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Carnot engine
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The most efficient engine between two temperatures.
η = 1 − T_c/T_hThe most efficient reversible engine between T_h and T_c has η = 1 − T_c/T_h. No real engine can exceed it.
Between 600 K and 300 K: 50%.
Use kelvin; reaching 100% needs T_c = 0.
In more detail
The Carnot engine is an idealised reversible heat engine operating between two temperatures. Its efficiency, 1 minus Tc/Th, is the maximum possible for any engine between those temperatures.
Real-world uses
- Engineers use Carnot efficiency as an upper limit for real engines.
- Power plant designs aim to raise the hot temperature to improve efficiency.
- Engineers use the Carnot efficiency as the upper limit for any heat engine between two given temperatures.
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Frequently asked questions
Why is it the maximum?
Because any irreversible process produces extra entropy and lowers efficiency.
How can I raise the efficiency?
Increase the hot temperature or lower the cold temperature, in kelvin.
Why is the Carnot engine the best?
No real engine can exceed it, because it is reversible and operates between two fixed temperatures without any losses.
Related topics in Heat & Thermodynamics
Kelvin–Planck statement · Clausius statement · Heat engines · Carnot cycle · Refrigerators and heat pumps · Otto cycle