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Homework Help: Heat engine

  1. Feb 5, 2010 #1
    1.A heat engine is rejecting 200btu/h and 30% efficient, how much power does it use in watts?

    2. QH=w+QC and power=energy/time (1kwh=3412btu)
    and a power diagram: QC= wasted heat, w=work


    3. 200btu/h(1kwh/3412btu)(1000w/1kw)=58.6watts (30%)=17.6watts
    This value just seems too small??
  2. jcsd
  3. Feb 5, 2010 #2


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    Homework Helper

    It is too small, but not by much. You're multiplying 58.6% watts, which is the waste heat produced by the heat engine, by efficiency. You need to multiply total energy output (work+waste heat) by efficiency to get the answer.
  4. Feb 5, 2010 #3
    Your saying:

    Work=17.6watts +waste heat=58.6watts---=76.2watts total

    then 76.2watts (x) eff.=30%----=17.9watts used power??

    Is this right??
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