02-01-2013, 12:42 PM
HEAT PIPE TECHNOLOGY
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INTRODUCTION
A heat pipe is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces.
At the hot interface within a heat pipe,at a very low pressure,
a liquid in contact with a thermally conductive solid surface.
The vapour condenses back into a liquid at the cold interface.
The liquid then returns to the hot interface through either capillary action or gravity action where it evaporates once more and repeats the cycle.
In addition, the internal pressure of the heat pipe can be set or adjusted to facilitate the phase change depending on the demands of the working conditions of the thermally managed system.
Components of a Heat Pipe
Configuration of Heat Pipe
Basic Element of the Heat Pipe– Container (closed and vacuum)– Working fluid– Wick (capillary construction)
Container
Metal Tubing, usually copper or aluminum.
Provides a medium with high thermal conductivity.
Shape of tubing can be bent or flattened.
Working Fluid
Pure liquids such as helium, water and liquid silver
Impure solutions cause deposits on the interior of the heat pipe reducing its overall performance.
The type of liquid depends on the temperature range of the application.
Heat Transfer within
a Heat Pipe
Principle of Operation
A heat pipe is a hermetically sealed evacuated tube
It contains a mesh or sintered powder wick a working fluid in both the liquid and vapor phase.
When one end of the tube is heated the liquid turns to vapor absorbing the latent heat of vaporization.
The hot vapor flows to the colder end of the tube where it condenses and gives out the latent heat.
The re-condensed liquid then flows back through the wick to the hot end of the tube.
Since the latent heat of evaporation is usually very large, considerable quantities of heat can be transported with a very small temperature difference from one end to the other.