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Homework Help: Thermodynamics question - is this right?

  1. May 17, 2006 #1
    Suppose a power plant delivers energy at 980 MW using steam turbines. The steam goes into the turbine superheated at 625 K and deposits its unused heat in river water at 285 K. Assume that the turbine operates as an ideal Carnot engine. If the river flow rate is 37 m^3 / s, estimate the average temperature increase of the river water immediately downstream from the power plant. What is the entropy increase per kilogram of the downstream river water in J / kg * K?


    What I've got so far, is this right?:

    e ideal = [ Th - Tl ] / Th = [625 - 285] / 625 = .544 (don't know if this has any relevance in the question being asked)

    density of water - 1000 kg / m^3

    flow of 37 m^3 / s times 1000 kg / m^3 = 37,000 kg / s

    980 MW = 980 MJ / s = 980000 kJ

    980 MW = flow (kg/s) * heat capacity (kJ / kg / degrees Celsius) * T (degrees Celsius)

    T = [980000 / (37000 * 4.186)] = 6.327 degrees Celsius ?
     
  2. jcsd
  3. May 17, 2006 #2

    Andrew Mason

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    The efficiency is .544 and the work output/unit time is 980 mW. So how much heat is drawn from the hot reservoir and how much is rejected to the cold reservoir? Use:

    [tex]Q_h - Q_c = W[/tex] and

    [tex]\eta = W/Q_h[/tex]

    AM
     
  4. May 17, 2006 #3
    Thank you.
     
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