Some of the shortcomings associated with conventional
solar collectors include extra expense of the forced
circulation system due to the pump and its extracted
power,of the water on cold nights, pipe corrosion due to the use
of water and the limited quantity of heat transferred by
the heat transfer fluid. Heat pipes offer a promising solution
to these problems. Heat pipes working under gravity
with the condenser above the evaporator do not
require external power or capillary action in order to return
the heat transfer fluid to the evaporator. This type
of heat pipe is known as the gravity assisted heat pipe,
closed two-phase thermosyphon or wickless gravity assisted
heat pipe.