In 1824, a French engineer and physicist, Nicolas Léonard Sadi Carnot advanced the study of the second law by forming a principle (also called Carnot’s rule) that specifies limits on the maximum efficiency any heat engine can obtain. In short, Carnot’s principle states that the efficiency of a thermodynamic cycle depends solely on the difference between the hot and cold temperature reservoirs.
Carnot’s principle states:
- No engine can be more efficient than a reversible engine (Carnot heat engine) operating between the same high-temperature and low-temperature reservoirs.
- The efficiencies of all reversible engines (Carnot heat engines) operating between the same constant temperature reservoirs are the same, regardless of the working substance employed or the operation details.
The formula for this maximum efficiency is:
- is the efficiency of the Carnot cycle, i.e., it is the ratio = W/QH of the work done by the engine to the heat energy entering the system from the hot reservoir.
- TC is the absolute temperature (Kelvins) of the cold reservoir,
- TH is the absolute temperature (Kelvins) of the hot reservoir.