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81 Carnot, Nicolas Léonard Sadi
SUBJECT AREA: Steam and internal combustion engines[br]b. 1 June 1796 Paris, Franced. 24 August 1831 Paris, France[br]French laid the foundations for modern thermodynamics through his book Réflexions sur la puissance motrice du feu when he stated that the efficiency of an engine depended on the working substance and the temperature drop between the incoming and outgoing steam.[br]Sadi was the eldest son of Lazare Carnot, who was prominent as one of Napoleon's military and civil advisers. Sadi was born in the Palais du Petit Luxembourg and grew up during the Napoleonic wars. He was tutored by his father until in 1812, at the minimum age of 16, he entered the Ecole Polytechnique to study stress analysis, mechanics, descriptive geometry and chemistry. He organized the students to fight against the allies at Vincennes in 1814. He left the Polytechnique that October and went to the Ecole du Génie at Metz as a student second lieutenant. While there, he wrote several scientific papers, but on the Restoration in 1815 he was regarded with suspicion because of the support his father had given Napoleon. In 1816, on completion of his studies, Sadi became a second lieutenant in the Metz engineering regiment and spent his time in garrison duty, drawing up plans of fortifications. He seized the chance to escape from this dull routine in 1819 through an appointment to the army general staff corps in Paris, where he took leave of absence on half pay and began further courses of study at the Sorbonne, Collège de France, Ecole des Mines and the Conservatoire des Arts et Métiers. He was inter-ested in industrial development, political economy, tax reform and the fine arts.It was not until 1821 that he began to concentrate on the steam-engine, and he soon proposed his early form of the Carnot cycle. He sought to find a general solution to cover all types of steam-engine, and reduced their operation to three basic stages: an isothermal expansion as the steam entered the cylinder; an adiabatic expansion; and an isothermal compression in the condenser. In 1824 he published his Réflexions sur la puissance motrice du feu, which was well received at the time but quickly forgotten. In it he accepted the caloric theory of heat but pointed out the impossibility of perpetual motion. His main contribution to a correct understanding of a heat engine, however, lay in his suggestion that power can be produced only where there exists a temperature difference due "not to an actual consumption of caloric but to its transportation from a warm body to a cold body". He used the analogy of a water-wheel with the water falling around its circumference. He proposed the true Carnot cycle with the addition of a final adiabatic compression in which motive power was con sumed to heat the gas to its original incoming temperature and so closed the cycle. He realized the importance of beginning with the temperature of the fire and not the steam in the boiler. These ideas were not taken up in the study of thermodynartiics until after Sadi's death when B.P.E.Clapeyron discovered his book in 1834.In 1824 Sadi was recalled to military service as a staff captain, but he resigned in 1828 to devote his time to physics and economics. He continued his work on steam-engines and began to develop a kinetic theory of heat. In 1831 he was investigating the physical properties of gases and vapours, especially the relationship between temperature and pressure. In June 1832 he contracted scarlet fever, which was followed by "brain fever". He made a partial recovery, but that August he fell victim to a cholera epidemic to which he quickly succumbed.[br]Bibliography1824, Réflexions sur la puissance motrice du feu; pub. 1960, trans. R.H.Thurston, New York: Dover Publications; pub. 1978, trans. Robert Fox, Paris (full biographical accounts are provided in the introductions of the translated editions).Further ReadingDictionary of Scientific Biography, 1971, Vol. III, New York: C.Scribner's Sons. T.I.Williams (ed.), 1969, A Biographical Dictionary of Scientists, London: A. \& C.Black.Chambers Concise Dictionary of Scientists, 1989, Cambridge.D.S.L.Cardwell, 1971, from Watt to Clausius. The Rise of Thermodynamics in the Early Industrial Age, London: Heinemann (discusses Carnot's theories of heat).RLHBiographical history of technology > Carnot, Nicolas Léonard Sadi
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