Environmental Engineering Reference
In-Depth Information
Figure 2.6
Energy transfers and transformations.
ENERGY TRANSFORMATIONS
During these transfers of energy it is clear that the nature of the energy often changes,
although the total quantity of energy involved remains constant. Radiant energy heats the
objects it meets; it is converted from radiant energy to heat energy. Kinetic energy may
similarly be converted to heat energy; the friction of a moving body against another
liberates heat, as we can demonstrate by filing or sawing a piece of wood or metal.
Under natural conditions the range of probable transformations is fairly limited. That
is, the various forms of energy are normally able to be converted to all other forms, but
follow relatively well defined pathways (Figure 2.6) towards the lowest level of energy -
that of heat.
GENERAL PATTERNS AND PRINCIPLES OF
ELECTROMAGNETIC RADIATION
Solar energy is transmitted to Earth in the form of radiant energy. How does this energy
reach us? Why do we receive the amount we do? Why does the energy have the particular
properties it has? To answer these questions we need to examine some of the principles
of radiation.
Radiant energy consists of electromagnetic waves of varying length. Any object
whose temperature is above
absolute zero
(0 K or −273° C) emits radiant energy. The
intensity and the character of this radiation depend upon the temperature of the emitting
object. As the temperature rises, the radiant energy increases in intensity, but
