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Gibbs phase rule use for wet vapour

  1. Nov 6, 2016 #1
    I have a doubt regarding gibbs phase rule in thermodynamics.. It says the number of independent intensive properties required to specify the state of a system is F=C-P+2 where C is number of components and P is the number of phase.. So for a water and water vapour system, C=1, P=2 . So F=1. If we specify the temperature,pressure is fixed. But inorder to completely fix the state of the system, the dryness fraction should also be known. As the dryness fraction determines specific volume of the system. So 2 variables are required, which is not correct according to Gibbs phase rule. Am i making any mistake in this? Please help
     
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  3. Nov 10, 2016 #2

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    Not a variable in the sense you are using it.
     
  4. Nov 11, 2016 #3
    How? I can have different specific volumes based on different dryness fraction.
     
  5. Nov 11, 2016 #4

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    Can you?
     
  6. Nov 21, 2016 #5
    Yeah in in Pv diagram of water I have series of points on the horizontal line inside the vapor dome.
     
  7. Nov 21, 2016 #6

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    For application of the phase rule vapor is saturated or it is not; you don't have the option of looking at the average density of "wet steam." That is not a variable you can arbitrarily include in the degrees of freedom.
     
  8. Nov 25, 2016 #7
    I am getting your point but somehow I am not satisfied, can you please elaborate espicially your density logic.
     
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