With the enhancement of computing power in electronics, electrical appliances, and PCs, heat dissipation technology has increasingly become an unavoidable issue for power consumption and heat dissipation. Generally speaking, the major heat sources in a PC include CPU, motherboard (South Bridge, North Bridge and VRM part), graphics card and other components such as hardware, optical drive, etc. A considerable part of the electrical energy consumed when they work is converted into heat.
Definition of cooling technology
We all know that the operating temperature of electronic devices directly determines their service life and stability. To keep the operating temperature of the PC components within a reasonable range, in addition to ensuring that the temperature of the PC's working environment is within a reasonable range, it must also be treated with heat dissipation. Especially for the CPU, if the user has overclocked, to ensure its stable work, it must effectively dissipate heat.
Principle of heat transfer
Although we often refer to heat as thermal energy, heat is not strictly a kind of energy, but just a way of transferring energy. From a microscopic point of view, after the molecules in the region are impacted by external energy, they are transferred from the regions with high energy to molecules with low heat energy. Therefore, it is generally believed that the transfer of energy is heat. Of course, the most important process or form of heat is heat transfer.
Way of heat transfer
Friends who have studied middle school physics know that there are three main ways of heat transfer:
Heat Conduction :
The transfer of energy between the substance itself or when it comes into contact with the substance is called heat conduction. This is the most common method of heat transfer, in which particles with lower energy and particles with higher energy directly contact and collide to transfer energy. Relatively speaking, the heat conduction method is limited to solid and liquid, because the molecular composition of gas is not very tight, and the energy transfer between them is called thermal diffusion.
The basic formula of heat conduction is "Q=K×A×ΔT/ΔL". Where Q represents heat, which is the heat generated or conducted by heat conduction; K is the thermal conductivity of the material, which is similar to the specific heat, but has some differences from the specific heat. The thermal conductivity is inversely proportional to the specific heat. The higher the thermal conductivity, the lower the specific heat value. For example, the thermal conductivity of pure copper is 396.4, and its specific heat is 0.39; In the formula, A represents the area of heat transfer (or the contact area between two objects), and ΔT represents the temperature difference between the two ends; ΔL is the distance between the two ends. Therefore, from the formula, we can find that the amount of heat transfer is proportional to the thermal conductivity and heat transfer area, and inversely proportional to the distance. The higher the heat transfer coefficient, the larger the heat transfer area, and the shorter the transmission distance, the higher the heat transfer energy, and the easier it is to take away heat.
Heat convection:
Convection refers to the heat transfer method in which fluid (gas or liquid) comes into contact with a solid surface, causing the fluid to remove heat from the solid surface.
In terms of specific application, there are two different situations of thermal convection, namely: natural convection and forced convection. Natural convection refers to fluid movement, which is caused by temperature differences. Fluids with higher temperatures have lower density, so they are lighter and move upward relatively. Conversely, a fluid with a low temperature has a high density and therefore moves downward. This kind of heat transfer is because after the fluid is heated, or there is a temperature difference, the heat transfer power is generated; Forced convection means that the fluid is forced externally (such as air flow driven by a fan). Wherever the driving force goes, the fluid moves where, so this kind of thermal convection is more efficient and directable.
The formula for heat convection is "Q=H×A×ΔT". In the formula, Q still represents heat, which is the heat taken away by thermal convection; H is the value of thermal convection coefficient, and A represents the effective contact area of thermal convection; ΔT represents the temperature difference between the solid surface and the area fluid. Therefore, in heat convection transfer, the amount of heat transfer is directly proportional to the heat convection coefficient, effective contact area and temperature difference; The higher the thermal convection coefficient, the larger the effective contact area, and the higher the temperature difference, the more heat can be taken away.
Heat radiation :
Thermal radiation is a transfer method that allows heat exchange to occur without any medium without contact. In other words, thermal radiation is actually a wave form to achieve the purpose of heat exchange.
Since heat radiation is transmitted by waves, it is bound to have wavelengths and frequencies. The heat absorption rate of the object required without passing through the medium determines the efficiency of the transfer. There is a thermal radiation coefficient, whose value is between 0 and 1, which belongs to the surface characteristics of the object, while the thermal conductivity coefficient of a rigid body is the material characteristic of the object. The general heat conduction formula of heat radiation is "Q = E × S × F × Δ (Ta-Tb)". In the formula, Q represents the exchange capacity of heat radiation, and E is the heat radiation coefficient of the surface of the object. In practice, when the substance is metal and the surface is smooth, the thermal emissivity coefficient is relatively small, and the surface thermal emissivity value will increase after the metal surface is processed (such as coloring). Most of the thermal emissivity values of plastics or non-metals are relatively high. S is the surface area of the object, and F is the functional relationship between the angle of radiant heat exchange and the surface, but this function is more difficult to explain here. Δ(Ta-Tb) is the temperature difference between the temperature of surface a and surface b. Therefore, there is a proportional relationship between the thermal radiation coefficient, the size of the surface area of the object, and the temperature difference.
Any radiator will also use the above three heat transfer methods at the same time, but the emphasis is different. Taking CPU heat dissipation as an example, heat is continuously emitted by the CPU work, and is transferred to the heat sink by conduction through the heat sink base in close contact with its core. Then, the heat that reaches the heat sink is sent away by other means such as fan blowing. The entire heat dissipation process includes 4 links:
The first is the CPU, which is the heat generator;
The second is the heat sink, which is a heat conductor;
The third is the fan, which is a medium to increase heat conduction and direct heat conduction;
The fourth is air, which is the final flow direction of heat exchange.
Generally speaking, according to the way the heat is taken away from the heat sink, the heat sink can be divided into active heat dissipation and passive heat dissipation.
The so-called passive heat dissipation means that the heat generated by the heat source such as the CPU is naturally dissipated into the air through the heat sink. The heat dissipation effect is proportional to the size of the heat sink, but because it naturally emits heat, the effect is of course greatly reduced. It is often used in equipment that does not require space, or to dissipate heat for components that do not generate much heat. For example, some popular motherboards also adopt passive cooling on the north bridge. For personal PCs, most of them adopt active cooling methods. Active cooling is to forcefully take away the heat emitted by the heat sink through cooling devices such as fans. It is characterized by high heat dissipation efficiency and small size of the equipment.
