Learning Objective: Describe the stages of heat theory and the principles involved
in heat transfer, and recognize various components of refrigeration systems and
their application. Recognize the characteristics and procedures required to service
and troubleshoot rcfri gerat ion systems.
Modern refrigeration has many applications, such
as preserving medicine, blood, and the most important
application, the preservation of food. Most foods kept
at room temperature spoil rapidly. This is due to the
rapid growth of bacteria. Refrigeration preserves food
by keeping it cold, which greatly slows down the
growth of bacteria. In days past, blocks of ice were
used in iceboxes to refrigerate food and other items.
These iceboxes were small and not very practical.
Today, mechanical refrigeration systems make
transportation, storage, and use of refrigerated goods
easy and practical.
The installation, operation, adjustment, and repair
of refrigeration equipment are the primary
responsibility of the Utilitiesman rating. To perform
these duties required of a refrigeration mechanic, you
need to understand the principles and theory of
refrigeration and recognize system components and
understand the way they work within the system.
Methods of installing, maintaining, and repairing
refrigeration equipment and maintaining, servicing,
and repairing domestic refrigerators and freezers are
also covered in this chapter.
HEAT AND REFRIGERATION
Learning Objective: Explain the basics of heat theory
and the basic principles of refrigeration.
REFRIGERATION is the process of removing
heat from an area or a substance and is usually done by
an artificial means of lowering the temperature, such
as the use of ice or mechanical refrigeration.
MECHANICAL REFRIGERATION is defined as a
mechanical system or apparatus so designed and
constructed that, through its function, heat is
transferred from one substance to another. Since
refrigeration deals entirely with the removal or transfer
of heat, some knowledge of the nature and effects of
heat is necessary for a clear understanding of the
NATURE OF HEAT
Heat is a form of energy contained to some extent
in every substance on earth. All known elements are
made up of very small particles, known as atoms,
which, when joined together, form molecules. These
molecules are particular to the form they represent.
For example, carbon and hydrogen in certain
combinations form sugar and in others form alcohol.
Molecules are in a constant state of motion. Heat is
a form of molecular energy that results from the motion
of these molecules. The temperature of the molecules
dictates to a degree the molecular activity within a
substance. For this reason, substances exist in three
different states or formssolid, liquid, and gas.
Water, for example, may exist in any one of these
states. As ice, it is a solid; as water, it is a liquid; and as
steam, it is a gas (vapor).
When heat is added to a substance, the rate of
molecular motion increases, causing the substance to
change from a solid to a liquid, and then to a gas
(vapor). For example, in a cube of ice, molecular
motion is slow, but as heat is added, molecular activity
increases, changing the solid "ice" to a liquid "water"
(fig. 6-1). Further application of heat forces the
molecules to greater separation and speeds up their
motion so that the water changes to steam. The steam
formed no longer has a definite volume, such as a solid
or liquid has, but expands and fills whatever space is
provided for it.
Heat cannot be destroyed or lost. However, it can
be transferred from one body or substance to another or
to another form of energy. Since heat is not in itself a
substance, it can best be considered in relation to its