Question

steam inside a closed vessel of fixed volume, 0.14 m^3. The steam exerts a pressure of 10 bar at 250 degrees Celcius. If the vessel is now cooled so that the pressure falls to 3.5 bar, determine the mass of the steam, the dryness fraction and the final temperature

Answer 1

Initial state is in the liquid-vapour saturation region since x₁ = 0.7

 

     $T = 350\degree C, P = 0.6 MPa v = 0.4742 m3/kg, u = 2881.2 kJ/kg$  

 

$T = 350 C, P = 0.8 MPa v = 0.3544 m3/kg, u = 2878.2 kJ/kg$

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 Final state: P₂ = 7 bars v₂m v₂ = 2v₁ = 0,3727 m³/kg

 

 steam is a superheated vapour at the final state. Interpolation is necessary!