2. Out-of-balance behavior

2.1 Irreversible processes

The behavior of the working fluid during the transformations that take the system from an initial to a final state is not revealed by the preceding considerations. In particular, the irreversible physical processes that characterize the non-equilibrium behavior of the fluid during operation of the thermodynamic machine are not explained. On a macroscopic scale, the equilibrium state is defined by a set of extensive variables denoted X _i . It is customary to consider, following Callen