REFRIGERATION
Basic refrigeration
The job of a refrigeration plant is to cool articles
or substances down to, and maintain them at a
temperature lower than the ambient temperature.
Refrigeration can be defined as a process
that removes heat.
The oldest and most well-known among refrigerants
are ice, water, and air. In the beginning, the
sole purpose was to conserve food. The Chinese
were the first to find out that ice increased the life
and improved the taste of drinks and for centuries
Eskimos have conserved food by freezing it.
1. Introduction
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At the beginning of the last century, terms like
bacteria, yeast, mould, enzymes etc. were known.
It had been discovered that the growth of microorganisms
is temperature-dependent, that
growth declines as temperature falls, and that
growth becomes very slow at temperatures below
+10 °C.
As a consequence of this knowledge, it was now
possible to use refrigeration to conserve foodstuffs
and natural ice came into use for this purpose.
The first mechanical refrigerators for the production
of ice appeared around the year 1860. In
1880 the first ammonia compressors and insulated
cold stores were put into use in the USA.
Electricity began to play a part at the beginning
of this century and mechanical refrigeration
plants became common in some fields: e.g. breweries,
slaughter-houses, fishery, ice production,
for example.
After the Second World War the development of
small hermetic refrigeration compressors evolved
and refrigerators and freezers began to take their
place in the home. Today, these appliances are regarded
as normal household necessities.
There are countless applications for refrigeration
plants now. Examples are:
Foodstuff conservation
Process refrigeration
Air conditioning plants
Drying plants
Fresh water installations
Refrigerated containers
Heat pumps
Ice production
Freeze-drying
Transport refrigeration
In fact, it is difficult to imagine life without air
conditioning, refrigeration and freezing - their
impact on our existence is much greater than mos people imagine

Components of Refrigeration Systems

Refrigeration compressor

The refrigeration process is, as implied, a closed
circuit. The refrigerant is not allowed to expand to
free air.
When the refrigerant coming from the evaporator
is fed to a tank the pressure in the tank will
rise until it equals the pressure in the evaporator.
Therefore, refrigerant flow will cease and the temperature
in both tank and evaporator will gradually
rise to ambient.
To maintain a lower pressure, and, with it a lower
temperature it is necessary to remove vapour.
This is done by the compressor, which sucks vapour
away from the evaporator. In simple terms,
the compressor can be compared to a pump that
conveys vapour in the refrigeration circuit.
In a closed circuit a condition of equilibrium will
always prevail. To illustrate this, if the compressor
sucks vapour away faster than it can be formed in
the evaporator the pressure will fall and with it
the temperature in the evaporator. Conversely, if
the load on the evaporator rises and the refrigerant
evaporates quicker, the pressure and with it
the temperature in the evaporator will rise.