Second law efficiency

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written 7.9 years ago by

teamques10 ★ 65k

Thermal efficiency and the coefficient of performance for devices is a measure of their performance.
They are defined on the basis of the first law only, and they are sometimes referred to as the first-law efficiencies.
The first law efficiency, however, makes no reference to the best possible performance, and thus it may be misleading.
Second-law efficiency is defined as the ratio of the actual thermal efficiency to the maximum possible (reversible) thermal efficiency under the same conditions.

$$η_Π = \frac{η_{th}}{η_{threv}} ........ (For Heat Engine)$$
The second-law efficiency can also be expressed as the ratio of the useful work output and the maximum possible (reversible) work output. $$η_Π = \frac{W_U}{W_{rev}} ......(For Work Producing device)$$
For cyclic devices such as refrigerators and heat pumps, it can also be expressed in terms of the coefficients of performance as: $$η_Π = \frac{COP}{COP_{rev}}....(For refrigerator and heat pumps)$$

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