A heat pipe is a
device used to transfer heat from one
end to the other more
effectively than a
rod of massive
metal.
It works by a liquid
boiling away at the hot end, and
condensating at the cold end. The
condensate is then re-transferred to the hot end by the
means of a
wick, or simply by
gravity if that is possible.
The
phase change from
liquid to
gas takes a lot of
energy and has the additional
benefit that the hot end can't get any hotter than the boiling point of the liquid in question, as long as the heat pipes
specs are not crossed.
The problem with this design is that it has to be matched to the type of heat source by choosing the
appropriate liquid, boiling point and amount of liquid in the device, as it will work effectively only in a
narrow band of temperature/amount of energy.
In low-range temperatures (30° - 80°C),
alcohol under normal or reduced
pressure is often used. In higher ranges, liquid metals are the
medium of choice.