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Stored Energy in a pressure vessel

  1. Jan 19, 2009 #1
    Consider a problem where a tank holds compressed natural gas, compressed to approx. 250 times atmospheric conditions.

    Now release the tank valve letting some of the gas out.

    Assuming a small timestep, I can approximate the energy lost as 1/2 mv^2,

    where m is the mass released during the timestep, and v is the (assumed constant for small timestep) velocity of exiting gas.

    Can I equate this to the change in stored energy in the tank during this timestep with reasonable accuracy?

    If so, can I model the stored energy as E = PV

    where P is pressure in the tank and V is the volume.

    Thanks alot.
  2. jcsd
  3. Jan 19, 2009 #2


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  4. Jan 19, 2009 #3
    I think the difference is that I was assuming an isochoric process, since a tank of fixed volume held the process. Maybe this is not the case? Either way, it should be noted that in my case I am just looking for a valid approximation, so I do not wish to model a differential problem. I have been using timesteps.

    So if isochoric is assumed

    Work = PdV = 0

    But I am looking at stored energy, not work done, this is where I am confused.
    Last edited: Jan 19, 2009
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