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Homework Help: [Thermodynamics I] Adding heat to a closed, rigid tank

  1. Feb 6, 2009 #1
    1. The problem statement, all variables and given/known data
    A closed, rigid tank contains 2kg of water initially at 80 degrees C and a quality of .6. Heat transfer occurs until the tank contains only saturated vapor at a higher pressure. Kinetic and potential energy effects are negligible. For the water as the system, determine the amount of energy transfer by heat, in kJ.


    2. Relevant equations
    U = Q - W, W = 0 => U = Q
    mu = U
    pv = RT

    3. The attempt at a solution
    I don't really know where to even begin. I know the volume is constant, and I assume that I need to find the specific internal energy for the water and water vapor at the initial and final temperatures. Given the initial temperature and knowing V is constant, I might be able to determine pressure? I can't figure out how I would find the temperature and pressure for the saturated water vapor state either.
     
  2. jcsd
  3. May 5, 2011 #2
    hi, the question has given mass as 2kg, this helps in finding results from the sp. volume/sp.enthalpy from the steam tables..at 80C find hf & hg and similarly for sp.volume along with the quality, find the total enthalpy and volume at 80C, then, since, its a closed tank, the volume of matter remains the same but changes from liquid-vapour mixture to vapour condition. At, sat. vapour condition, only vapour remains but the volume remains the same which was found at 80C and with this volume, using steam tables look to match identical volumes in the superheated steam tables-might require interpolation..
     
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