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Homework Help: Thermodynamic help (rankine)

  1. Dec 3, 2009 #1
    1. The problem statement, all variables and given/known data

    I am supposed to see if there is a feasibility of producing power in the 0.1-0.25 kW range. I am working with a thermosyphon Rankine power plant. It is an open ended design problem

    My question is that I am getting hung up on finding the mass flow rate. My professor says to treat it as an ideal Rankine cycle, but there is no work input at the pump stage (virtual pump). I have calculated the systems at each spot, so I have all enthalpy values, all temp and pressure values and all entropy values at each station.

    2. Relevant equations

    Qin/m = h1-h4
    Qout/m = h2-h3
    Wp/m = h4-h3
    Wt/m = h1-h2
    Wcycle = m[(h1-h2)-(h4-h3)] = m[Wt/m-Wp/m]

    3. The attempt at a solution

    I have calculated Qin/m, and Qout/m. But I am confused as how to calculate Wcycle (net power). Because m is in the way, I cannot compare the value I get of Wcyc/m. So my question is, is m a value I need to compose on my own since it is open ended, or is there a way I am forgetting to calculate it? If I do need to make my own value, how do I come up with that value?
  2. jcsd
  3. Dec 3, 2009 #2


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    Homework Helper

    You're correct in that you can only calculate Wcycle/m. If you have twice as much of the substance, the engine will do twice as much work.

    So: what does m/t need to be, in order to generate 0.1 to 0.25 kW?
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