Does 0g have an effect on water?

[dstebbins]

In open space, water basically turns to snow. It turns to a gas due to the reduced air pressure, and then freezes due to the low tempurature, resulting in common snow. In fact, this is how snow is created on earth; the water expands due to the lowered air pressure high in the sky, but also freezes due to the cold winter temperature.

 

But what about in a spaceship? The metal walls will keep the air pressure intact, and it can also be artificially heated to prevent... well... the astronauts from freezing to death.

 

Would having no GRAVITY actually have any immediately noticeable effect on the water? If so, how do astronauts solve this problem?

Edited June 7, 2012 by dstebbins

[CaptainPanic]

I'm not convinced you have actually understood how this all works...

 

All your answers can be found in the Phase Diagram of water.

 

The two parameters of importance are the vapor pressure, or partial pressure of water, and the temperature. When you know those two, you can look up in that phase diagram what the water will be like: vapor, liquid, solid or supercritical.

 

Also, it will show you what kind of ice will form... at interstellar temperatures (just a few Kelvins), and very low temperatures, you actually get a different type of ice than here in our atmosphere (see that same phase diagram for more info).

 

And finally, gravity has no influence on this phase diagram. Gravity only holds our planet together, and holds our atmosphere here. But astronauts in a space ship only need to concern themselves with the phase diagram of water, not gravity (at least, when it comes to the state of water).

[D H]

In open space, water basically turns to snow. It turns to a gas due to the reduced air pressure, and then freezes due to the low tempurature, resulting in common snow. In fact, this is how snow is created on earth; the water expands due to the lowered air pressure high in the sky, but also freezes due to the cold winter temperature.

This is not quite right. Liquid water cannot exist in equilibrium at pressures below the triple pressure, ~612 Pa. That's about seven orders of magnitude higher than the pressure in interplanetary space (~10^-4 Pa, or less). Talking about what happens to liquid water in vacuum is asking about non-equilibrium physics. For example, what would happen if a glass container holding liquid water was sent to outer space and then shattered?

 

The water would boil -- at least at the boundary. The boiling would be very explosive. The vapor would not form into snow. However, the explosive nature of the boiling would create droplets that would in turn explosively boil into micro-droplets, and some of these micro-droplets might turn into snow. The reason is that the act of boiling steals heat from the remaining water due to heat of evaporation. Heat of evaporation would also make some remnant of the original quantity of water freeze. End result: A lot of individual water molecules, many small particles of ice (which sublimate rather quickly), and several larger blocks ice (which will sublimate over astronomical timeframes).

 

 

But what about in a spaceship? The metal walls will keep the air pressure intact, and it can also be artificially heated to prevent... well... the astronauts from freezing to death.

 

Would having no GRAVITY actually have any immediately noticeable effect on the water? If so, how do astronauts solve this problem?

Too me this is a much more interesting question. Astronaut Don Pettit (also a PhD chemical engineer) has done a number of "Saturday Morning Science" experiments with liquids in space. You can see several of them at this site: http://physicscentral.com/explore/sots/. One of them, "Episode 2: Bistro-nauts", obliquely discusses fuel tanks. How do fuel tanks work in zero G? This is a big problem! There are basically two solutions. One is to put a bladder in the tank. The fuel is on one side of the bladder, a pressurized gas on the other. As fuel is removed, the gas expands and forces the bladder to keep the fuel intact. The other is bladder-less tanks, which use surfaces with weird, sharply angled shapes to move the fluid toward the port thanks to surface tension. Google the term "propellant management device" for more info.

Edited June 7, 2012 by D H