1. The efficiency of an irreversible,
i.e. a real, heat engine is always less than the efficiency of a reversible one operating between the
same two reservoirs. hth, irrev < hth, rev
2.
2. The efficiencies
of all reversible heat engines operating between the same two thermal reservoirs are the same. (hth, rev)A= (hth, rev)B
3.
• Both of the
above statements can be demonstrated using the second law (K-P statement and C-statement). Therefore, the Carnot heat engine defines the maximum efficiency any practical heat engine can (hope
to) achieve. (see YAC: 5.8, for proof)
• Thermal
efficiency hth=Wnet/QH=1-(QL/QH)=f(TL,TH)
•In the next slide we will show that hth=1-(QL/QH)=1-(TL/TH).
•This relationship is often called the Carnot efficiency since it is
usually defined in terms of a Carnot Heat
Engine .