framework completing a full circle. We shall conclude that engineers find the utility
of energy in its exergetic content, i.e., the consideration of exergetic content of
energy is the only way to think in terms of energy intelligently. Another way to
appreciate usefulness in exergetic thinking is that, via the theory of exergy, a
quantitative linkage can be found (see below) between the Carnot–Kelvin formula
and Gibbs free energy, giving unity to the typical core knowledge of mechanical
engineering and typically what chemists and chemical engineers know. Furthermore, we shall find exergy analysis is particularly effective in application to
component processes (the unit operations level) instead of the whole-systems level,
and therefore it is a powerful tool in identifying the problem. Even though it, in
itself offers no solution, but identification of where a better solution is needed is
paramount.
7.2.2 Energy Equation for Open Systems
So far, our discourse has been focused on closed systems since the first law and the
second law are introduced naturally based on the consideration of closed systems.
This focus will continue in Chaps. 8 and 9. But, beginning with this chapter and in
Chap. 10, engineering application, i.e., engineering thermodynamics, will be the
main goal of our discourse. In the realm of engineering application, consideration
must be made to open systems, as many devices are open systems.
Beginning with the first law, Eq. (23), which is rewritten as
dE
dt
¼ _
Q À _
W
ð23BÞ
the first law equation is shown in Chap. 10 to be developed into an equation applied
to a control volume, cv, defining a device. Key assumptions and steps there (see
Chap. 10 for details) are reproduced here.
The system rate equation is related to expressions of the rate change in the
corresponding control volume, known as Reynolds’ transport theorem
dE
dt
system
¼
@
@t
Z
cv
eqdV þ
Z
cs
eq ~ V Á d ~ A
The application of Reynolds’ transport theorem to the LHS of the equation leads
to
@
@t
Z
cv
eqdV þ
Z
cs
eq ~ V Á ^ n dA ¼ _
Q À _
W
The work term on the RHS is developed into
7.2 Engineering Inference of the Entropy-Energy Principles
169
of energy in its exergetic content, i.e., the consideration of exergetic content of
energy is the only way to think in terms of energy intelligently. Another way to
appreciate usefulness in exergetic thinking is that, via the theory of exergy, a
quantitative linkage can be found (see below) between the Carnot–Kelvin formula
and Gibbs free energy, giving unity to the typical core knowledge of mechanical
engineering and typically what chemists and chemical engineers know. Furthermore, we shall find exergy analysis is particularly effective in application to
component processes (the unit operations level) instead of the whole-systems level,
and therefore it is a powerful tool in identifying the problem. Even though it, in
itself offers no solution, but identification of where a better solution is needed is
paramount.
7.2.2 Energy Equation for Open Systems
So far, our discourse has been focused on closed systems since the first law and the
second law are introduced naturally based on the consideration of closed systems.
This focus will continue in Chaps. 8 and 9. But, beginning with this chapter and in
Chap. 10, engineering application, i.e., engineering thermodynamics, will be the
main goal of our discourse. In the realm of engineering application, consideration
must be made to open systems, as many devices are open systems.
Beginning with the first law, Eq. (23), which is rewritten as
dE
dt
¼ _
Q À _
W
ð23BÞ
the first law equation is shown in Chap. 10 to be developed into an equation applied
to a control volume, cv, defining a device. Key assumptions and steps there (see
Chap. 10 for details) are reproduced here.
The system rate equation is related to expressions of the rate change in the
corresponding control volume, known as Reynolds’ transport theorem
dE
dt
system
¼
@
@t
Z
cv
eqdV þ
Z
cs
eq ~ V Á d ~ A
The application of Reynolds’ transport theorem to the LHS of the equation leads
to
@
@t
Z
cv
eqdV þ
Z
cs
eq ~ V Á ^ n dA ¼ _
Q À _
W
The work term on the RHS is developed into
7.2 Engineering Inference of the Entropy-Energy Principles
169