Noise of cooling fan
Noise of cooling fan
Besides the heat dissipation effect, the fan noise is also a common concern.
Fan noise is the noise produced by fan when it is working. It is affected by many factors, and the unit is decibel (dB)The noise of the fan should be measured in the anechoic chamber with noise less than 17dB, one meter away from the fan,The fan inlet is aligned along the direction of the fan shaft, and the measurement is carried out in a weighted manner. The spectrum characteristic of fan noise is also very important, so it is necessary to use spectrum analyzer
Record the fan noise frequency distribution, generally require fan noise should be as small as possible, and there is no abnormal sound.
Fan noise and friction,
Air flow related. The higher the fan speed and the greater the air flow rate,The greater the noise, and the vibration of the fan itself is also not to be ignored factors. Of course, the high quality fan itself vibrates very little,
But the first two are insurmountable. To solve this problem, we can try to use larger fans.
Should be in the same amount of air,The working noise of large fan at low speed is smaller than that of small fan at high speedWorking noise.Another factor that we tend to overlook is the fan bearings.Because the fan rotates at high speed, the shaft and shaftThe friction between the bearings is a major source of fan noise.
The source of fan noise is：
1. vibration if the rotor of the fan rotates, the physical centroid of the rotor and the inertia center of the rotating shaft are not on the same axis,It can cause a rotor imbalance. The nearest distance between the physical center of mass and the inertia center of the rotor is called the eccentricity,The eccentricity of the rotor causes the eccentricity. When the rotor rotates, the force acting on the rotating shaft is generated due to the centrifugal force,The vibration passes through the base path to each part of the machine.
2. wind noise
When the fan works, because the blade periodically withstands the pulsating force of the uneven airflow in the outlet, it produces noise; on the other hand, the uneven distribution of the pressure on the blade itself and the blade,The disturbance of the surrounding gas and parts is also caused by the rotating noise when rotating; moreover, the turbulent flow is caused by the turbulence, the surface layer, the vortex and the vortex separation caused by the gas flowing through the bladeEddy current noise due to fluctuation of upper pressure distribution. The noise caused by these three reasons can be called synthetically
"Cut wind noise", fan with general air volume and high wind pressure, its cutting wind noise is also bigger.
3. different soundsThe wind noise only sounds simple, but the sound is different. When the fan is running, except the wind, if there are other sounds, it can be judged that the fan has abnormal sound. Abnormal sound may be due to foreign matter or deformation in the bearing, and improper assemblyWhen the collision occurs, or the winding of the motor winding is uneven, resulting in looseness, it may produce abnormal sound.