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Condensation in vacuum

  1. Nov 11, 2014 #1
    Hi

    I have been thinking about this idea and i'we come to the conclusion that i need to discuss this with someone who has a better understanding of physics than i have.
    First off, let me help you visualize it:

    You put pieces of hardware that generate heat inside of a container, the container has a thermoelectric motor wich tries to keep the insides of the container at 20 degrees celsius, like a fridge, but the container itself is vacuum sealed.

    Would there be any condensation inside of the container?
     
  2. jcsd
  3. Nov 11, 2014 #2

    Bandersnatch

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    Hi Maun, welcome to PF!

    Do you mean there is vacuum inside? If yes, then there's nothing to condense, by the definiton of vacuum.
     
  4. Nov 11, 2014 #3
    Thank you for the fast reply.
    Would there still be no condensation if the containers temperature would go below 0 degrees?
     
  5. Nov 11, 2014 #4

    Bandersnatch

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    But what do you want to condense? There needs to be some gas molecules inside first.
     
  6. Nov 11, 2014 #5

    russ_watters

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    And how can the inside be at 20C if it is a vacuum? This doesn't make sense to me. Are you vacuum sealing food? Those aren't much of a vacuum.
     
  7. Nov 11, 2014 #6
    What would the temperature be inside of a vacuum then?
     
  8. Nov 12, 2014 #7

    Bandersnatch

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    What russ is talking about is the fact that temperature actually has a meaning of "average kinetic energy of particles". With no particles to speak of, as in vacuum, it makes no sense to speak of temperature of the inside of the box.
    However, one could talk about the temperature of the walls of the box, and the thermal radiation filling the inside space. Still, the distinction needs to be made clear - for vacuum the concept of temperature stops making sense.

    Back to condensation - for condensation to occur, first there has to be some gas to condense (which means change into its liquid phase). Then the combination of pressure and temperature must be within certain limits. If the pressure is too low, as you lower the temperature you'll see that the gas never condenses and instead resublimates (i.e., changes directly into a solid). For water vapour this occurs at about 1% of the standard atmospheric pressure. If your vacuum is better than that, there will be no condensation no matter how cold the walls of the container get - but there will be frosting.
    It works similarly for other atmospheric gases.
     
    Last edited: Nov 12, 2014
  9. Nov 12, 2014 #8

    sophiecentaur

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    To be fair, the container would be at a Temperature, however many odd molecules there might be buzzing around inside the container. Their velocity distribution would correspond to the container temperature.

    Obtaining very high vacua is highly technical because you can expect molecules of all sorts of stuff on the surfaces of the containers / tubing / pump etc..
    Even out in the deepest space, you can expect one proton in every metre cube - not to mention the virtual particles that come and go - so there is no real point in trying to discuss a 'perfect' vacuum.
     
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