Page 38 - Curriculum Visions Dynamic Book

CFCs
Fluorine and chlorine have been widely used to make the coolant in refrigerators. Refrigerants are varieties of substances that include chlorine, fluorine and carbon, called chlorofluorocarbons
or more commonly just CFCs.
The properties of CFCs were found
to be excellent for use in a number of
industries. They are not poisonous, they
do not catch fire, they absorb large amounts
of heat, and they can be made to change from
liquid to gas at temperatures that are just right for use in refrigerators. Because CFCs do not easily react with other chemicals, they also proved to be very good for use in aerosol cans, acting as the gas that expels the liquid from the can in a fine mist.
The first CFCs were made in the 1930s. However, by the 1970s it was becoming clear that CFCs
were not as safe as had once been thought. Their continued and escalating use was destroying the ozone layer high in the atmosphere. As a result, CFCs are being replaced with other refrigerants and gases as fast as is practical.
 The gradual enlargement of
the ozone hole – the region of the upper stratosphere that has been depleted of ozone – is thought
to be largely the result of ozone reacting with the CFC molecules released from the ground. Recent attempts to limit the production of CFCs are designed to prevent more destruction of the ozone, a vital shield against the cancer-producing ultraviolet rays of the Sun.
 CFCs such as Freon-11 (CFCl3) are used as refrigerants.
Fluorine
Carbon
Chlorine
Refrigerant is put through a thin panel in an ice box to give a large surface area.
Heat inside the refrigerator is absorbed by refrigerant in pipes, cooling the interior.
 A diagram of the mechanism of a refrigerator. CFCs are very efficient coolants because of
their high thermal capacity and boiling points. They are also cheap to manufacture. Finding replacement chemicals is proving to be extremely difficult.
Heat is dissipated from refrigerant in the grill at the back.
Pump
38
38