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Principle and basic mode of heat transfer for high power LED lighting

From: Data:30/08/2016

learned physics friends all know, heat transfer are mainly in three ways: first, conduction: material itself or when the material is in contact with the material, energy transfer is called heat conduction. This is most commonly a heat transfer, by lower energy particles and particles of a higher amount of direct contact to transmit energy. In contrast, the heat transfer is confined to the solid and liquid, because the molecular composition of the gas is not very tight, the transfer of energy between them is called thermal diffusion. The basic formula of heat conduction is “ Q=K× A× T/Δ Δ L”. Where Q represents for the heat, is also the heat conduction generated or conduction of heat; K for the thermal conductivity of materials, heat conduction coefficient similar to the specific heat, but and the specific heat have some differences, inversely proportional to the thermal conductivity and specific heat, heat conduction coefficient is high, its specific heat values is low. For example, the thermal conductivity of pure copper was 396.4, and its specific heat is 0.39; formula on behalf of a heat transfer area (or the contact area of the two objects), Δ t on behalf of both ends of the temperature difference; Δ L is the distance between the two ends of. Therefore, from the formula we can find that the heat transfer coefficient, heat transfer coefficient, heat transfer area is proportional to the same distance is inversely proportional to the. The higher the heat transfer coefficient, the greater the heat transfer area, the shorter the distance of the transmission, the higher the energy of heat transfer, it is easier to take away heat. Second convection: refers to the fluid (gas or liquid) and the solid surface contact, causing the fluid from the solid surface will be the tropical heat transfer. Specific application to the actual point of view, there are two different kinds of heat convection, namely: natural convection and forced convection. Natural convection refers to the fluid movement, the cause is the temperature difference, the temperature high fluid density is low, therefore the quality is light, relatively will move upward. Instead, the fluid with low temperature, high density and therefore downward movement, the heat transfer is because the heated fluid, or that there is temperature difference after the heat transfer of power; forced convection is fluid by external forcing (such as the fan driven air flow) and driving force to where, fluid to where motion, so more efficient thermal convection and directivity. The formula of heat convection is “ Q=H× A× Δ T”. In the formula Q still represent the heat is carried away by the thermal convection heat; h for heat convection coefficient, a representative the effective contact area of convection heat; Δ t on behalf of the solid surface and the area between the fluid temperature difference. So convective heat transfer, heat transfer with the same number of convection heat transfer coefficient, the effective contact area and temperature difference proportional relationship; heat convection coefficient is high, the effective contact area is greater, the difference in temperature is high, can take away the heat more. The third radiation: radiation heat is a can in the absence of any medium, do not need to contact can be occurred at a heat exchange transfer mode, that is to say, thermal radiation is actually in the form of wave reached the purpose of heat exchange. Since the thermal radiation is transmitted through the waves, so it would have wavelength and frequency. Not through the medium of transfer object that requires the heat absorption rate to determine the transfer efficiency of the, here there is a heat radiation coefficient, and its value between 0 and 1, is belongs to the characteristics of the object surface, and the thermal conductivity of a rigid body is the material properties of the object. The heat transfer formula of general heat radiation is Q; =E× S× “ F× Δ (Ta-Tb) ”. In the formula, Q represents the ability to exchange heat, and E is the heat radiation coefficient of the surface of the object. In practice, when the material is metal and the surface is bright and clean, the heat radiation coefficient is relatively small, and the surface of the metal processing (such as coloring) the surface heat radiation coefficient will increase. The majority of the heat radiation coefficient of plastic or non metal is higher. S is the surface area of the object, F is a function of the radiation heat exchange point of view and the surface, but this function is difficult to explain. Δ (Ta-Tb) is the temperature difference between the surface a and the surface B. Therefore, the heat radiation coefficient, the size of the object surface area and the temperature difference between the existence of a proportional relationship. Any heat sink will also use the above three kinds of heat transfer, but the focus is different. Bid farewell to the heat transferred to the CPU cooling, for example, the heat conduction process consists of four steps. The first is the CPU, it is the source of heat, heat from the CPU work constantly send out; the second is the base and the radiating fin is a heat conductor, the base and the CPU core closely contact with the heat sink base to the heat conduction of the heat sink; the third is the fan is to increase the heat conduction and pointing to the heat conduction medium to reach the heat sink through other ways such as fan blowing the heat; the fourth is air, which is heat exchange flows to the end, to ensure good heat dissipation, internal chassis have ample space and science of air duct.