2. Definition
Refrigeration is a process of removing heat from a low-
temperature reservoir and transferring it to a high-
temperature reservoir. The work of heat transfer is
traditionally driven by mechanical means, but can also
be driven by heat, magnetism, electricity, laser, or other
means. Refrigeration has many applications, including,
but not limited to: household refrigerators, industrial
freezers, cryogenics, and air conditioning. Heat pumps
may use the heat output of the refrigeration process,
and also may be designed to be reversible, but are
otherwise similar to air conditioning units. Refrigeration
has had a large impact on industry, lifestyle, agriculture,
and settlement patterns
3. The introduction of refrigerated rail cars
contributed to the westward expansion of the
United States, allowing settlement in areas that
were not on main transport channels such as
rivers, harbors, or valley trails. Settlements
were also developing in infertile parts of the
country, filled with newly discovered natural
resources. These new settlement patterns
sparked the building of large cities which are
able to thrive in areas that were otherwise
thought to be inhospitable, such as Houston,
Texas, and Las Vegas, Nevada.
4. History
Before 1830, few Americans used ice to
refrigerate foods due to a lack of ice-
storehouses and iceboxes. As these two things
became more widely available, individuals
used axes and saws to harvest ice for their
storehouses. This method proved to be
difficult, dangerous, and certainly did not
resemble anything that could be duplicated on
a commercial scale.
5. Refrigerator
If you place your hand behind an operating
refrigerator, you will notice that this area is warmer
than the room temperature. Or you may notice that
the refrigerator blows warm air on your feet as you
stand in front of it. Yet the interior of the freezing
compartment is very cold! The refrigerator is taking
energy from the freezing compartment, making it
colder, and exhausting that heat to the room,
making it warmer.
A refrigerator is a heat engine in which work is done
on a refrigerant substance in order to collect energy
from a cold region and exhaust it in a higher
temperature region, therby further cooling the cold
region.
6. The transfer of heat from a low-temperature medium to a high-
temperature one requires special devices called refrigerators.
Refrigerators, like heat engines, are cyclic devices. The working
fluid used in the refrigeration cycle is called a refrigerant. The
most frequently used refrigeration cycle is the vapor-compression
refrigeration cycle, which involves four main components: a
compressor, a condenser, an expansion valve, and an evaporator,
as shown in Fig. 6–19. The refrigerant enters the compressor as a
vapor and is compressed to the condenser pressure. It leaves the
compressor at a relatively high temperature and cools down and
condenses as it flows through the coils of the condenser by
rejecting heat to the surrounding medium. It then enters a
capillary tube where its pressure and temperature drop drastically
due to the throttling effect. The low-temperature refrigerant then
enters the evaporator, where it evaporates by absorbing heat from
the refrigerated space. The cycle is completed as the refrigerant
leaves the evaporator and reenters the compressor.
7. A refrigerator is shown
schematically in Fig. 6–20. Here QL
is the magnitude of the heat
removed from the refrigerated
space at temperature TL, QH is
the magnitude of the heat rejected
to the warm environment at
temperature TH, and Wnet,in is
the net work input to the
refrigerator. As discussed before,
QL and QH represent magnitudes
and thus are positive quantities.
8. Uses of refrigerator
The numbers used to adjust the
temperature on most home
refrigerators only raise or lower the
temperature. They do not match
specific temperatures. A different
setting may be needed during
warmer months than colder
months to maintain the same
temperature. Using a
refrigerator/freezer thermometer
is the only way to assure your
refrigerator and freezer is at the
correct temperature.
