tendency found in all isolated composite systems. Even if a Carnot heat engine is
used to operate isentropically by absorbing heat from the hot part of the system and
rejecting heat to the cold part, that such operation is possible is derived from the
spontaneity of the system. This can be seen clearly in particular in Case (d) above:
Compare the spontaneous event and the reversible event. As the end states of the
reversible event are the same as the spontaneous isolated event, it is clear that the
system in the reversible event gives out no heat and, thus, the produced work is
derived from heat from the heat reservoir at 539.901 K. The erstwhile isentropic
process produced work is effectively the “extracted heat” that the system is able to
extract from the reservoir during the second part of the reversible event.
Though this is a subtler example than that shown in Fig. 8.3, it demonstrates the
same case of conversion of extracted heat 100% into work driven purely by entropy
growth potential. (From a practical point of view, there is no reason to employ a
heat reservoir with temperatures lower than 539.901 K (in this case) if the purpose
is solely work production. Heat reservoirs are used here for the purpose of theoretically comparing the spontaneous event to the reversible events.)
These thought experiments, including that of Sect. 5.10, confirm that Eq. (130)
is applicable to isolated systems. The significance of that is that whereas the theory
of exergy at its current stage is formulated only for systems tending to equilibrium
with a surrounding reservoir. The extension of exergy analysis to isolated systems
tending to internal equilibrium will require further formulation involving complications associated with the treatment of composite systems. The present approach,
Eqs. (123) and (130), applies to both cases of external and internal equilibriums
based on the single conceptual set of entropy growth/entropy growth potential (see
next section). The parsimony of the present approach shows heuristic, as well as
conceptual, value in entropy growth potential discussed below.
8.5 The Entropy Growth Potential Principle
We have come to the vantage point to identify the ingredient, entropy growth
potential, for replacing universal interconvertibility.
Why did the MTH need the universal interconvertibility principle? Recall again
that thermodynamics was the study of heat and heat engines. While the Carnot–
Kelvin formula provided the specific idea of maximum possible mechanical work to
be derived from heat under one particular idealized condition, the principle provided the general idea of where mechanical work is to be derived in heat engines
from heat under general conditions, i.e., it provided the “conceptual” framework for
heat’s apparent utility. The theory of exergy then extended that into
energy-as-the-driver, without, however, challenging the principle itself.
210
8 The Second Law: The Entropy Growth Potential Principle …
used to operate isentropically by absorbing heat from the hot part of the system and
rejecting heat to the cold part, that such operation is possible is derived from the
spontaneity of the system. This can be seen clearly in particular in Case (d) above:
Compare the spontaneous event and the reversible event. As the end states of the
reversible event are the same as the spontaneous isolated event, it is clear that the
system in the reversible event gives out no heat and, thus, the produced work is
derived from heat from the heat reservoir at 539.901 K. The erstwhile isentropic
process produced work is effectively the “extracted heat” that the system is able to
extract from the reservoir during the second part of the reversible event.
Though this is a subtler example than that shown in Fig. 8.3, it demonstrates the
same case of conversion of extracted heat 100% into work driven purely by entropy
growth potential. (From a practical point of view, there is no reason to employ a
heat reservoir with temperatures lower than 539.901 K (in this case) if the purpose
is solely work production. Heat reservoirs are used here for the purpose of theoretically comparing the spontaneous event to the reversible events.)
These thought experiments, including that of Sect. 5.10, confirm that Eq. (130)
is applicable to isolated systems. The significance of that is that whereas the theory
of exergy at its current stage is formulated only for systems tending to equilibrium
with a surrounding reservoir. The extension of exergy analysis to isolated systems
tending to internal equilibrium will require further formulation involving complications associated with the treatment of composite systems. The present approach,
Eqs. (123) and (130), applies to both cases of external and internal equilibriums
based on the single conceptual set of entropy growth/entropy growth potential (see
next section). The parsimony of the present approach shows heuristic, as well as
conceptual, value in entropy growth potential discussed below.
8.5 The Entropy Growth Potential Principle
We have come to the vantage point to identify the ingredient, entropy growth
potential, for replacing universal interconvertibility.
Why did the MTH need the universal interconvertibility principle? Recall again
that thermodynamics was the study of heat and heat engines. While the Carnot–
Kelvin formula provided the specific idea of maximum possible mechanical work to
be derived from heat under one particular idealized condition, the principle provided the general idea of where mechanical work is to be derived in heat engines
from heat under general conditions, i.e., it provided the “conceptual” framework for
heat’s apparent utility. The theory of exergy then extended that into
energy-as-the-driver, without, however, challenging the principle itself.
210
8 The Second Law: The Entropy Growth Potential Principle …