Nicolas-Leonard-Sadi Carnot, French engineer, founder of the science of thermodynamics. 1796 - 1832

Born in Paris, 1st June 1796, Sadi Carnot was born into a France still in recovery, in the post-Revolution years. His father, Lazare Carnot was a noted Revolutionary figure, and the first few years of his life were marked by turmoil, his family forced into exile, only to return again in 1799 when his father was appointed by Napoleon as Minister of War.

Following his forced resignation, his father turned his attention to educating his son. He was ideally placed to carry out this task, having wide knowledge of mathematics, mechanics, as well as political and military experience. in 1812, Sadi was accepted into the École Polytechnique, graduating in 1814. During this time, Paris was under attack, and he, with many fellow students, was involved in the defence of the city.

He also attended the École Genie in Metz, received an officer's commission and became an engineer in the Army, initially involved in the inspection of fortifications, but returning to Paris in 1819. He remained a soldier most of his life, despite disagreements over promotion and his job role. He effectively retired from the regular army in 1820, but remained on call as a reserve.

Ever curious about scientific and engineering matters, he attended many public lectures on the sciences, and was befriended by the physicist and industrialist Nicolas Clément-Desormes. He was later to expand on many of Clément-Desormes theories. Because of his mentor's interest in steam engines (then the driving force behind industry), he began to consider ways of improving their efficiency.

He had seen advanced engines, and set about examining what made the imported British engines superior. Rather than look at purely technical details, he looked at the essence of the problem. In his 1824 essay Reflections on the Motive Power of Fire, he noted that power was produced when heat drops from the higher temperature of the boiler to the lower temperature of the condenser. Despite working on the incorrect assumption that heat was some form of gas, a theory popular at the time, his predictions were correct. In particular, he was right in his statement that the efficiency of an idealised, frictionless engine depended only on the highest and lowest temperatures, and not on the mechanics or medium of heat transmission. His formula describes the maximum amount of heat convertible into work:

(T1 – T2)/T2 where T1 is the temperature of the hottest part of the machine and T2 is the coldest part.

Following this, he continued to work, not just in the design and construction of steam engines, and improving public education. He died in Paris on 24th August, 1832 of cholera.

His theories and findings were mostly ignored, largely because the British engineers were so highly regarded that no-one would believe that their work could be improved upon in France. However, 1834 saw a change in fortune for Carnot's theories, when Émile Clapeyron the railway engineer began to publicise his work on the Carnot cycle. His theories were then quickly accepted, and became incorporated into the general theories of thermodynamics developed by Rudolf Clausius and Lord Kelvin.

Encyclopædia Britannica

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