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Homework Help: Pressure calculation inside tank

  1. Sep 2, 2010 #1
    1. The problem statement, all variables and given/known data
    A rigid tank of volume 83 m3 contains 100 kg of H2O at 100oC. The tank is heated until the temperature inside reaches 120oC. Determine the pressure inside the tank at (a) the beginning and (b) the end of the heating process.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 2, 2010 #2


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    Staff: Mentor

    What do you know about water at 100 deg C?

    What do you know about water at 120 deg C?
  4. Sep 3, 2010 #3
    Hi Borek

    In the saturated steam table based on temperature, we can read the thermodynamic data of water at 100 Cel and 120 Cel.Then using the 1st law, we can calculate the heat energy from the data. But the problem is more related to heat transfer. The original situation is that I have a rigid and closed cylindrical vessel, of known dimessions, filled with some amount of water(mass = m) upto some height, in which the inside temperature is raised from room temperature to 100 Cel in some time. I want to calculate the vapor pressure over the water surface at that temperature which can be related to height of water coloumn.

    The cylinder is heated in oven. Suppose total volume inside cylinder was V and that of water was V0.

    Total energy supplied to cylinder from oven is

    E = Energy given to liquid of volume V0 + energy given to vapor of volume (V-V0) and density d + latent heat energy to convert d(V-V0) mass to vapor.

    I am not able to quantify these entities for calculation. I need some guidance for this.
  5. Sep 3, 2010 #4


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    Staff: Mentor

    I don't know the original problem then, but I have a feeling you may be overcomplicating things - if you have a steam data table, you can read the pressure - and that's all. The only possible problem is if 100 kg of steam is not enough to fill up 83 cubic meters of the tank for a given pressure - but then it is just an ideal gas type problem.

    Or am I missing something?
  6. Sep 4, 2010 #5
    No, actually all the water is not vaporized during the span of heating. some part of water becomes steam and rest remains liquid. since the container is rigid and sealed, the steam remains inside the container, over the liquid water, and exerts some pressure on it. I want to know that pressure.
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