Sadi Carnot: Founder of Thermodynamics
Sadi Carnot
(1796–1832)
Nicolas Léonard Sadi Carnot (June 1, 1796 – August 24, 1832), usually called Sadi Carnot, was a French physicist and engineer who pioneered the study of thermodynamics. He is recognized today as the founder of thermodynamics.
Family and Early Life
He was the son of Lazare Carnot, known as the “Great Carnot,” and uncle of Marie François Sadi Carnot, who became President of the French Republic.
Reflections on the Motive Power of Fire
After graduating from the École Polytechnique in 1824, Carnot published Reflections on the Motive Power of Fire and on Suitable Machinery to Develop This Power, which outlined the first two principles of thermodynamics. This work, little understood by his contemporaries, was later rediscovered in Germany by Rudolf Clausius (who disseminated it) and William Thomson (Lord Kelvin) in the United Kingdom. In recognition of Carnot’s contributions, the second law of thermodynamics is often called the Carnot-Clausius principle. This principle allows us to determine the maximum efficiency of a heat engine depending on the temperatures of its hot and cold reservoirs.
Carnot’s Discoveries
When Louis XVIII sent Carnot to England to investigate the high performance of their steam engines, he realized the widespread belief that raising the temperature as much as possible improved the operation of steam machinery. Shortly after, he discovered a relationship between the temperatures of the hot and cold reservoirs and machine performance. As a corollary, it follows that no real machine can reach the theoretical efficiency of a Carnot engine (obtained according to the Carnot cycle), which is the maximum possible for that temperature range. A machine that follows this Carnot cycle is known as a Carnot engine.
Later Years and Legacy
Sadi Carnot published nothing after 1824 and probably believed himself to have failed. His thinking was original and unique in the history of modern science because, unlike many other scientists, it was not based on anything prior and opened a wide field of research. His book, initially neglected by the scientific community, was later used by Rudolf Clausius and Lord Kelvin to establish, in a mathematical way, the foundations of thermodynamics.