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A Efficiency of Irreversible Engine

  1. Feb 25, 2016 #1
    I have a small confusion that can an irreversible engine have greater efficiency than reversible engine if both have different source and sink temperatures?I know that under same conditions reversible engines are more efficient but what can be concluded under different conditions like both engines have different source and sink.
     
  2. jcsd
  3. Feb 25, 2016 #2

    jbriggs444

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    If you measure "efficiency" in terms of amount of usable energy harvested per unit of heat transferred then, yes, an irreversible heat engine operating on reservoirs with a large temperature ratio can be more "efficient" than a reversible heat engine operating on reservoirs with a temperature ratio closer to 1:1.
     
  4. Mar 2, 2016 #3
    If you consider efficiency(η) in terms of ratio of heat energy converted to work per heat energy derived from source. Then efficiency of reversible engine will always be 1, whereas in irreversible engine, the total heat energy will not be able to convert to work, since there may be many chances where heat derived may be dissipated. So the efficiency of irreversible engine(η) will between 0< η <1. Whatever be the temperatures.
    It means, η(r) > η(I)
     
  5. Mar 2, 2016 #4
    This is at odds with what jbriggs444 said in his post. Also, according to the definition that you gave, it is well known that the efficiency of a reversible engine operating in a cycle is less than 1.

    I therefore agree with jbriggs444.
     
  6. Mar 2, 2016 #5
    Based on the jbriggs444 definition, a reversible engine uses maximum amount of heat energy to work per unit of heat transferred, whereas in irreversible engine it uses less heat energy per unit heat energy transferred. In general efficiency of reversible engines is always greater than irreversible engine.
     
  7. Mar 2, 2016 #6

    jbriggs444

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    That is correct if the comparison is fair. But the original post here contemplated a comparison where the irreversible engine can be given an unfair advantage -- working from a pair of reservoirs with a different temperature difference.
     
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