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5A1. Advantages of Freon 12. Freon 12 is,
directly the result of a search for the perfect
refrigerant, and it more nearly approaches
that ideal than, any other so far discovered.
The chemical name of Freon 12 is dichlorodifluoromethane. Its chemical symbol is
CC12F2, which means that it contains one part
carbon, two parts chlorine, and two parts
fluorine. In manufacturing Freon 12, fluorine
is substituted for part of the chlorine in carbon tetrachloride, and the result is Freon 12,
with byproducts. This substitution has the
remarkable effect of lowering the boiling
point by 120 degrees, At atmospheric pressure, Freon 12 boils at -21.66 degrees F and freezes
at -311 degrees F. Its latent heat of vaporization at
atmospheric pressure is about 72 Btu per
pound.
Freon 12 has so many advantages that it is
used almost universally on ships today. Its
advantages are as follows:
1. It is a safe refrigerant.
2. It is nonflammable:
3. It is nonexplosive.
4. It is noncorrosive.
5. Its vapor is nontoxic in quantities up to
20 percent by volume.
6. It will not harm foods, fabrics, furs, and
so forth.
7. It is odorless in concentrations of 20 percent or less by volume. In high concentrations
if has a slight odor of carbon tetrachloride,
of which it is a derivative.
8. It is tasteless.
Additional advantages for operation:
9. It has a low boiling point, -21.66 degrees F atmospheric pressure.
10. It acts rapidly in freezing other substances; its latent heat at 5 degrees F is 69.47 Btu, or
much lower than that of other refrigerants.
11. At the high-pressure point of its refrigeration cycle, it operates at comparatively
low pressure; hence, the equipment does not
require heavy mechanical construction.
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12. At the low-pressure point of its refrigeration cycle, it operates at pressures only
slightly above atmospheric pressure, thus reducing the possibility of air entering the system in the event of leakage.
5A2. Disadvantages of Freon 12. Freon 12
has a few disadvantages, but they are far outweighed by its advantages. The disadvantages
are:
1. While Freon 12 is nonflammable, it de
composes in contact with an open flame at
high temperature (1000 degrees F.), giving rise to
phosgene, a highly toxic gas, and other decomposition products.
2. It is an excellent loosener of scale and
dirt that may be left in or may get into the
system. Such material is carried around in the
system and is finally deposited in the strainers. However, some damage may also result
during its journey. In installation or repair,
great care should be taken to prevent the
entry of any foreign matter into the system.
3. It does not mix with water. One important reason why air must be kept out of
the system is that air almost always contains
some water vapor. This water vapor tends to
condense and freeze, thus interfering with
correct operation, and damaging various
valves and other parts of the system,
4. It is absorbed by lubricating oil.
5. SPECIAL NOTE. Liquid Freon 12 must
not be spilled on the skin, and extreme care
must be taken to prevent even tiny drops from
getting into the eyes. The extreme cold produced by Freon 12, nearly 22 degrees below
zero Fahrenheit, is such that even a tiny drop
may cause the moisture in the tissue of the
eyeball near it to freeze, and possibly result
in serious injury to the eye. Moreover, because of the readiness with which lubricating
oil absorbs Freon 12, there is always some
Freon 12 in the oil of refrigerating and air
conditioning systems. It is advisable not to
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