Abstract :
A heat pipe
is a device that efficiently transports thermal energy from its one point to the
other. It utilizes the latent heat of the vaporized working fluid instead of
the sensible heat. As a result,
the effective thermal conductivity may be several orders of magnitudes higher than
that of the good solid conductors.
A heat pipe
consists of a sealed container, a wick structure, a small amount of working fluid
that is just sufficient to saturate the wick and it is in equilibrium with its
own vapor. The operating pressure inside the heat pipe is the vapor pressure of
its working fluid. The length
of the heat pipe can be divided into three parts viz. evaporator section, adiabatic
section and condenser section. In a standard
heat pipe, the inside of the container is lined with a wicking material. Space for
the vapor travel is provided inside the container.
How a Heat Pipe
Works
A heat pipe
is a closed evaporator-condenser system consisting of a sealed, hollow tube whose
inside walls are lined with a capillary structure or wick. Thermodynamic working
fluid, with substantial vapor pressure at the desired operating temperature,
saturates the pores of the wick in a state of equilibrium between liquid and vapor.
When heat is applied to the heat pipe, the liquid in the wick heats and evaporates.
As the evaporating fluid fills the heat pipe hollow center, it diffuses throughout
its length. Condensation of the vapor occurs wherever the temperature is even
slightly below that of the evaporation area. As it condenses, the vapor gives
up the heat it acquired during evaporation. This effective high thermal conductance
helps maintain near constant temperatures along the entire length of the pipe.
Attaching a
heat sink to a portion of the heat pipe makes condensation take place at this
point of heat transfer and establishes a vapor flow pattern. Capillary action
within the wick returns the condensate to the evaporator (heat source) and completes
the operating cycle. This system, proven in aerospace applications, transmits thermal
energy at rates hundreds of times greater and with a far superior energy-to-weight
ratio than can be gained from the most efficient solid.
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