BramVandenbo]

There are 3 things to know:

1) The air pressure is about 100.000 Pa underpressure.

(The pressure of the water inside the balloon is not worth mentioning because it is so small compared to the pressure outside the balloon.)

 

2) The elasticitymodulus of latex is about 10.000.000 Pa if I am not mistaken(?) (This should of course be pretty small compared to other materials.)

 

3) Latex can stand about 15 000 000 Pa. (according to wikipedia)

 

Some calculations and conclusions:

 

1) E = 10.000.000 Pa = stress/strain = 100.000 Pa/(extention/originalsize)

extention/originalsize = 100.000/10.000.000 = 0.01

As you can see the balloon only gets 10% bigger.

 

2) The latex can stand a lot more pressure so it will not explode.

 

Ok, so the most important thing is that the balloon gets 10% bigger. (Actually it will not even be that much as the pressure inside the balloon will get lower as the balloon expands, but not much). Now we can calculate what the influence will be on the water!

 

Actually (at 25C°) water starts boiling at 0.01 of normal pressure. ( I found a nice drawing of the curve at the following website.

http://van.hep.uiuc.edu/van/qa/section/States_of_Matter_and_Energy/Boiling_Evaporating_and_Condensing/976072539.htm )

 

Conclusion is: the water will not boil.

 

Please correct my mistakes I'm only a student industrial ingenieer. Not a prof

[insane_alien]

water doesn't expand very well. it also does not behave like a gas as it is a liquid. assuming no gas is in the balloon(either dissolved in the water or separated from it) if the balloon were to expand in any way this would cause a vacuum thus the water would boil. since this releases water at a pressure of 3167.197432 Pa. also the pressure inside the balloon before removal of the external atmosphere is atmospheric pressure + the pressure exerted by the latex balloon.