Carnot efficiency

Around the reversible cycle of the Carnot engine the ideal gas is returned exactly to its original state. For the Carnot engine the change in entropy DS around the cycle must be zero.

The efficiency of any engine is defined as the work output, DW, over the heat input, Q2. Note: Q2 is the heat that must be paid for. For a Carnot engine with zero entropy change, the efficiency is given by....

... where T is the temperature in Kelvins.

The efficiency of a Carnot Engine is always less than 1, (unless the temperature of the cold reservoir, T1, is zero Kelvin, which cannot be realized in practice).

It can be shown that the efficiency of all real engines is less than that of the ideal Carnot engine.

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