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Calculate pressure inside closed container

  1. Dec 20, 2013 #1
    A small container is filled with water (30ml). Next it is heated at 140°C. I need to determine the internal pressure caused by the heating process.

    The containers dimensions:
    height : 100mm
    Diameter: 39 mm
    Volume= circa 0,0203 m³

    First thing I did was to look it up at steamtables. For saturated steam at 140°C it corresponds to 0,3616 kPa.

    Now I was wondering how to bring the volume of the container in consideration. Intuitive I thaught, that an increase of volume of the container results in a decrease of pressure inside the container. So I was wondering how I could take the volume of the container in account with the data from the steamtables (I'm stuck at this point).

    I hope someone can help me on the way!

    kind regards
    Last edited: Dec 20, 2013
  2. jcsd
  3. Dec 20, 2013 #2
    The pressure would have to be higher than the equilibrium vapor pressure so that it could stay a liquid. The liquid would tend to thermally expand, so the pressure would have to be high enough to compressively offset the thermal expansion (and maintain the volume constant). If there were initially head space in the container, however, this would change everything.
  4. Dec 29, 2013 #3
    Well, there is a head space in the container. The container is filled approximately 1/3 with water, before the heating process starts. Is it correct to say that the absolute pressure is 3,6154 bar at 140°C, just reading the steam table (see attachment) ? Or am I wrong here ?

    Attached Files:

  5. Dec 29, 2013 #4
    You're absolutely correct. Just a small fraction of the liquid would have to evaporate to achieve this pressure in the vapor phase.
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