The basics of thermodynamics were stated by Sadi Carnot in 1824. He considered a heat engine which operates by drawing heat from a source which is at thermal equilibrium at temperature T h o t , and delivering useful work. Carnot saw that, in order to operate continuously, the engine requires also a cold reservoir with the temperature T c o l d , to which some heat can be discharged. By simple logic he established the famous ‘’’Carnot Principle’’’ : ‘’No heat engine can be more efficient than a reversible one operating between the same temperatures’’.