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Homework Help: Thermodynamic cycle

  1. Oct 10, 2005 #1
    Sorry about the double post, I had technical difficulties that I was working on and the title of my orginal post got screwed up.

    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]
    to
    [tex]p_{2} = ?[/tex]
    [tex]V_{1} = .2m^3[/tex]

    [tex]U_{2}-U_{1}=0[/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]p_2=\frac{p_1V_1}{V_2}[/tex]

    [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.
     
  2. jcsd
  3. Oct 10, 2005 #2

    Andrew Mason

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    Homework Helper

    The work done between 2-3 is just [itex]P_2\Delta V = P_2(V_3-V_2) = P_2(7*V_2)[/itex]

    The change in internal energy is [itex]U_3-U_2 = U_3-U_1[/itex], since [itex]U_2=U_1[/itex]

    Use [itex]\Delta Q = \Delta U + W[/itex] to find the energy (heat) flow into the system.

    AM
     
    Last edited: Oct 11, 2005
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