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Heat - Insulation - Conduction - Buildings.
Trapped air can be used in various ways to insulate buildings.
Examples are loft insulation, water tank and pipe insulation, double glazing and
Cavity Wall Insulation.
Many
houses are built with "cavity
walls" consisting of two rows
of bricks.
There is an outside wall and an
inside wall with an air
gap between them.
The air can transfer heat across the gap
by convection.
Cavity wall
insulation involves filling the gap with a polymer foam.
The foam is a type of plastic material which has air trapped inside
it.
The foam replaces the air in the gap
between the bricks.
No heat can now be
transferred by convection
because the air has been replaced by
foam.
Conduction is
very poor
because
both the polymer and the trapped air are
good insulators.
The room in the house stays warmer
for longer (see costs).
Other types of polymer containing trapped air are
bubble-wrap and polystyrene foam.
They are both used for packaging
because they have a low density.
Polystyrene foam is also used for
disposable cups in drinks machines.
The outside of the cup is cool enough to
pick up
although the inside may contain
hot tea
or coffee.
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Copyright © 2008 Dr. Colin France. All Rights Reserved.