What Is Heat Pipe?

The Origin And Development Of Heat Pipes

Heat pipe technology appeared as early as 1942, when Perkins invented and improved the thermosyphon (a simple gravity heat pipe). After 1942, Gaugler proposed the principle of modern heat pipes, but did not apply them in practice. It was not until 1963 that G.M. Grover again proposed this principle at Los Alamos National Laboratory in the United States. And invented the heat transfer element named "heat pipe".

The heatpipe heatsink is a kind of heat transfer element, which makes full use of the principle of heat conduction and the fast heat transfer properties of the refrigerant. The heat of the heating object is quickly transferred to the heat source through the heat pipe, and its thermal conductivity has far exceeded any known metal. The thermal conductivity. In the past, heat pipe technology has been widely used in aerospace, military industry and other industries, and it has been introduced into the radiator manufacturing industry in recent years.

It is precisely because of the existence of heat pipe technology that people have changed the design thinking of traditional radiators and got rid of the traditional cooling mode that simply relies on large air volume fans for better heat dissipation. Instead, it adopts a new cooling mode that uses a low-speed, low-volume fan and heat pipe technology. The heat pipe cpu cooler brings an opportunity to the silent era of the PC.

The Working Principle Of The Heat Pipe

The heat absorption and heat release of an object are relative. Whenever there is a temperature difference, the phenomenon of heat transfer from a high temperature to a low temperature will inevitably occur. There are three ways of heat transfer: radiation, convection, and conduction, of which heat conduction is the fastest. The heat pipe heat sink is the use of evaporative cooling, which makes the temperature difference between the two ends of the heat pipe large, so that the heat is quickly transferred.

When one end of the heat pipe is heated, the liquid in the capillary wick evaporates and vaporizes. The steam flows to the other end under a slight pressure difference, releasing heat and condensing into a liquid. The liquid then flows back along the porous material to evaporate under the action of capillary force (or gravity). segment. In this way, the heat is transferred from one end to the other.

Basic Characteristics Of Heat Pipe

The heat pipe is a heat transfer component that relies on the phase change of its internal working liquid to realize heat transfer. It has the following basic characteristics:

1) Very high thermal conductivity. The inside of the heat pipe mainly relies on the vapor and liquid phase of the working fluid to transfer heat, and the thermal resistance is very small, so it has a high thermal conductivity.

2) Excellent isothermal properties. The steam in the inner cavity of the heat pipe is in a saturated state. The pressure of the saturated steam is determined by the saturation temperature. The pressure drop of the saturated steam flowing from the evaporation section to the condensation section is very small. According to the Clausuis-Clapeyron equation in thermodynamics, the temperature drop is also very small. Therefore, the heat pipe has excellent isothermal properties.

3) Heat flux variability. The heat pipe can independently change the heating area of the evaporation section or the condensation section, that is, input heat with a smaller heating area, and output heat with a larger cooling area, and vice versa. This can change the heat flux density and solve some heat transfer problems that are difficult to solve by other methods.

4) The reversibility of the direction of heat flow. For a horizontally placed cored heat pipe, since its internal circulation power is capillary force, either end of the heat pipe can be used as an evaporation section, and the other end can be used as a condensing section when the heat is dissipated outside. This feature can be used to flatten the temperature of spacecraft and artificial satellites in space, and can also be used in chemical reactors and other devices that first release heat and then absorb heat.

5) Thermal diode and thermal switch performance. The heat pipe can be made into a thermal diode or a thermal switch. The so-called thermal diode only allows heat to flow in one direction, not the opposite direction; the thermal switch is when the temperature of the heat source is higher than a certain temperature, the heat pipe starts to work, and when the temperature of the heat source is lower than this temperature, the heat pipe No heat is transferred.

6) Constant temperature characteristics (controllable heat pipe). The thermal resistance of each part of the ordinary heat pipe basically does not change with the change of the heating amount, but the variable heat pipe makes the thermal resistance of the condensing section decrease with the increase of the heating amount, and increase with the decrease of the heating amount, so that the heat pipe can be In the case of a large change in the heating capacity, the temperature of the steam changes very little, and the temperature is controlled. This is the constant temperature characteristic of the heat pipe.

7) Environmental adaptability. The shape of the heat pipe can vary with the conditions of the heat source and the cold source.

Factors To Be Considered When Designing Heat Pipes

Heat pipes are often used in current heat dissipation design, including our common notebook computers, mobile phones, etc., all have heat pipes. The following factors need to be considered when designing a heat pipe: thermal load or heat to be transferred; working temperature; pipe material; working fluid; capillary structure; length and diameter of the heat pipe; contact length of the evaporation zone; contact length of the compensation zone; direction; heat pipe bending The impact of peace and so on.

Application Of Heat Pipe

Heat pipe technology was first applied to space vehicles. Because the parts of the spacecraft face and face the sun with a large temperature difference and are easily damaged, heat pipes can be used to achieve thermal equilibrium and solve the problem. It is currently used in satellites, space vehicles, space suits and other aspects of high heat transfer and small temperature difference heat transfer.

With the continuous improvement of the level of science and technology, the field of heat pipe research and application is also expanding, especially the emergence of micro heat pipe technology, making heat pipes used in medical operations, electronic device chips, notebook computer CPU cooling, circuit control board cooling, The application of solar water heaters, solar power plants, and nuclear power projects has been greatly developed. In addition, heat pipes are also used to stabilize the permafrost. Oil pipelines or railways in plateau areas can be used to prevent damage to the frozen soil.