Carnot heat engine

A Carnot heat engine is a theoretical engine that runs on the Carnot cycle, a sequence of reversible thermodynamic processes. French military engineer Nicolas Leonard Sadi Carnot proposed the model in 1824 as the most efficient heat engine theoretically possible, with its efficiency set entirely by the absolute temperatures of its hot and cold reservoirs rather than by any particular working substance or design. The engine transfers energy from a warm reservoir to a cool one and converts part of that energy into mechanical work; run in reverse, the same cycle describes a refrigerator or heat pump. As a theoretical construct it is not a practical device but a benchmark against which real engines are measured. Carnot's analysis, though built on the later-discredited caloric theory of heat, directly led to the second law of thermodynamics and the concept of entropy once physicists such as Rudolf Clausius and William Thomson reworked its foundations.