Composite systems Composite systems are one variety of nonequilibrium
systems that are time independent. A composite system maintains a time-independent disequilibrium existence by its internal constraints. Examples of internal
constraints are “semi-permeable walls” (introduced by van’t Hoff), “impermeable
diathermic walls”, “adiabatic partitions”, “restricted adiabatic partitions” (which
allow transmission of mechanical energy), “chemical reaction barriers”. A composite system is made of several simple subsystems, each of which is defined by the
corresponding internal constraints. Within each simple subsystem, which is either
defined by a physical wall, a movable partition, or by a non-spatially identifiable
chemical barrier, a state of “meta-stable” equilibrium prevails.
Once a constraint is removed, the composite system will undergo change toward
a meta-stable equilibrium that is defined by the remaining constraints; if all the
constraints are removed the resulting change to the system will eventually bring the
system into its internal stable equilibrium state. The determination of the internal
equilibrium state is considered by Callen to be “the core of thermodynamic theory”:
The single, all-encompassing problem of thermodynamics is the determination of the
equilibrium state that eventually results after the removal of internal constraints in a closed,
composite system. [4]
There is merit in the identification of thermodynamics as the science of tendency
toward equilibrium: the clear focus resulted in treatment as one reader put it, “The
best treatment of thermodynamics I have seen.” But, with this identification, Callen
represents the revised view of physicists with regarding to “what thermodynamics
is” by leaving out the engineering heritage of thermodynamics, i.e., engineering
thermodynamics, which originated with studying the relation between heat and
mechanical work. Instead, Callen focuses on the determination of equilibrium state
in the narrow sense of equilibrium thermodynamics (exception is found in Callen’s
Chap. 4, in which obligatory treatment of maximum useful work is given; the case
can be made, however, that Callen’s treatment in [4] represents a paragon of
equilibrium thermodynamics, not engineering thermodynamics).
1.3.1 Nonequilibrium and Irreversibility
Whereas the concept of equilibrium is fundamental to the edifice of thermodynamic
theory, the theory derives its significance from its applications to systems at
equilibrium or near equilibrium as well as to systems far from equilibrium [5] or at
nonequilibrium states. In the former cases, thermodynamic systems of interest are
material objects that EITHER move toward equilibrium states as the natural end states
(which are Callen’s problem) OR are prevented from reaching equilibrium states due
to externally imposed boundary conditions.
The more important applications are the latter cases: applications to systems at
nonequilibrium states (nonequilibrium thermodynamics, NET). As will be
8
1 Introduction: Temperature and Some Comment on Work
systems that are time independent. A composite system maintains a time-independent disequilibrium existence by its internal constraints. Examples of internal
constraints are “semi-permeable walls” (introduced by van’t Hoff), “impermeable
diathermic walls”, “adiabatic partitions”, “restricted adiabatic partitions” (which
allow transmission of mechanical energy), “chemical reaction barriers”. A composite system is made of several simple subsystems, each of which is defined by the
corresponding internal constraints. Within each simple subsystem, which is either
defined by a physical wall, a movable partition, or by a non-spatially identifiable
chemical barrier, a state of “meta-stable” equilibrium prevails.
Once a constraint is removed, the composite system will undergo change toward
a meta-stable equilibrium that is defined by the remaining constraints; if all the
constraints are removed the resulting change to the system will eventually bring the
system into its internal stable equilibrium state. The determination of the internal
equilibrium state is considered by Callen to be “the core of thermodynamic theory”:
The single, all-encompassing problem of thermodynamics is the determination of the
equilibrium state that eventually results after the removal of internal constraints in a closed,
composite system. [4]
There is merit in the identification of thermodynamics as the science of tendency
toward equilibrium: the clear focus resulted in treatment as one reader put it, “The
best treatment of thermodynamics I have seen.” But, with this identification, Callen
represents the revised view of physicists with regarding to “what thermodynamics
is” by leaving out the engineering heritage of thermodynamics, i.e., engineering
thermodynamics, which originated with studying the relation between heat and
mechanical work. Instead, Callen focuses on the determination of equilibrium state
in the narrow sense of equilibrium thermodynamics (exception is found in Callen’s
Chap. 4, in which obligatory treatment of maximum useful work is given; the case
can be made, however, that Callen’s treatment in [4] represents a paragon of
equilibrium thermodynamics, not engineering thermodynamics).
1.3.1 Nonequilibrium and Irreversibility
Whereas the concept of equilibrium is fundamental to the edifice of thermodynamic
theory, the theory derives its significance from its applications to systems at
equilibrium or near equilibrium as well as to systems far from equilibrium [5] or at
nonequilibrium states. In the former cases, thermodynamic systems of interest are
material objects that EITHER move toward equilibrium states as the natural end states
(which are Callen’s problem) OR are prevented from reaching equilibrium states due
to externally imposed boundary conditions.
The more important applications are the latter cases: applications to systems at
nonequilibrium states (nonequilibrium thermodynamics, NET). As will be
8
1 Introduction: Temperature and Some Comment on Work