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Help with Thermodynamics question- Carnot Power Cycle

  • 11-02-2014 10:16AM
    #1
    jeepers101
    Registered Users, Registered Users 2 Posts: 720 ✭✭✭


    Hi all,

    I'm seriously struggling with a couple of thermodynamics questions. Any help is greatly appreciated.



    Water having mass 1 kg is used in a closed system to execute the Carnot power cycle. During the isothermal heat intake process the water receives heat until it become saturated vapour from an initial state where the pressure is 15 bar and the dryness fraction is 25%. After the heat intake the vapour expands adiabatically to a pressure of 1 bar and dryness fraction of 84.9%

    a) calculate W and Q for the isothermal heat intake process by neglecting Vf

    b) Calculate W and Q for the expansion process which occurs between the end of the isothermal heat intake process and the beginning of the heat rejection process.



    From the thermodynamics tables I have:

    Vg = 0.1317m^3/kg

    Uf = 843Kj/kg

    Ug = 2595Kj/kg

    Calculating V1 & V2:

    V1 = 0.25(0.1317) = 0.032925m^3/kg

    V2 = Vg = 0.1317m^3/kg

    Calculating U1 & U2:

    U1 = 843+0.25(2595-843) = 1281Kj/kg

    U2 = Ug = 2595Kj/Kg


    After this I'm stumped.


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