Application of the Second Law of Thermodynamics to Energy Systems

The second law of thermodynamics has been applied to the analyses and optimizations of various energy systems. The increase of entropy principle-perhaps the most commonly used second-law statement-when applied to a composite thermodynamic system, is only a necessary, not a sufficient, condition for the second law to be satisfied. Negative entropy generation in some regions in a composite system may be cancelled by the positive entropy generation in other regions. In this case the total entropy generation of the system may be positive, but the second law of thermodynamics, which is a local and instantaneous law and should be satisfied everywhere and at ally instant, is violated in the regions of negative entropy generation.