As one of the essential materials for active cooling, the performance of the cooling fan is absolutely a common concern of customers, but many customers do not know how to understand the performance indicators of the cooling fan.
Speed is one of the fundamental determinants of fan performance indicators. The unit of fan speed is rpm. Chinese manufacturers generally use R / min to express it. In fact, the meaning of the expression is the same, which refers to the number of fan blades rotating per minute. The fan speed is determined by the number of fan blades and the internal line of the motor
The number of turns is related to the working voltage, but not necessarily to the quality of the fan.
II. Air volume
Air volume is the most important index to measure the cooling capacity of cooling fan. Air volume refers to the total volume of air discharged or incorporated by the cooling fan per minute. CFM (cubic foot per minute) is generally used as the air volume unit. The larger the air volume is, the higher the cooling capacity of the cooling fan is. Under the same air volume, the cooling effect is also related to the flow mode of the wind.
Three. Wind pressure
Air pressure and air volume are relative concepts. In order to make the fan have larger air volume, sometimes it needs to sacrifice some air pressure to complete. If a cooling fan can drive a lot of air flow, but the wind pressure is small, the wind will not blow to the bottom of the radiator, so we often find that some fans in our life have high speed and large air volume, but the cooling effect is not particularly good, because the wind pressure is low.
The noise of cooling fan is the noise produced when the fan is working, which is affected by many factors, and the unit is dB. The noise of cooling fan is related to friction, air flow, self vibration and other factors. The higher the fan speed, the greater the air volume, the greater the noise. What are the main causes of fan noise
If the physical center of mass of the rotor and the inertia center of the rotor are not on the same axis when the fan rotor is rotating, the rotor will be unbalanced. The closest distance between the physical mass center of the rotor and the inertia center of the shaft is called eccentricity, which is caused by the imbalance of the rotor. When the rotor is rotating, a force is generated on the shaft bracket due to the centrifugal force, and the vibration is transmitted to all parts of the machine through the base path.
2. Wind noise
When the fan works, the blade periodically bears the pulsating force of the uneven air flow at the outlet, resulting in noise; on the other hand, due to the uneven distribution of the pressure on the blade itself and on the blade, the disturbance to the surrounding gas and parts during the rotation also constitutes the rotating noise; in addition, the turbulence attachment layer, vortex and vortex separation caused by the gas flowing through the blade cause the pressure on the blade It is pulsation that produces eddy noise. Generally, the fan with larger air volume and air pressure will also have larger cutting noise.
3, abnormal sound
When the fan is running, in addition to the wind sound, if there are other sounds, it can be judged that the fan has abnormal sound. Abnormal sound may be caused by foreign matters or deformation in the bearing, as well as collision due to improper assembly, resulting in uneven winding of motor winding, resulting in looseness, which may cause abnormal sound.
V. service life
Generally speaking, the service life of the cooling fan will be affected by the use environment and working pressure. If the cooling fan works in a high temperature working environment, it will accelerate the evaporation of lubricating fluid in the oil bearing, increase the friction of the device expansion, increase the coil resistance, fall into a vicious cycle of increased heat and temperature, and accelerate the aging of electronic components. The dust will change the mass distribution of the blades, increase the friction, increase the wind resistance, affect the heat dissipation, hinder the heat exchange between the fins and the air, and generate the electrostatic discharge to damage the components and equipment. The bad use environment may make the effect of the fan greatly reduced, and the service life greatly reduced. If the working pressure of the cooling fan is large, the faster the fan speed is, the faster the bearing wear is, the more the stator winding coil and electronic components heat up, and the shorter the service life is.
Vi. air supply mode
1. Axial flow fan
The most widely used is to use axial-flow fan to blow down. The reason why it is so popular is that the comprehensive effect is good and the cost is low. In addition, there is also the reverse direction of axial flow fan, into the form of up pumping, which seems to be more and more common. Although axial-flow fans are widely used, there are inherent defects. The axial-flow fan is blocked by the motor position, and the air flow cannot flow smoothly through the middle of the blowing area, which becomes the dead zone. On a typical fin, the middle fin has the highest temperature. Because of this contradiction, the heat dissipation effect on the heat sink is not enough when adopting this axial flow fan.
2. Centrifugal fan
Centrifugal fan is totally different from axial-flow fan in the form of blowing. The difference is that its blades rotate in a vertical plane, and the air inlet is located on the side of the fan. The air distribution received at the bottom of the radiator is even, the air inlet is located at the side of the fan, the air distribution received at the bottom of the radiator is even, there are no obstacles in the direction of the centrifugal fan's blowing, so there are the same air bubbles at all positions. At the same time, its air pressure and air volume regulation range is larger, the speed control effect is better, the negative impact is the same as the high-power axial-flow fan, the price is high, the noise is big.
3. Design of other improved air ducts
Another way to solve the wind blind area is to change the direction of the fan. The traditional installation method is that the air flow is downward. After improvement, the fan is changed to lateral blowing to completely solve the wind blind area. Another advantage is that there is no rebound wind pressure (usually when blowing downward