2. Introduction
A refrigerator (colloquially fridge) is a popular household appliance that
consists of a thermally insulated compartment and a heat pump (mechanical,
electronic or chemical) that transfers heat from the inside of the fridge to its
external environment so that the inside of the fridge is cooled to a
temperature below the ambient temperature of the room.
Refrigeration is an essential food storage technique in developed countries.
The lower temperature lowers the reproduction rate of bacteria, so the
refrigerator reduces the rate of spoilage.
3. Cont.…
A refrigerator maintains a temperature a
few degrees above the freezing point of
water. Optimum temperature range for
perishable food storage is 3 to 5 °C (37 to
41 °F).
A similar device that maintains a
temperature below the freezing point of
water is called a freezer.
The refrigerator replaced the icebox, which
had been a common household appliance
for almost a century and a half. For this
reason, a refrigerator is sometimes
referred to as an icebox in American
usage.
4. History
In 1834, the first working
vapor-compression
refrigeration system was
built. The first commercial
ice-making machine was
invented in 1854. In 1913,
refrigerators for home use
were invented. In 1923
Frigidaire introduced the first
self-contained unit.
5. Components
It has 4 main components:
Compressor – Pressure producer by compressing gas
Condenser
Evaporator – Heat exchanger
Throttling device – obstructs the flow of liquid
6. Basic principal of refrigeration
The basic principle of refrigeration is simple. You
simply pass a colder liquid continuously around
the object that is to be cooled. This will take heat
from the object. In the example shown, a cold
liquid is passed over an apple, which is to be
cooled. Due to the temperature difference, the
apple loses heat to the refrigerant liquid. The
refrigerant in turn is heated due to heat
absorption from the apple. t is clear that, if we
can produce cold liquid refrigerant continuously,
we can achieve continuous refrigeration. This
simple fact forms the core of the refrigeration
technology
7.
8. Refrigeration cycle
The refrigerant comes into the compressor as a low-pressure gas, it is
compressed and then moves out of the compressor as a high-pressure gas.
The gas then flows to the condenser. Here the gas condenses to a liquid, and
gives off its heat to the outside air.
The liquid then moves to the expansion valve under high pressure. This valve
restricts the flow of the fluid, and lowers its pressure as it leaves the expansion
valve.
The low-pressure liquid then moves to the evaporator, where heat from the
inside air is absorbed and changes it from a liquid to a gas.
As a hot low-pressure gas, the refrigerant moves to the compressor where the
entire cycle is repeated.
9. Refrigerant
Modern refrigerators usually use a refrigerant called HFC-134a (1,1,1,2-
Tetrafluoroethane), which does not deplete the ozone layer, instead of
Freon. A R-134a is now becoming very uncommon in Europe. Newer
refrigerants are being used instead. The main refrigerant now used is R-
600a, or isobutane.
10. Leakage hazard
A gas leak in a refrigerator, although not likely to occur, can decrease the
ability of your refrigerator to do its job correctly.
Although it's not generally believed that such a leak can be hazardous to
your health, the short-term discomfort caused by breathing Freon -- the
gas used in older refrigerators -- can be problematic.
11. Uses of refrigeration
Separation of air into its constituents by fractional distillation. Air is
liquefied at -1910C. Liquefaction temperature of Nitrogen is -1860C and
that of oxygen is -1960C.
Separation of gases in the petroleum industry (Refinery). Lowest
temperature needed is -1600C and the cooling capacity needed are 10000
tons of refrigeration.
Synthetic ammonia plants condense ammonia gas with temperatures
between -200C to +100C before storage or before shipment.
Preservation of food items
Ice manufacturing
