Heeat pipes 热管

　　Operation: Heeat pipes are closed evaporator-condenser system consisting of a sealed, hollow tube whose inside walls are lined with a capillary structure of wick. A thermodynamic working fluid having a substantial vapor pressure at the desired operating temperature saturates the pores of wick. When heat is applied to the heat pipe, it's fluid is heated and evaporates. As the evaporating fluid fills the hollow center of the wick, it diffuses throughout the heat pipe.
　　Condensation of the vapor occurs wherever the temperature is even slightly bellow that of the evaporation area. As it condenses, the vapor gives up the heat it acquired when it evaporated. This tends to produce a constant temperature and a highly effective thermal conductance. When a heat sink is attached to a portion of the heat pipe, condensate takes place at this point of heat loss
and a vapor flow pattern is established. The return of the condensate to the evaporator, or heat source is accomplished by means of capillary action within the wick and the operating cycle is complete.
　　This system, proven in aerospace applications, transmits thermal energy at rates hundreds of times greater than the most efficient solid conductor and at a far superior energy-to-weight ratio.
　　Advantages: The heat pipe has several properties of value to the electronics industry. First and most obvious is it's high thermal conductance. The seconds, is it's ability to concentrate or disperse thermal power density. This property is most useful in matching heat sources and heat sinks of widely differing thermal characteristics. Third property relates to heat pipe's ability to separate the heat source and heat sink. For example, a power device may be located in a n area where insufficient space is available to locate a standard type heat sink capable of dispersing the heat to an acceptable level. It may then be possible to use a heat pipe to transfer heat from it's source to remotely located heat sink.