A simple way to address this difference between work and heat is that work
exchange is not associated with entropy flow (see Fig. 4.5), while heat flow is
always associated with entropy flow (see Eq. [62A], and definition of heat below):
explicit considerations of how entropy
2 are involved is the best way to differentiate
energy exchange in the form of work from energy exchange in the form of heat.
The second objection, if valid, is a much more serious objection. As it was noted
in Table 3.1 summarizing the energy conservation principle, it originated from the
conceptual differentiation of caloric into heat exchange and heat energy. By using
the same term, heat, when one speaks of heat exchange and heat energy, one is
guilty of denying the conceptual difference between the two. But, this is simply not
the case.
The conceptual differentiation of caloric, as it was discussed in Chaps. 3 and 4,
did not stop at heat energy. Heat energy, or thermal internal energy, is a special
form of internal energy. The introduction of internal energy by Clausius and energy
(=internal energy + mechanical energy) by Kelvin (see Chap. 4) are, therefore,
additional steps beyond the initial conceptual differentiation phase, #1 in Table 3.1.
The complete conceptual differentiation consists of steps #1, #3, and #5 in Sect. 3.3
together. When one uses heat to mean heat energy, there is no risk in treating heat
as a substance unless one denies the transformation of energy from one form to
another. It is safe to note that the triumph of MTH over the caloric theory is safe
that everyone accepts the existence of energy transformation, even though the
triumph is tainted for a different reason as I shall address that issue in Chap. 8.
This subtle point is critical for sorting out the way how physicists and engineers
use the term “heat” including specific heats, latent heats, waste heat, etc.
Our serious linguistic dilemma resulted from the inability of defining heat on the
one hand, and the drastic step of stripping heat down to its barebone Q on the other
hand. A middle ground can be found between the broadest meaning of heat and the
narrowest interpretation of heat as Q by defining heat as “a process and as a state
function corresponding to natural end states of spontaneous changes”:
Definition of Heat: Heat, as denoted by Q, is energy and entropy in transit; waste heat or
heat in a body (i.e., heat used as short for thermal internal energy) is high-entropy, i.e.,
lowest-grade, form of energy.
This is how we use the term of heat, and there should be no objection to this use:
any remaining objection will be addressed in Chap. 8. How we use the term energy
will be discussed in Chap. 7 when we consider energy together with the concept of
exergy.
2
Take the example of the system of a cooking vessel, which is brought to a very high temperature
in two ways of cooking. Electric resistive coil cooking is an example of heat-exchange process
carrying both energy flow and its associated entropy flow; electric induction cooking is an example
of (electromagnetic field energy) work-exchange process carrying no entropy flow—with heat
generation entropy-production process taking place inside cooking vessel. Entropy gain in the
former case results from entropy in-flow across the boundary of the vessel and in the latter case
from entropy production within the boundary.
106
5 Entropy and the Entropy Principle
exchange is not associated with entropy flow (see Fig. 4.5), while heat flow is
always associated with entropy flow (see Eq. [62A], and definition of heat below):
explicit considerations of how entropy
2 are involved is the best way to differentiate
energy exchange in the form of work from energy exchange in the form of heat.
The second objection, if valid, is a much more serious objection. As it was noted
in Table 3.1 summarizing the energy conservation principle, it originated from the
conceptual differentiation of caloric into heat exchange and heat energy. By using
the same term, heat, when one speaks of heat exchange and heat energy, one is
guilty of denying the conceptual difference between the two. But, this is simply not
the case.
The conceptual differentiation of caloric, as it was discussed in Chaps. 3 and 4,
did not stop at heat energy. Heat energy, or thermal internal energy, is a special
form of internal energy. The introduction of internal energy by Clausius and energy
(=internal energy + mechanical energy) by Kelvin (see Chap. 4) are, therefore,
additional steps beyond the initial conceptual differentiation phase, #1 in Table 3.1.
The complete conceptual differentiation consists of steps #1, #3, and #5 in Sect. 3.3
together. When one uses heat to mean heat energy, there is no risk in treating heat
as a substance unless one denies the transformation of energy from one form to
another. It is safe to note that the triumph of MTH over the caloric theory is safe
that everyone accepts the existence of energy transformation, even though the
triumph is tainted for a different reason as I shall address that issue in Chap. 8.
This subtle point is critical for sorting out the way how physicists and engineers
use the term “heat” including specific heats, latent heats, waste heat, etc.
Our serious linguistic dilemma resulted from the inability of defining heat on the
one hand, and the drastic step of stripping heat down to its barebone Q on the other
hand. A middle ground can be found between the broadest meaning of heat and the
narrowest interpretation of heat as Q by defining heat as “a process and as a state
function corresponding to natural end states of spontaneous changes”:
Definition of Heat: Heat, as denoted by Q, is energy and entropy in transit; waste heat or
heat in a body (i.e., heat used as short for thermal internal energy) is high-entropy, i.e.,
lowest-grade, form of energy.
This is how we use the term of heat, and there should be no objection to this use:
any remaining objection will be addressed in Chap. 8. How we use the term energy
will be discussed in Chap. 7 when we consider energy together with the concept of
exergy.
2
Take the example of the system of a cooking vessel, which is brought to a very high temperature
in two ways of cooking. Electric resistive coil cooking is an example of heat-exchange process
carrying both energy flow and its associated entropy flow; electric induction cooking is an example
of (electromagnetic field energy) work-exchange process carrying no entropy flow—with heat
generation entropy-production process taking place inside cooking vessel. Entropy gain in the
former case results from entropy in-flow across the boundary of the vessel and in the latter case
from entropy production within the boundary.
106
5 Entropy and the Entropy Principle