2. Air cooling is a method of dissipating heat. It
works by making the object to be cooled have a
larger surface area or have an increased flow of
air over its surface, or both. An example of the
former is to add fins to the surface of the object,
either by making them integral or by attaching
them tightly to the object's surface (to ensure
efficient heat transfer). In the case of the latter it
is done by using a fan blowing air into or onto
the object one wants to cool. In many cases the
addition of fins adds to the total surface area
making a heatsink that makes for greater
efficiency in cooling.
3. In all cases, the air has to be cooler than the
object or surface from which it is expected to
remove heat. This is due to the second law of
thermodynamics, which states that heat will
only move spontaneously from a hot reservoir
(the heat sink) to a cold reservoir (the air).
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4. Air is mainly used for air-cooled internal
combustion engines (ICE), particularly those
powering aircraft, because it is a readily available
fluid and is often at a suitable temperature to be
used efficiently. While many such ICE are called
"liquid cooled" the cooling liquid is usually
cooled by air passing through a radiator or heat
exchanger. Examples of direct air cooling in
modern automobiles are rare. The most common
example is the Flat engine orBoxer engine, once
used extensively by Porsche and still in use on
BMW motorcycles.
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5. A very large number of industrial processes use air as
a cooling medium, either directly or indirectly. Air
conditioning is a very common process in which the
air in a room, or a whole building, is cooled in order
to maintain a comfortable environment for its
occupants. Often the air has been cooled by chilled
water or brine and the heat transferred to that
medium is transported outside the building where,
often, fan-driven water-to-air heat exchanging is
again effected to reject the heat into the atmosphere.
A common sight around, for example, power
station are the large waisted concrete towers that
emit steam more or less constantly. These are, in
part, using air cooling on a grand scale
