In thermodynamics, Carnot’s theorem, a corollary of Carnot’s principle, states that any two idealized (reversible) Carnot engines working between the same temperature differences (ΔT = TH - TC) will always have the same efficiency η :

\eta = \frac{\Delta T} {T_H}\

and that this is the maximum efficiency that any generalized heat engine can obtain. [1]

Notes
This heat engine efficiency theorem, sometimes called Carnot’s rule, is named after French physicist Sadi Carnot who described the theorem in his 1824 memoir Reflections on the Motive Power of Fire. Another theorem, in the field of mechanics, by the same name, is attributed to Lazare Carnot, Sadi Carnot’s father, which states that in any machine the accelerations and shocks of the moving parts all represent losses of moment of activity or of useful work done. [2]

References
1. (a) Perrot, Pierre. (1998). A to Z of Thermodynamics (Carnot's theorem, pgs. 33-35). Oxford University Press.
(b) Eu, Byung C. (2002). Generalized Thermodynamics: the Thermodynamics of Irreversible Processes and Generalized Hydrodynamics (4.1: Carnot’s Theorem, pgs. 32-33). Springer.
(c) Finn, Colin B.P. (1993). Thermal Physics (4.5: Carnot’s Theorem, pgs. 59-60). CRC Press.
2. (a) Dugas, Rene, and Maddox, J.R. (1988). A History of Mechanics (3. Carnot’s Theorem, pgs. 327-). Dover.
(b) Introduction by E. Mendoza in Reflections on the Motive Power of Fire, Dover, 1960.
(c) Carnot’s theorem – Wikipedia.

External links
‚óŹ Carnot's theorem (thermodynamics) - Wikipedia.

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