Does water get freezed under vacuum?

Water vaporizes in a vacuum. The greater the vacuum pressure or water temperature, the faster it vaporizes. Ice will sublimate in a vacuum.

add: the faster it vaporizes, the lower the temperature. Yes, water will freeze in a vacuum, and oddly, it will be boiling when it does.

Its true.In Yarn conditioning machines steam is generated in Vacuum conditions and is produce at55Deg Instead of the usual100Deg.C

You are correct, Guest.

DVader, ice can certainly sublimate if under vacuum, but will remain solid ice under a certain temperature, which I can't remember off the top of my head --> Comets are stable chunks made largely of ice and begin to sublimate and make a tail of gas as they are heated by solar radiation when close enough to the sun.

To the poster, if you are putting a little bit of water in a vacuum chamber, chances are it will all boil off long before it solidifies. If you want ice in a chamber, you'll need to cool it and/or start with enough water/ice that it can cool itself down through evaporation enough to solidify at whatever pressure you are pulling down to, and not be able to pull significant energy from its container (very well insulated, and very cold container). If you are using a cryo pump to pull a hard vacuum, you'll probably want to start with VERY cold (cryo cold) ice rather than water. If you don't, the water vapor form evaporation/sublimation will be fairly considerable and will coat the cryo pump surface enough that it won't be effective (easy to fix, just heat it back up while under vacuum while running the roughing pump, but your test will be shot).

Comet tails may not be the water as the ice in them is a mixture of helium, hydrogen, nitrogen and ammonia with sometimes water.

It's the old thing that's printed on any food that contains water, needs to be cooked, and might be used in camping... They cut the time down for cooking if over 5000 feet altitude because the lower atmospheric pressure makes things boil at lower temperatures.

"They cut the time down for cooking if over 5000 feet altitude..."

I believe that cooking time INCREASES with higher altitudes, because the lower temperature at boiling point means that less thermal energy is being provided per unit of time. Pressure cookers, which effectively lower the altitude by increasing the pressure inside, cook foods faster than (normal / standard) atmospheric pressure.

You got it, again, Ron.

The fact is you better go read the cook book again, water does boil at a lower temperature, but you need increased time to compensate for the lower temperature.

Yes, this is necessary because the time to deactivate (kill) bacteria is temperature sensitive. For example, if you want to destroy most bacteria in water, it is desireable to boil for 5 minutes at sea level (ie: 212F). I am lead to understand this can also be accomplished by maintaining the water at 160 F for 8 hours. If you increase your altitude, the temperature at which the water boils is reduced, so the time to kill bacteria is increased.

I believe it is the pressure that enables water to boil at lower temperature and not the time.

PV/T=C (constant); assuming V (volume) being constant, the only variables are P, pressure & T, temperature. Increase P then T must go down to satisfy the equation.

"PV/T=C (constant); assuming V (volume) being constant, the only variables are P, pressure & T, temperature. Increase P then T must go down to satisfy the equation."

Try it with numbers to see why this is incorrect. Let V = 1 to simplify (and meet your constant volume assumption). Suppose that P = 6 and T = 2; then C = 3. If P is increased to, say, 9, then T must INCREASE to 3 to satisfy the equation.

Or rearrange terms: let PV = TC (that is, we've multiplied both sides by "T"). With V and C both constants, if P increases, so does T, and vice-versa. Q.E.D.

So this is why when I don't use my ice cubes very often, they simple disappear from the ice trays?

Vermin,

Yes. Since the refrigerant coil is colder than the ice, the partial pressure of water in the air at the coil is lower than that at the surface of the ice. So over time, you see these cubes shrinking (and rounding a little as they shrink in size). This is also the cause of "freezer burn", which happens in a sealed container with air present inside. When our children were young, we had no clothes drier, so all went onto the line outside. In winter, they would freeze then dry, so I joked that our clothes were "freeze-dried".

--JMM

Partially so - if you have a frost-free freezer, it has a heater that kicks in periodically and raises the temperature to where the hoar frost on the freezer walls will melt and be drawn out as condensate. Some of the ice cube surface will also melt and over weeks, they...will....go.....away......

^{But where do they go away to??? And who is seducing the ice right out from under my freezer???}

Somewhat higher West of the Mississippi.

Ah, Vermin! Because the water boils at a lower temperature with decreased atmoispheric pressure, as up on mountains or increased elevation, that means that the water temp never reaches 212 F (100 C), which means that cooking times are longer. Ever try boiling potatoes at 3,000 meters altitude?

No. I was too busy flapping my arms and trying not to die.

If you can get your hands on a book called "Modern Airconditioning and Refrigeration" it covers this topic well. Briefly it is a real problem when trying to dry systems out as the water can easily freeze under vac, either lots of time or applying heat can help. The other method used is vac then flush with dry nitrogen, vac, flush until satisfied.

I once put a beaker of water into a vacuum chamber with no boiling. I finally realized (after I started the vacuum pump and it still didn't boil) that the high heat of vaporization of water causes it to evaporate quickly, but not boil as we expect. It does not bubble up from the entire volume, but quietly disappears.

A heat source would change this quickly.

You are Right.But if some heat is applied steam is generated at lower temp.Good commentsand interesting discussion.

Isn't there a graph in "Perry's" (Mollier Diagram?) that charts vapor pressure as a function of temperature and pressure. The rate of sublimation or evaporation is a function of the vapor pressure of the substance (water, which changes with temp and/or pressure ) and the difference in the environment pressure.

Under vacuum conditions a cup of room temperature water will boil until it freezes. Around 1/2 to 2/3 boils away before it reaches this point. Not only, but a styrofoam cup filled with liquid nitrogen does exactly the same thing. I've made nitrogen ice this way using a home-brew vacuum chamber.