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Homework Help: Polytropic processes on a PV plot

  1. Nov 14, 2011 #1
    1 -> 2 : Isochoric heat addition
    2 -> 3 : Polytropic expansion
    3 -> 1 : Isobaric compression back to the initial state

    Sketch this cycle on a pressure-volume plot in relation to the saturation curve.
    Now, my question is, why is the polytropic process on the PV plot concave up and not down, as shown on http://imageshack.us/photo/my-images/685/unledmhi.png/ ?
  2. jcsd
  3. Nov 15, 2011 #2

    Andrew Mason

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    The plot of the polytropic process depends on the value of n in [itex]PV^n = K[/itex]. If n = Cp/Cv it is an adiabatic process. If n = 1 then it is an isothermal process (PV = nRT = constant). If n=0 it is an isobaric process. None of those will provide a convex PV graph.

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