What Is a Heat Pipe?
Heat pipe technology is a heat transfer element called "heat pipe" invented by George Grover of Los Alamos National Laboratory in 1963, which makes full use of the principle of heat conduction and phase change media The fast heat transfer property of the heat transfer object through the heat pipe to the heat source quickly, its thermal conductivity exceeds the thermal conductivity of any known metal.
- Heat pipe technology has been widely used in aerospace, military and other industries before. Since its introduction into the radiator manufacturing industry, people have changed the design of traditional radiators. The single heat dissipation mode and the use of heat pipe technology enable the radiator to achieve satisfactory results even with low-speed and low-air-volume motors, so that the noise problems that plague air-cooling and heat dissipation can be well resolved, opening up a new world of heat dissipation industry. Now common on CPU coolers. From a thermodynamic point of view, why does a heat pipe have such a good thermal conductivity? The endothermic and exothermic objects are relative. Whenever there is a temperature difference, the phenomenon of heat transfer from high temperature to low temperature is bound to occur. From the three ways of heat transfer (radiation, convection, conduction), convection conduction is the fastest. The heat pipe is a phase change process that uses the medium to evaporate on the hot side and condense on the cold side (that is, uses the latent heat of liquid evaporation and the latent heat of condensation) to make heat transfer quickly. The general heat pipe is composed of a shell, a wick and an end cap. The inside of the heat pipe is pumped into a negative pressure state and filled with an appropriate liquid. This liquid has a low boiling point and is easily volatile. The tube wall has a liquid wick, which is composed of a capillary porous material. One end of the heat pipe is an evaporation end, and the other end is a condensing end. When one end of the heat pipe is heated, the liquid in the capillary tube rapidly vaporizes, and the steam flows to the other end under the power of heat diffusion, and condenses to release heat at the cold end. Capillary flow back to the evaporation end, so the cycle continues until the temperature of the two ends of the heat pipe is equal (at this time the steam thermal diffusion stops). This cycle is fast and heat can be conducted continuously. [1]
- A typical heat pipe consists of a shell, a wick, and an end cap. The inside of the pipe is drawn to 1.3 × (
- In the evaporation section of the heating heat pipe, the working liquid in the core is heated to evaporate and take away the heat. This heat is the latent heat of evaporation of the working liquid. The steam flows from the central channel to the condensation section of the heat pipe, condenses into a liquid, and releases latent heat at the same time. Under the action of force, the liquid returns to the evaporation section. In this way, a closed cycle is completed, thereby transferring a large amount of heat from the heating section to the heat dissipation section. When the heating section is below and the cooling section is above, and the heat pipe is placed vertically, the return of the working liquid can be satisfied by gravity. There is no need for a capillary tube core. This type of heat pipe without a porous body core is called a thermosiphon. The thermosiphon has a simple structure and is widely used in engineering. [1]
- The heat pipe is a heat transfer element that relies on the phase change of the internal working liquid to achieve heat transfer, and has the following basic characteristics.
- The compatibility of the heat pipe means that within the expected design life of the heat pipe, the working liquid in the pipe does not undergo significant chemical reactions or physical changes with the shell, or there are changes but not enough to affect the performance of the heat pipe. Compatibility has important significance in the application of heat pipes. Only heat pipes with good long-term compatibility can ensure stable heat transfer performance, long-term working life, and the possibility of industrial applications. Carbon steel-water heat pipe is a chemical treatment method that effectively solves the problem of chemical reaction between carbon steel and water, which makes carbon steel-water heat pipe a high-performance, long-life, low-cost heat pipe. Scale promotion and use. There are many factors that affect the life of a heat pipe. In summary, the main forms of incompatibility of effective tubes are the following three aspects, namely: the generation of non-condensable gases; the deterioration of the thermal properties of the working liquid; and the corrosion and dissolution of the shell material. Produce non-condensable gas. The non-condensable gas is generated due to the chemical reaction or electrochemical reaction between the working liquid and the shell material. When the heat pipe works, the gas is swept by the steam flow to the condensing section to form an air plug. The effective condensation area is reduced, the thermal resistance is increased, the heat transfer performance is deteriorated, the heat transfer capacity is reduced or even fails. Deterioration of the working fluid's physical properties The organic working medium will gradually decompose at a certain temperature. This is mainly due to the unstable nature of the organic working fluid or the chemical reaction with the shell material, which causes the working medium to change its physical properties, such as toluene, Organic working liquids such as alkanes and hydrocarbons are prone to this type of incompatibility. (3) Corrosion and dissolution of the shell material The working fluid continuously flows in the shell. At the same time, there are factors such as temperature differences and impurities, which cause the shell material to dissolve and corrode, increasing flow resistance, and reducing heat transfer performance of the heat pipe. When the tube shell is corroded, the strength is reduced, and even the corrosion perforation of the tube shell is caused, making the heat pipe completely ineffective. This kind of phenomenon often occurs in high temperature heat pipes of alkali metals. [1]
Heat pipe wick type heat pipe
- As mentioned earlier, the three main components that make up a heat pipe are the shell, die, and working fluid. During the design process, the materials of the shell and die can be selected after a reasonable selection and production can begin. Generally, the manufacturing process of the heat pipe includes the following process operations and is performed according to a certain procedure. 1. Machining-2.-Cleaning-3-Die making-4-Cleaning-5.-Welding-6-Leak detection-7-Degassing-8- Leak detection-9, filling-10, sealing-11, 11-baking-12, the actual manufacturing inspection often can reach 20, even hundreds of processes. Here are just the simplest necessary procedures. [1]
Heat pipe gravity heat pipe
- Gravity heat pipe is mainly composed of tube shell, end cap and working medium. Its general manufacturing process is as follows: 1. Mechanical processing (tube shell, end cap, or direct procurement)-2. Pre-treatment (tube shell, end cap except Oil derusting)-3, drying-4, end cap welding (argon arc welding, welding seam grinding)-5, filling working medium-6, exhaust air (baking)-7, head Welding (argon arc welding)-8. The key inspection procedures are: 6. Exhaust air, 7. Welding of the head [1]