New trends in physics teaching, v.4; The ... - unesdoc - Unesco

Energy degradation
Therefore ‘the general struggle for life of all creatures is not a struggle for raw material. . .
nor for energy, which is, unfortunately, unchangeable, contained in every body, but a struggle
for entropy [we would say: for energy upgrading] which becomes available by the transfer of
energy from the hot Sun to the cold Earth’ (Boltzmann, [ 6, p.401).
On the value of different energy forms
For understanding and estimating most of the energy problems in the world today the scheme
of energy degradation described above may be simplified by abstaining from the processes and
concentrating attention on the different forms of energy involved. By assigning a certain value
to each form of energy, we can at least give a rough estimate of the events in the spirit of our
degradation concept.
For instance, electrical energy may be regarded as being more valuable than heat. We can see
that this is so by noting that, while it is not possible to drive (in any simple way) a television set
or a vacuum cleaner with heat, heat at the temperature we need may readily be produced by
electrical energy. Electrical energy is universally applicable. In principle, it may be used to
reverse other processes (although the opposite does not hold). A definite quantity of electrical
energy may be used to drive in reverse another process which involves the same quantity of
energy in a different form. This is also true of mechanical energy; so we may assign the same
high value or grade to both electrical and mechanical energy.
Generally speaking, the following sequence provides a hierarchical scheme which may be
used in the qualitative examination of energetic events:
High grade or value
Mechanical, electrical energy
L 4
Chemical energy
4
Thermal energy (0 )
3-
Thermal energy (0,)
Low grade or value (5)
This assumes that mechanical and electrical energies are the most valuable whilst thermal energy
is lessvaluable. More precisely, the value of the thermal energy (heat) depends on the temperature
(e) at which it appears or is transferred; the higher the temperature, the more valuable is the
energy. This will be considered in more detail below. Here it may suffice to remark that a body at
a high temperature can be used to heat a cold body, (i.e. can reverse its cooling down) while the
opposite is impossible. In practice, the thermal energy of the (coldest) surroundings has no value,
because nothing can be driven in reverse by this energy.
Chemical energy holds a middle place in the value sequence for, in chemical processes, since a
part of the energy is emitted as heat at a finite temperature, the chemical energy is not as valuable
as electrical and mechanical energies. But, in the domain of normal temperatures, chemical
energy is generally more valuable than thermal energy.
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