Now, in the field of technology related to “heat”, the technical term “heat pipe” is being recognized by more and more people.Heat pipe, a highly efficient heat transfer element called superconductor, has aroused great interest for its unique heat transfer characteristics since it came into being.Whether in theory or in application, heat pipe is developing rapidly with the tide of new technological revolution.In the science park where new technologies, new processes and new inventions are springing up like mushrooms after a spring rain, heat pipe, a new branch of science, with its unique vitality, has been deeply rooted and rich in fruits in a very short time.
Heat pipe, according to the more precise definition, called “closed two heat transfer system”, that is, in a closed system, rely on the fluid phase change (liquid phase into vapor phase and vapor phase into liquid phase) to transfer heat device.This Heat transfer principle of Heat pipe was first discovered by an American named R. S. Gaugler in 1944 and patented as “Heat Transter Device”. At that time, it did not receive due attention because it did not show practical significance.Until the early ’60 s, due to the development of the aerospace industry, the requirement for the aerospace craft to provide high efficiency Heat transfer element, prompted the luo, los alamos scientific laboratory gloval (g. m. Grover) on the basis of the independent work in 1964, once again find the principle of the Heat transfer device, and named as Heat Pipe, Heat Pipe), the first successfully applied in aerospace technology, which attracts scholars after the great interest and attention.
If one end of a heat pipe is heated and the other is cooled, and the middle part is insulated with some material, a two-part heat transfer process will begin inside the heat pipe.Heating section of the working medium will boil or evaporation, the absorption of latent heat of gasification from liquid to steam, the steam produced in the pipe must be under the action of pressure difference, flowing to the cooling section, steam condenses into liquid, encounter cold wall will also release of latent heat of gasification through the wall to the outside cold source, the liquid condensed down * pipe inner surface of porous material produced by the capillary force fed back to the heating period, start evaporation heat absorption process, in this way, through the league continued phase change of working medium inside, completed the continuous transfer of heat.
The structure of the heat pipe is divided into three areas according to the axis: heating section (evaporation section), adiabatic section and cooling section (condensation section);From the cross section of the heat pipe, it can also be divided into three parts: the shell, the suction core, (filled with working medium) and the steam flow channel in the middle.Heat pipe shell is commonly cylindrical containers, also can according to need to make other shapes, such as flat shape, ring, etc., close to the lining of the porous material called liquid-core absorption, absorption of liquid-core capillary force is the main purpose of the condensate from the condensate back to evaporation section, as a kerosene lamp wick kerosene can be from the bottom up.The use of capillary force to return liquid is the main characteristic of a standard heat pipe, that is, a standard heat pipe is a heat pipe with a certain core structure.There are many structure types of liquid core, mainly the following categories: one is uniform core, such as in the inner wall with a very fine wire mesh or sintering on a layer of porous material;The second kind is groove core, namely in the pipe inner surface processing on the very fine axial groove or threaded groove;The third type is the composite core, that is, the outside of the channel core with a screen core;The fourth type is the main road core, that is, a thin pipe is placed inside the heat pipe, which is specially used for reflux liquid. The structural characteristics of several types of suction cores are shown in the figure.
When the heat pipe is used on the surface, gravity can be used to help the condensate return. In this case, the heat pipe can be tilted, with the heating section at the bottom and the cooling section at the top. Such heat pipe is called gravity assisted heat pipe, as shown in the figure below.Since gravity can aid reflux, the requirement for the suction core is greatly reduced.If the heat pipe is placed vertically, the liquid core is not added in the pipe, and the liquid is completely returned by gravity, such a heat pipe is also called a thermosyphon.Thus, the thermosyphon is simple in structure, easy to manufacture and low in cost, so it is widely used in energy saving projects.
Heat pipe due to the phase change heat transfer working medium, thus has excellent heat transfer performance, if will be a heat pipe with exactly the same shape size a copper bar, insert them at the same time at the end of the heat source, when both pass the same power, axial isothermal heat pipe has good sex, while copper bar has obvious temperature down, as shown, so the heat transfer characteristics of heat pipe can so to describe: it can transfer a lot of heat under small temperature difference.The thermal conductivity of the heat pipe can be dozens or even hundreds of times higher than the copper with good thermal conductivity, so it is called the superconducting heat body.
