Airflow

The airflow of cooling fan refers to the total airflow of air discharged or absorbed by the cooling fan per minute. If calculated in cubic meters, it's the CMM. The airflow unit often used by cooling fans is CFM (about 0.028 m3 / min).

Large air volume fan, airflow is the most important index to measure the cooling capacity of cooling fans. Obviously, the larger the airflow, the higher the cooling capacity of cooling fans. This is because the heat capacity ratio of air is certain, and the larger the airflow, that is, more air can take more heat per unit time. Of course, under the same airflow, the cooling effect is related to the air flow mode.

Pressure

Pressure and airflow are two relative concepts. Generally speaking, in the consideration of cost saving, to design a fan with large airflow, it is necessary to sacrifice some air pressure. If the fan can drive a large amount of air flow, but the pressure is small, the air will not blow to the bottom of the radiator (this is why some fans have high speed and large airflow, but the cooling effect is not good). On the contrary, large air pressure often means that the airflow is small, and there is not enough cold air for heat exchange with the radiator, which will also cause poor cooling effect

Speed

High speed fan, the fan speed refers to the number of times the fan blades rotate per minute, the unit of speed is rpm. The speed of the fan is determined by the number of turns of the coil in the motor, the operating voltage, the number of fan blades, the inclination angle, the height, the diameter and the bearing system. There is no necessary relationship between speed and fan quality. The speed of the fan can be measured through the internal speed signal, or through the external measurement.

Noise

Low noise fan, besides the cooling effect, the noise of fan is also a common concern. Fan noise is the noise produced by fan when it works, which is affected by many factors, the unit of noise is dB. The noise measurement of fan should be carried out in the noise chamber with noise less than 17dB, one meter away from the fan, and the fan air inlet should be aligned along the direction of the fan axis. A weighted method is adopted for measurement. The spectrum characteristics of fan noise are also very important. Therefore, it is necessary to record the noise frequency distribution of fans with a spectrometer. Generally, it is required that the noise of fans should be as small as possible and there should be no abnormal sound.

Fan noise is related to friction and air flow. The higher the fan speed and the larger the airflow, the greater the noise will be caused, and the vibration of the fan itself is also an important factor. Of course, the vibration of high quality fans will be very small, but the first two are difficult to overcome. To solve this problem, we can try to use larger fans. The working noise of large fan at lower speed shall be less than that of small fan at high speed under the same airflow. Another factor that we can easily ignore is the bearing of the fan. Because the rotor and bearing must be friction and collision when the fan is rotating at high speed, it is also a main source of fan noise.