However this instability has not been studied until recently.
Such important parameters as oscillation threshold, heat transfer coefficient, and maximum heat load cannot be predicted from calculations.
For comparison, advanced heat pipes used for spatial applications have heat transfer capacity (measured in W∙m) order of value smaller.
The heat transfer capacity of the conventional heat pipes used for cooling of microelectronic devices like laptop computers is 2 to 3 orders of value smaller than that of PHPs.
The other end (called condenser section) is connected to the cold point where the heat can be dissipated.
A portion of the tube between evaporator and condenser is called adiabatic section.A heat pipe is a container tube filled with the working fluid.One end of this tube (called evaporator section) is brought in thermal contact with a hot point to be cooled.These features make PHP extremely promising for the thermal management of the next generation of electronic and other systems.However, the functioning of PHPs is not completely understood.When the temperature difference between evaporator and condenser exceeds a certain threshold, the gas bubbles and liquid plugs begin to oscillate spontaneously back and forth.The amplitude of oscillations is quite strong and the liquid plugs penetrate into both condenser and evaporator.PHP is a capillary tube (with no wick structure) bent into many turns and partially filled with a working fluid.Because the tube is thin, the liquid plugs and vapor bubbles are formed inside it. This requires replacing of metals by lighter synthetic materials (composites, ceramics, etc.), which, however, are poor heat conductors and thus require special thermal management solutions for their cooling capability to handle heat loads up to several k W.On the other hand, with the increase of power levels related to the miniaturization of electronics progressing towards multi chip modules, conventional cooling technologies and thermal management are facing growing challenges including the cooling heat fluxes of 100 W/cm, long term reliability, and very low costs for consumer market products, among others.