one example where the second exergy definition does not apply and, strictly
speaking, the concept of exergy becomes problematic.
If we overlook the case of the exergy of cold, the above discussion shows that
exergy analysis is consistent with the Gibbs function and the Gibbs free energy as
well as with the Carnot–Kelvin formula as special cases, respectively. This
demonstration encourages the notion that exergy analysis, though not perfect
because of definitional contradiction (thus, it is not the final formulation of our
analysis), is nonetheless a powerful tool for engineering practice.
7.6 Energy: Exergetic Content of Energy
and the Definition of Energy
As long as both pure exergy energies and material exergy are core parts of the
theory of exergy, the theory of exergy rests on both the first definition and the
second definition with the aforementioned contradiction between them. The only
escape out of the dilemma is for the first definition to accept the restriction implied
in the second definition, energy ¼ exergy þ anergy. That is, the “energetic” interpretation of thermodynamics in accordance with MTH. This interpretation restriction is, in fact, the widely held understanding of thermodynamics since Kelvin. In
this interpretation, energy is divided into four kinds inclusively
• Pure exergy energy: electrical energy, kinetic energy, and potential energy
• High exergy energy: high temperature heat, electrochemical systems
• Low exergy energy: low-temperature heat
• Zero exergy energy: heat of a body that is in thermodynamic equilibrium with its
environment.
The common definition of energy, energy is the capacity for doing work, is
clearly applicable only to the pure exergy energies, while applicable poorly to high
exergy energies and inapplicable to low exergy energy and zero exergy energy. In
contrast, relating exergetic content of an energy system to be the capacity for doing
work is applicable to all four cases. I propose the following definition of energy:
Energy is a conserved quantity that can be neither created nor destroyed; an important
characteristic of the quantity is its exergetic content, which is measured in terms of the
system capacity for doing work; although energy of a system and its interacting surroundings cannot be destroyed, the system-surroundings capacity for doing work is being
lost incessantly.
Thermodynamics had begun as an engineering subject of the study of heat and
work (see Fig. 7.1). Joule established the idea that both work and heat are forms of
energy, which is universally conserved. Kelvin introduced the general idea of
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7 Free Energy, Exergy, and Energy …
speaking, the concept of exergy becomes problematic.
If we overlook the case of the exergy of cold, the above discussion shows that
exergy analysis is consistent with the Gibbs function and the Gibbs free energy as
well as with the Carnot–Kelvin formula as special cases, respectively. This
demonstration encourages the notion that exergy analysis, though not perfect
because of definitional contradiction (thus, it is not the final formulation of our
analysis), is nonetheless a powerful tool for engineering practice.
7.6 Energy: Exergetic Content of Energy
and the Definition of Energy
As long as both pure exergy energies and material exergy are core parts of the
theory of exergy, the theory of exergy rests on both the first definition and the
second definition with the aforementioned contradiction between them. The only
escape out of the dilemma is for the first definition to accept the restriction implied
in the second definition, energy ¼ exergy þ anergy. That is, the “energetic” interpretation of thermodynamics in accordance with MTH. This interpretation restriction is, in fact, the widely held understanding of thermodynamics since Kelvin. In
this interpretation, energy is divided into four kinds inclusively
• Pure exergy energy: electrical energy, kinetic energy, and potential energy
• High exergy energy: high temperature heat, electrochemical systems
• Low exergy energy: low-temperature heat
• Zero exergy energy: heat of a body that is in thermodynamic equilibrium with its
environment.
The common definition of energy, energy is the capacity for doing work, is
clearly applicable only to the pure exergy energies, while applicable poorly to high
exergy energies and inapplicable to low exergy energy and zero exergy energy. In
contrast, relating exergetic content of an energy system to be the capacity for doing
work is applicable to all four cases. I propose the following definition of energy:
Energy is a conserved quantity that can be neither created nor destroyed; an important
characteristic of the quantity is its exergetic content, which is measured in terms of the
system capacity for doing work; although energy of a system and its interacting surroundings cannot be destroyed, the system-surroundings capacity for doing work is being
lost incessantly.
Thermodynamics had begun as an engineering subject of the study of heat and
work (see Fig. 7.1). Joule established the idea that both work and heat are forms of
energy, which is universally conserved. Kelvin introduced the general idea of
184
7 Free Energy, Exergy, and Energy …