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Thermodynamics - Energy analysis of piston-cylinder device

  1. Sep 25, 2007 #1
    Hello :)

    I'm having trouble working on this homework question (please see attachment). The answers are supposed to be
    a) 22.61 KJ
    b) 36.79 KJ
    c) 151.8*C

    I solved (a) and I noticed that the answer to (c) is that saturation temperature at 500kPa, but I just cannot get (b)! In fact, I'm not really sure I even know what's given for part (b). Obviously P=500kPa, but what else is known? Would Vb = 0.6(Va) = 0.0551898 m^3 ? It seems like I need another intensive property (other than P) to identify the state as a start.

    help :confused:

    Attached Files:

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  2. jcsd
  3. Sep 25, 2007 #2
    I just read the sticky about homework. Sorry.
  4. Sep 25, 2007 #3
    So I worked on it some more, just trying to understand the darn thing.. and yes, [tex]V_{b}[/tex] = 0.0551898 m^3. Now which formula to use for boundary work?

    For constant temp and an ideal gas, I know the formula:
    [tex]W_{b}[/tex] = [tex]\int[/tex][tex]mRT/V[/tex]dV = mRT*ln([tex]V_{2}[/tex]/[tex]V_{1}[/tex])

    But prof said that for real gases undergoing an isothermal process, the integral in the boundary work equation "would be done numerically." What does that mean??
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