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Homework Help: Thermodynamics - Steam

  1. Apr 18, 2009 #1
    The question MUST be very simple! it is a 3 mark question, the first question of a first year Mech. Eng. Thermodynamics exam...

    1. The problem statement, all variables and given/known data
    A boiler produces wet steam at a pressure of 8.5 bar. A sample of the steam is passed through a throttling calorimeter. At the calorimeter exit, it reads 2 bar, 141 ÂșC. Determine the dryness fraction (quality?) of the wet steam if the process is adiabatic.

    2. Relevant equations
    First Law : Q-W=E2-E1 (needed?)
    Steam Tables
    PV=RT (does it apply??)
    X= (v-vf)/(vg-vf)

    3. The attempt at a solution
    I am very confused as to how to use the steam table and where and when each applies. Also, I do not know where to find v, and if PV=RT applies in the superheated region.

    Any help is much appreciated.
  2. jcsd
  3. Apr 18, 2009 #2
    pv=rt is the ideal gas, its not applicable to steam in any way shape or form. Remember this for the rest of your thermo days.

    Remember throttles are isenthalpic.

    So use what you know about the steam to find an enthalpy at 8.5 bar. We know that as its a throttle its enthaply is the same at the lower pressure.

    Use this value of enthalpy to find the quality by interpolation.
  4. Apr 18, 2009 #3
    I'll give it a go! thanks a lot!
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