With the continuous evolution of LED explosion-proof lamp materials and packaging technology, the brightness of LED explosion-proof lamps has been continuously improved. . However, the problem of heat dissipation is the main obstacle to the development of LED explosion-proof lamps as lighting objects. Let us introduce several heat dissipation methods and heat dissipation materials.
Cooling method
Generally speaking, radiators can be divided into active cooling and passive cooling according to the way of removing heat from the radiator. The so-called passive heat dissipation means that the heat of the heat source LED light source is naturally dissipated into the air through the heat sink. It is often used in equipment that does not require space, or to dissipate heat for components that generate little heat. For example, some popular motherboards also adopt passive cooling on the north bridge, and most of them adopt active cooling. Active cooling is The heat emitted by the heat sink is forcibly taken away by cooling devices such as fans, which are characterized by high heat dissipation efficiency and small size of the device.
Active cooling can be divided into air cooling, liquid cooling, heat pipe cooling, semiconductor cooling, chemical cooling and so on.
Air-cooled air-cooled heat dissipation is the most common heat dissipation method, and in comparison, it is also a cheaper method. Air cooling is essentially the use of fans to take away the heat drawn by the radiator. It has the advantages of relatively low price and convenient installation. However, it is highly dependent on the environment, such as the temperature rise and its cooling performance will be greatly affected when overclocking.
liquid cooling
Liquid-cooled heat dissipation is the forced circulation of liquid driven by the pump to take away the heat of the radiator. Compared with air-cooled, it has the advantages of calmness, stable cooling, and less dependence on the environment. The price of liquid cooling is relatively high, and the installation is relatively troublesome. At the same time, try to install according to the method instructed in the manual to obtain the cooling effect. For reasons of cost and ease of use, liquid-cooled heat dissipation usually uses water as the heat transfer liquid, so liquid-cooled radiators are often referred to as water-cooled radiators.
Heat pipe
The heat pipe is a heat transfer element, which fully controls the principle of heat conduction and the rapid heat transfer properties of the refrigeration medium, and transfers heat through the evaporation and condensation of the liquid in the fully enclosed vacuum tube. The heat transfer area on both sides of the hot and cold can be changed arbitrarily, the heat transfer can be carried out at a distance, and the temperature can be controlled, and the heat exchanger composed of heat pipes has the advantages of high heat transfer efficiency, compact structure, and low fluid resistance loss, etc. Strengths. Its thermal conductivity far exceeds that of any known metal.
Semiconductor refrigeration
Semiconductor refrigeration is to use a special semiconductor refrigeration sheet to generate a temperature difference when it is energized to cool. As long as the heat at the high temperature end can be effectively dissipated, the low temperature end will be continuously cooled. A temperature difference is generated on each semiconductor particle, and a refrigerating sheet is made up of dozens of such particles in series, so that a temperature difference is formed on the two surfaces of the refrigerating sheet. By manipulating this temperature difference phenomenon and cooling the high temperature end with air cooling/water cooling, an excellent heat dissipation effect can be obtained. Semiconductor refrigeration has the advantages of low refrigeration temperature and high reliability. The temperature of the cold surface can reach below minus 10°C, but the cost is too high, and short circuit may be formed due to too low temperature, and the technology of semiconductor refrigeration chip is not mature enough. it works.
chemical refrigeration
The so-called chemical refrigeration is to use some ultra-low temperature chemicals and manipulate them to absorb a lot of heat when they melt to reduce the temperature. The use of dry ice and liquid nitrogen is more common in this regard. For example, the use of dry ice can reduce the temperature to below minus 20 ℃, and some more "" players manipulate liquid nitrogen to reduce the CPU temperature to below minus 100 ℃ (theoretically), of course, due to the high price and too short duration, this method More common in labs or extreme overclockers.
Material selection
Thermal conductivity (unit: W/mK)
Silver 429
Copper 401
Gold 317
Aluminum 237
Iron 80
Lead 34.8
1070 type aluminum alloy 226
1050 type aluminum alloy 209
6063 type aluminum alloy 201
6061 type aluminum alloy 155
Generally speaking, the general air-cooled radiator should naturally choose metal as the material of the radiator. For the selected material, it is expected that it has high specific heat and high thermal conductivity at the same time. It can be seen from the above that silver and copper are the best thermal conductive materials, followed by gold and aluminum. But gold and silver are too expensive, so at present, the heat sinks are mainly made of aluminum and copper. In comparison, both copper and aluminum alloys have their own advantages and disadvantages: copper has good thermal conductivity, but it is expensive, difficult to process, heavy, and copper radiators have a small heat capacity and are easy to oxidize. On the other hand, pure aluminum is too soft to be used indirectly. Only aluminum alloys are used to provide sufficient hardness. The advantages of aluminum alloys are low price and light weight, but their thermal conductivity is much worse than copper. Therefore, the following materials have also appeared in the growth history of radiators:
Pure aluminum radiator
Pure aluminum radiator is the most common radiator in the early days. Its manufacturing process is simple and the cost is low. So far, pure aluminum radiator still occupies a considerable part of the market. In order to increase the heat dissipation area of its fins, the most commonly used processing method for pure aluminum radiators is aluminum extrusion technology, and the main indicators for evaluating a pure aluminum radiator are the thickness of the radiator base and the Pin-Fin ratio. Pin refers to the height of the fins of the heat sink, and Fin refers to the interval between two adjacent fins. The Pin-Fin ratio is the height of the Pin (excluding the thickness of the base) divided by the Fin. The larger the Pin-Fin ratio, the larger the effective heat dissipation area of the radiator, and the more advanced the aluminum extrusion technology.
Pure copper radiator
The thermal conductivity of copper is 1.69 times that of aluminum, so other things being equal, a pure copper heat sink can take heat away from the heat source faster. However, the texture of copper is a problem. Many advertised "pure copper heat sinks" are not really 100% copper. In the list of copper, copper with a copper content of more than 99% is called acid-free copper, and the next grade of copper is Dan copper with a copper content of less than 85%. At present, the copper content of most pure copper radiators on the market is between the two. And some inferior pure copper radiators contain less than 85% of copper. Although the cost is very low, their thermal conductivity is greatly reduced, which affects the heat dissipation. In addition, copper also has obvious shortcomings, such as high cost, difficult processing, and too much mass of the heat sink, which hinder the application of all-copper heat sinks. The hardness of red copper is not as good as that of aluminum alloy AL6063, and the performance of some mechanical processing (such as grooving) is not as good as that of aluminum; the melting point of copper is much higher than that of aluminum, which is not conducive to extrusion and other problems.
Copper-aluminum bonding technology
After considering the respective shortcomings of copper and aluminum, some high-end radiators in the market often use a copper-aluminum combination manufacturing process. These heat sinks usually use copper metal bases, while heat sink fins use aluminum alloys. Of course, in addition to the copper bottom, there are also methods such as the use of copper pillars for the heat sink, which is also the same principle. With high thermal conductivity, the copper bottom surface can quickly absorb the heat released by the CPU; the aluminum fins can be made into the most favorable shape for heat dissipation by means of complex processes, and provide a large heat storage space and release it quickly. A balance has been found in all aspects.
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