AUXILIARY MACHINERY AND EQUIPMENT
Ships depend on the reliability of auxiliary systems.
Proper maintenance and operation of auxiliary systems
will enhance the performance of main propulsion
machinery. As a Fireman, you will gain a thorough
knowledge of main propulsion auxiliary machinery and
systems. In this chapter, we will discuss the operation
of refrigeration and air-conditioning equipment, air
compressors, dehydrators, distilling plants, and
purifiers. Other auxiliary machinery includes the
steering gear, the anchor windlass and capstan, cranes,
elevators, winches, and galley and laundry equipment.
Most Navy refrigeration systems use R-12 as a
refrigerant: Chemically, R-12 dichlorodifluoro-
methane (CC 1425F425). R-12 has such a low boiling
point that it cannot exist as a liquid unless it is confined
in a container under pressure. The cycle of operation and
the main components of R- 12 systems are basically the
same as those in other refrigeration and air-conditioning
FUNDAMENTALS OF REFRIGERATION
Refrigeration is a general term. It describes the
process of removing heat from spaces, objects, or
materials and maintaining them at a temperature below
that of the surrounding atmosphere. To produce a
refrigeration effect, the material to be cooled needs only
to be exposed to a colder object or environment. The
heat will flow in its NATURAL direction-that is, from
the warmer material to the colder material.
Refrigeration, then, usually means an artificial way of
lowering the temperature. Mechanical refrigeration is a
mechanical system or apparatus that transfers heat from
one substance to another.
It is easy to understand refrigeration if you know the
relationships among temperature, pressure, and volume,
and how pressure affects liquids and gases. Refer back
to chapter 2 for a review.
The unit of measure for the amount of heat removed
is known as the refrigeration ton. The capacity of a
refrigeration unit is usually stated in refrigeration tons.
The refrigeration ton is based on the cooling effect of 1
ton (2,000 pounds) of ice at 32°F melting in 24 hours.
The latent heat of fusion of ice (or water) is 144 Btus.
Therefore, the number of Btus required to melt 1 ton of
ice is 144 x 2,000= 288,000. The standard refrigeration
ton is defined as the transfer of 288,000 Btus in 24 hours.
On an hourly basis, the refrigeration ton is 12,000 Btus
per hour (288,000 divided by 24).
The refrigeration ton is the standard unit of measure
used to designate the heat-removal capacity of a
refrigeration unit. It is not a measure of the ice-making
capacity of a machine, since the amount of ice that can
be made depends on the initial temperature of the water
and other factors.
Various types of refrigerating systems are used for
naval shipboard refrigeration and air conditioning. The
one usually used for refrigeration purposes is the vapor
compression cycle with reciprocating compressors.
Figure 10-1 shows a general idea of this type of
refrigeration cycle. As you study this system, try to
understand what happens to the refrigerant as it passes
through each part of the cycle. In particular, you need to
understand (1) why the refrigerant changes from liquid
to vapor, (2) why it changes from vapor to liquid, and
(3) what happens in terms of heat because of these
changes of state. In this section, the refrigerant is traced
through its entire cycle, beginning with the thermostatic
expansion valve (TXV).
Liquid refrigerant enters the TXV that separates the
high side of the system and the low side of the system.
This valve regulates the amount of refrigerant that enters
the cooling coil. Because of the pressure differential as
the refrigerant passes through the TXV, some of the
refrigerant flashes to a vapor.
From the TXV, the refrigerant passes into the
cooling coil (or evaporator). The boiling point of the
refrigerant under the low pressure in the evaporator is
about 20°F lower than the temperature of the space in
which the cooling coil is installed. As the liquid boils