Any thermodynamic working fluid (ideal gas in classical analysis)
efficiency formula
η_max = 1 − T_C / T_H
originator
Nicolas Léonard Sadi Carnot (1824)
applications
Theoretical upper bound for heat engines; reversed cycle models ideal heat pumps and refrigerators
Core Principles & Analysis
Formulated by French military engineer Sadi Carnot in his 1824 treatise 'Reflections on the Motive Power of Fire' and expressed graphically by Émile Clapeyron in 1834, the Carnot cycle alternates two isothermal heat-transfer processes with two reversible adiabatic (isentropic) processes.
By Carnot's theorem, no heat engine operating between a hot reservoir at absolute temperature T_H and a cold reservoir at T_C can exceed the Carnot thermal efficiency η = 1 − T_C / T_H, regardless of the working fluid.
On a temperature–entropy (T–S) diagram, the Carnot cycle traces a simple rectangle whose enclosed area T_H·ΔS − T_C·ΔS equals the net mechanical work output per cycle.