♻️ Carnot cycle — η = 1 − T_C/T_H, and nothing beats it

Two isothermals (heat in at T_H, heat out at T_C) joined by two adiabatics form the Carnot cycle. Its efficiency depends ONLY on the two reservoir temperatures: η = 1 − T_C/T_H. No real engine between the same two temperatures can do better.

Walkthrough 1 / 5

Step 1 — isothermal expansion at T_H: the gas absorbs heat and does work (red leg).

Hot reservoir T_H 600 K

Cold reservoir T_C 300 K

η = 1 − T_C/T_H = — · heat in at T_H, heat out at T_C
steps 1&3 are isothermal (Q exchanged); steps 2&4 are adiabatic (Q = 0)

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