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Homework Help: Steam Power plant (Reheat)

  1. Apr 17, 2017 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    Heat added, Qa (This I'm not sure how since the steam passed through a reheater before it enters the HPT. That is what I understand based on the problem above)
    Work Net, Wnet
    Efficiency, Wnet/Qa
    Heat Rate, WP/EP (Not sure if that is the correct formula)

    3. The attempt at a solution
    First I made a T-S Diagram

    Based on the diagram above, I got all these enthalpy values.
    h1 = h @ 3 MPa & 370C
    h2 = h @ 0.7 MPa & s1
    h3 = h @ 0.7 MPa & 500C
    h4 = hf4 +x hfg4 (All values, 0.007 MPa)
    where x = (s4 - sf4)/sfg4
    h5 = hf @ 0.007 MPa
    h6 = vf5 (P6-P5)
    WP1 = h6-h5
    ha = h @ 3 MPa and 500C

    The WNet that I got is, 1485.491
    For the Qa = (ha-h6) + (h3-h2) = 3959.022

    Eff = .3752

    Was not able to solve Heat Rate.

    I can't seem to understand how the answers shown in the problem was got. Please enlighten me. Thanks in advance!
  2. jcsd
  3. Apr 17, 2017 #2
    It looks to me like h3 is wrong. It should be equal to h2 plus the heat given up by the high pressure stream between 500 C and 370 C. So, it should be about 3100 J/kg.
  4. Apr 17, 2017 #3
    Thank you for your reply.
    Should I get the heat given up by using this formula?
  5. Apr 18, 2017 #4
    Sure. Or you can get it from the steam tables as the ##\Delta h##. Both should give about the same answer.
  6. Apr 18, 2017 #5

    We was informed that the label in the schematic diagram that was given to us was wrong. I adjusted my TS diagram based on the correction and tried to solve it again. Thankfully I got the answers now.

    Thank you very much for your replies.
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