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Homework Help: Thermodynamic cycle problem

  1. Oct 10, 2005 #1
    I'm having problems getting started on this one.

    A gas undergoes a thermodynamic cycle consisting of 3 processes

    process 1-2 compression with pressure(p)*volume(V) = constant, from
    [tex]p_{1} = 1 bar[/tex]
    [tex]V_{1} = 1.6m^3[/tex]
    [tex]p_{2} = ?[/tex]
    [tex]V_{1} = .2m^3[/tex]


    process 2-3
    Constant pressure to [tex]V_{3}=V_{1}[/tex]

    process 3-1
    Constant Volume, [tex]U_{1}-U_{3} = -3549kJ[/tex]

    There are no significant changes in kinetic or potential energy.
    Determine the heat transfer and work for process 2-3 in kJ.

    I don't have any problems finding[tex]p_{2}[/tex] or the work needed to compress the gas, but I'm not really sure where to go from there.


    [tex]W=\int p dV[/tex]

    When I work these out, I end up with 333kJ for W and 8 bar for p2.

    If someone could give me a quick push in the right direction, that would be great.
    Last edited: Oct 10, 2005
  2. jcsd
  3. Oct 17, 2005 #2

    Tom Mattson

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    Staff Emeritus
    Science Advisor
    Gold Member

    Sorry for the late reply. In case you're still interested, here are some questions for you to think about. If you answer them in order, you'll be led straight to the solution.

    * What is the net change in internal energy for the entire cycle?
    * What is the net change in internal energy for the process [itex]2\rightarrow 3[/itex]?
    * What is the work done for the process [itex]2 \rightarrow 3[/itex]?
    * Now use the First Law to get the heat transferred in the process [itex]2 \rightarrow 3[/itex].
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