Английский язык. Арланова Т.Л - 33 стр.

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33
Fridge
Refrigeration preserves food by lowering its temperature. It slows down
the growth and reproduction of micro-organisms such as bacteria and the
action of enzymes which cause food to rot.
Refrigeration is based on three principles. Firstly, if a liquid is heated, it
changes to a gas or vapour. When this gas is cooled, it changes back into a
liquid. Secondly, if a gas is allowed to expand, it cools down. If a gas is
compressed, it heats up. Thirdly, lowering the pressure around a liquid helps
it to boil.
To keep the refrigerator at a constant low temperature, heat must be
transferred from the inside of the cabinet to the outside. A refrigerant is used
to do this. It is circulated around the fridge, where it undergoes changes in
pressure and temperature and changes from a liquid to a gas and back
again.
One common refrigerant is a compound of carbon, chlorine, and fluorine
known as R12. This has a very low boiling point: -29°C. At normal room
temperature (about 20°C) the liquid quickly turns into gas. However, newer
refrigerants which are less harmful to the environment, such as KLEA 134a,
are gradually replacing R12.
The refrigeration process begins in the compressor. This compresses
the gas so that it heats up. It then pumps the gas into a condenser, a long
tube in the shape of a zigzag. As the warm gas passes through the
condenser, it heats the surroundings and cools down. By the time it leaves
the condenser, it has condensed back into a liquid.
Liquid leaving the condenser has to flow down a very narrow tube (a
capillary tube). This prevents liquid from leaving the condenser too quickly,
and keeps it at a high pressure.
As the liquid passes from the narrow capillary tube to the larger tubes of
the evaporator, the pressure quickly drops. The liquid turns to vapour, which
expand sand cools. The cold vapour absorbs heat from the fridge. It is then
sucked back into the compressor and the process begins again.
The compressor is switched on and off by a thermostat, a device that
regulates temperature, so that the food is not over-frozen.
Source: 'Inside out: Fridge', Education Guardian
Exercise 3. Language study Principles and laws
Study these extracts from the text above. What kind of statements are they?
1 If a liquid is heated, it changes to a gas or vapour.
2 If a gas is allowed to expand, it cools down.
3 If a gas is compressed, it heats up. Each consists of an action followed
by a result. For example:
Action Result
a liquid is heated it changes to a gas or vapour

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