Nicolas Leonard Sadi Carnot

Nicolas Léonard Sadi Carnot , 1796-1832, French physicist, a founder of modern thermodynamics; son of Lazare N. M. Carnot. His famous work on the motive power of heat ( Réflexions sur la puissance motrice du feu, 1824) is concerned with the relation between heat and mechanical energy. Carnot devised an ideal engine in which a gas is allowed to expand to do work, absorbing heat in the process, and is expanded again without transfer of heat but with a temperature drop. The gas is then compressed, heat being given off, and finally it is returned to its original condition by another compression, accompanied by a rise in temperature. This series of operations, known as Carnot's cycle, shows that even under ideal conditions a heat engine cannot convert into mechanical energy all the heat energy supplied to it; some of the heat energy must be rejected. This is an illustration of the second law of thermodynamics. Carnot's work anticipated that of Joule, Kelvin, and others.

Carnot, (Nicolas Léonard) Sadi (1796–1832) French engineer and physicist whose work laid the foundation for the science of thermodynamics. His major work, Réflexions sur la puissance motrice du feu (1824), provided the first theoretical background for the steam engine and introduced the concept of the second law of thermodynamics (involving entropy), which was formulated later by Rudolf Clausius. Carnot's work was extended in 1834 by the railway engineer Emile Clapeyron and recognized in 1848 by William Kelvin.