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Carnot efficiency

The Carnot efficiency is the highest possible efficiency a heat engine can have while operating between two given temperatures, and applies only to an ideal, reversible engine. No real engine can exceed it, so it serves as a sanity check on a calculated efficiency.

\eta_{Carnot} = 1 - \dfrac{T_C}{T_H}

Carnot efficiency, temperatures in kelvin

Symbols

$T_H$	temperature of the hot reservoir	K
$T_C$	temperature of the cold reservoir	K

Example

An engine operates between $T_H = 600$ K and $T_C = 300$ K. $\eta_{Carnot} = 1 - 300/600 = 0.50$ , so at most 50%.

If a calculated efficiency exceeds the Carnot limit, something is wrong – no real engine can exceed it.

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