Recent Technology involves usage of Heat Pipe in Air Heater

A heat pipe is a device with a high thermal conductance. It is based on the large latent heat of vaporization/condensation of working fluid inside the heat pipe. Hence all heat pipes are completely sealed one and the working fluid is the heat transfer element between the to and cold  fluid passing through its ends separated by partition plate. In heat pipe heat is absorbed in the evaporated portion of the heat pipe and of vapourize the internal working fluid. The vapour is transferred to the condenser portion on the other end where the fluid surrenders the heat to the cold surrounding and condenses. This fluid is then returned to the evaporator and the cycle is repeated. Heat pipe contains a working fluid specifically selected for operating temperature range and hence heat pipes are arranged in modules containing different working fluid for the range of temperature.

Types  of  heat pipes differ according to the method used to transport the working fluid.

• Thermo-syphon heat pipe

  The name itself indicates heat pipes uses gravity, buoyancy and vapour pressure forces to transport the phase of the working fluid. It requires the heat source to be below the heat sink that is evaporator must be below the condenser. The vapour generated in the evaporator travels upward because of the buoyancy and expansion forces. In the cons\denser the vapour is condensed to a liquid and turns to the evaporator by gravity. The thermo siphon heat pipe can be made to function efficiently with an orientation of approximately 10 to 90 degree form horizontal.

• Capillary action heat pipe

  The working fluid is transferred through capillary action and it does not require gravity to return the condensate to the evaporate section. This type of heat pipes contain an internal element known as wick, which spans the length of the pipe. The wick may be made of gauze wire mesh or other materials that provide closely spaced longitudinal paths for returning  condensate. The path spacing is chosen based on the working fluid to obtain high capillary forces and there are no orientation restriction for this type of heat pipe.

  There should not be gap between heat source and sink in the heat pipe. If a gap exists then it can be spanned by an adiabatic section of heat pipe. This adiabatic region is created by externally insulating the appropriate section of heat pipe.