The Carnot Principles
- The efficiency of an irreversible heat engine is always less than the efficiency of a reversible one operating between the same two reservoirs. hth, irrev < hth, rev
- The efficiencies of all reversible heat engines operating between the same two reservoirs are the same. (hth, rev)A= (hth, rev)B
- Both 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 reach up to.
- Thermal efficiency ?th=Wnet/QH=1-(QL/QH)=f(TL,TH) and it can be shown that ?th=1-(QL/QH)=1-(TL/TH). This is called the Carnot efficiency.
- For a typical steam power plant operating between TH=800 K (boiler) and TL=300 K(cooling tower), the maximum achievable efficiency is 62.5%.