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Steam generation thermodynamics

  1. May 1, 2017 #1
    a cylindrical tank with volume V
    a volume of water is inside the tank and the rest is air
    now if coal combustion is releasing heat into the tank Qin
    and when the gauge reads a certain pressure "P", the valve is opened which allows steam to exit the boiler
    what's the mass flow rate of the steam?
     

    Attached Files:

  2. jcsd
  3. May 1, 2017 #2
    Is this a homework problem?
     
  4. May 1, 2017 #3

    anorlunda

    Staff: Mentor

    The mass flow out will depend most strongly on the size of the valve and the outlet pipe. The flow rate will also vary with time.

    If that is homework, there is too little information given to solve it.
     
  5. May 1, 2017 #4
    I think they want him to assume that the rate of heating is constant.
     
  6. May 2, 2017 #5
    this is a part of a senior project that im working on.
    you can assume anything to simplify it
    assume it's a bachelor's degree level question
     
  7. May 2, 2017 #6
    What is your analysis of this so far?
     
  8. May 2, 2017 #7
    Ignore the previous question.
    now let's say that the tank is vacuumed and has a volume "Vt", and the valve is closed
    then a volume "Vw" of water at T1=20C is added to the tank
    water is heated using an external heat source (coal combustion) until its temperature reaches T2=120C
    what is the mass of steam generated in the tank, and when the valve is opened, what is the flow rate of steam? what is the pressure in the tank?
    assume the cross-sectional area of the pipe is "Ap" and ignore heat losses
     
  9. May 2, 2017 #8
    What are your thoughts on how this would be approached?
     
  10. May 2, 2017 #9
    after t seconds, the heat rate is:
    Qdot = mw . (cp2 . T2 - cp1 . T1) / t
    control volume thermodynamics
    Ein - Eout = dE/dt (assuming steady)
    Ein = Eout
    Qdot = mout . u2 -------eq1
    at T2=120C
    P2=gauge pressure reading just before opening the valve
    then from steam tables, we get u2 and substitute in eq1 to find mout
    and how do I find the amount of vapor generated after t seconds?
     
  11. May 2, 2017 #10
    Is this what you are asking: I have water in a constant volume tank, and I am supplying heat at a constant rate. When the pressure gets to a certain value, I start removing mass at a rate necessary to hold the pressure at this constant value, while continuing to supply heat?
     
  12. May 6, 2017 #11
  13. May 6, 2017 #12

    anorlunda

    Staff: Mentor

    The simplest solution makes use of energy conservation. Can you write expressions for the total energy in and the total energy out?
     
  14. May 6, 2017 #13
    Are you currently learning about the open system (control volume) version of the first law of thermodynamics?
     
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