Heat Engine

A heat engine converts thermal energy into mechanical or electrical work by moving a working substance between a hot source and a cold sink, extracting useful work from the flow between them while necessarily rejecting some heat to the cold sink rather than converting all of it. Devices exploiting the principle in a rough form have been known since antiquity, but heat engines only became practically important with the steam engines of the eighteenth century industrial revolution, well before their own thermodynamic theory existed. Sadi Carnot's 1824 analysis of the idealized heat engine, the Carnot cycle, established the theoretical ceiling on any real heat engine's efficiency, a limit set only by the temperatures it runs between and never exceeded by an actual device.