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Forever boiling water in vacuum

  1. Jun 19, 2015 #1
    Hello
    my first post :)

    I was wondering if it could be possible to achieve forever boiling of water in room temperature in vacuum.
    I understand that as water evaporates pressure increase and when equilibrium is reached, water stops boiling.
    But could it be possible to do that vapor in vacuum reaches its maximum content and condense back to liquid and maintains pressure?
     
  2. jcsd
  3. Jun 19, 2015 #2

    CWatters

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    Not in a vacuum.

    If there is water vapour it's not a vacuum anyway.

    If you inject water into a sealed vessel containing a vacuum the water will boil forming water vapour. If you add sufficient water and maintain everything at room temperature then the pressure will rise until it reaches around 2.5 kPa when boiling will stop...

    https://en.wikipedia.org/wiki/Vapour_pressure_of_water

    You won't see bubbles of water vapour forming (the normal definition of boiling) but molecules of water will move back and forth between the water and water vapour.
     
  4. Jun 19, 2015 #3

    Baluncore

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    vec738, welcome to PF.
    But what if I have a closed glass container with a cool top and a slightly warmer base. I start with water covering the base and pull a partial vacuum. Bubbles of steam will then form on nucleation sites near the top of the warm liquid, (where the hydrostatic pressure is least), the steam released from the bubbles will rise to the cool top surface where it will condense and drip back down to the pool below. That should be a continuous process so long as I supply sufficient energy to maintain the temperature difference.
     
  5. Jun 21, 2015 #4
    If the water is boiling, there is water vapor, and therefore no vacuum. So strictly speaking, it is not possible to boil water in a vacuum in the first place. If you are talking about "below atmospheric pressure", then let me use this analogy:

    If you take a sealed container with only water and air, boil the water at the bottom and cool the top. then the water will start boilng, the pressure will increase a bit, the steam formed will condense, and the cycle continues. If you stop cooling the top, pressure will buildup as long as you keep heating it and that the container doesn't blow up. Pressure will only depend on the temperature of the water.

    If you take the same scenario, but replace air with vacuum, the very sime thing happen, except that there is no air and that you can make it work at lower temperature and lower pressure.
     
  6. Jun 21, 2015 #5

    Baluncore

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    A room temperature experiment. Take a 10ml syringe and first draw 1ml of water, then seal the syringe and draw slowly against atmospheric pressure to 10ml, you will see the water boiling to produce clear steam at room temperature. When you allow the plunger of the syringe to return, it is drawn back to the 1ml mark as the steam condenses back to liquid water. The syringe then contains only the original 1ml of water.
     
  7. Oct 30, 2015 #6
    This is a very interesting problem to me. Consider a small sphere partially filled with water in equilibrium with its vapor pressure exactly at the temperature consistent with boiling point of the water under those conditions. Assume the whole sphere is in a sealed blackbody cavity at that temperature. Then consider the time evolution of this system. As it boils, the liquid cools below the boiling point and the vapor temperature is above it. The boiling stops for two reasons, the water is below the boiling point and the vapor pressure is higher which raises the boiling point above even the starting temperature of the water. Then as the vapor cools to ambient its pressure goes down and the liquid rises to ambient. Eventually, will not equilibrium be restored and will it start boiling again?
     
  8. Oct 30, 2015 #7
    When I was in high school one of the students brought water to its triple point. So she had boiling water with ice floating in it.

    It wasn't a closed system, though.
     
  9. Nov 3, 2015 #8

    cjl

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    Yes, and this is actually a very, very good way of transferring heat from the hot side to the cool side, since the amount of energy to boil a liquid is quite large. This is how heatpipes and vapor chambers work, both of which are commonly used in electronic devices to transfer heat from high power integrated circuits (like CPUs and graphics cores) to heatsinks where the heat can be dissipated by a fan.
     
  10. Nov 7, 2015 #9
    I was thinking of this vacuum box in space you's are talking about, and how the water boils, and how the heat distributes the atoms evenly, and even if the water drips back down by gravity, all the water is at bottom yes but all the heat is distributed into the metal container and the water, and to add more heat it'd have to be attached to atoms say earth, but then it doesn't get any hotter at the water atoms since all heat equilates distributed evenly now soon~..........oh wait the water being in vacuum should boil splash though now again since warm, it doesn't because there's water vapor above it? And what if they were magnets boiling splashing and would all fall back down for sure since don't stick to the walls and all of them hit the walls sooner or later and get to bottom? I'd like to know. You could have water in a vacuum box powering you in the living room~
     
    Last edited: Nov 7, 2015
  11. Nov 8, 2015 #10
    heat_pipe.jpg
    Yes, you can, given hot and cold reservoir (sink) exist forever. Heat is a boundary phenomena. There should be a enough temperature difference to encourage perpetual cyclic change of phase, although possibility of changing phase happens also in an isotherm, but not that much compared to sensible heat.
    Above photo is a heat pipe, which partially evacuated and filled with a volatile media.
     
  12. Nov 8, 2015 #11
    QUOTE="Ronie Bayron, post: 5282379, member: 576428"] heat_pipe.jpg
    Yes, you can, given hot and cold reservoir (sink) exist forever. Heat is a boundary phenomena. There should be a enough temperature difference to encourage perpetual cyclic change of phase, although possibility of changing phase happens also in an isotherm, but not that much compared to sensible heat.
    Above photo is a heat pipe, which partially evacuated and filled with a volatile media.[/QUOTE]

    I think he means can it boil forever without introducing a temperature difference. Just room temperature. In other words, I believe he is asking if there any other way to effect the condensation of the water vapor besides direct cooling from a heat sink. One way might be to evaporate room temperature water from the outside of the closed container which carries away heat and lowers the temperature thus condensing the steam. But then you need to provide a constant source of water to evaporate. This is how the Drinking Bird toy works. It uses room temperature water to evaporativity cool the liquid with respect to the ambient air which heats it. BTW, that's a very nice graphic. Thanks.
     
    Last edited: Nov 8, 2015
  13. Nov 8, 2015 #12
    Hey guys, I'm really good in science in many fields, I do indeed lack some understanding of this whole pressure temp. thing you's are talking about, but could you please explain to me what's wrong with this: If you have a metal box vacuum, with water at the bottom, it splash up boiling right? Wouldn't all of the water turn to vapor and hit into eachother making bigger droplets and fall back down and repeat boiling and splashing up in the vacuum? Or does it constantly boil splash and never stays at the bottom? I.e stays vapor now?
     
  14. Nov 9, 2015 #13

    CWatters

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    The water will eventually freeze unless heat is added from outside..

     
  15. Nov 9, 2015 #14
    But you have to not allow the water vapor to accumulate. Here it was pumped out and also the chamber was very large which implies even if it were not pumped out it would never have raised the pressure enough to stop the boiling yet the temperature keeps dropping as the water boils. In this case, I think if you kept the water at ambient through a thermal bath not under low pressure, it would all just boil away.
     
  16. Nov 9, 2015 #15
    It's good that you are smart. PVT_3D_diagram.png
    This topic is covered in Thermodynamics.
    I suggest further reading to grasp the main physical mechanism you want to comprehend.
     
    Last edited: Nov 9, 2015
  17. Nov 17, 2015 #16
    Boiling or Evaporation? Seems we are using terms as interchangable
     
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