The heat dissipation efficiency is poor. Is the selection of air supply form of fan correct?

Axial flow fan and centrifugal fan

The most extensive form is to use axial fan to blow air down

The heat dissipation efficiency is poor. Is the selection of air supply form of fan correct?

Axial flow fan and centrifugal fan

The most extensive form is to use axial fan to blow air downward (taking CPU heat dissipation as an example), which is so popular because of its good comprehensive effect and low cost. In addition, it seems to be more and more common to reverse the direction of axial flow fans and turn them into upward ventilation.

The difference between the two air supply forms lies in the different air flow forms. Turbulence is generated when blowing, and the wind pressure is high, but it is easily lost by resistance. When the air is discharged, laminar flow is generated, and the wind pressure is small but the airflow is stable. Theoretically, the heat transfer efficiency of turbulence is much higher than that of laminar flow, so it has become the mainstream design form. But the movement of airflow is also directly related to the heat sink. In some heat sink designs (such as the heat sink is too tight), the airflow is greatly hindered by the heat sink, and it may be better to use exhaust air at this time.

This proves that it is a good reason to obtain the cooling capacity of fin evaporator by ventilation. As for the design of side blowing, it is usually no different from the effect of top blowing.

The axial flow fan is blocked by the position of the motor, and the airflow cannot pass through the middle of the blowing area smoothly, which is called "dead zone". On a typical radiator, the middle radiator has the highest temperature. Because of this contradiction, when using axial fan, the heat dissipation effect of radiator is not sufficient.

Centrifugal fan is a completely different blowing form from axial fan, which is gradually used in CPU heat dissipation and is usually called "turbofan" by computer users. The advantage of this kind of fan is that it solves the problem of "dead zone" well. The centrifugal fan is different from the traditional fan in that its blades rotate in a vertical plane and the air inlet is located at the side of the fan. The airflow received by the bottom surface of the radiator is evenly distributed.

There is no obstacle to the blowing direction of the centrifugal fan, so there is the same airflow at all positions. At the same time, it has a wider adjustment range of wind pressure and air volume, and the speed regulation effect is better. The negative impact is the same as that of high-power axial fan-high price and high noise.

Parallel connection and series connection of fans

Parallel operation means using two or more fans in parallel. ?

Under the condition of free space, the air volume produced by two fans in parallel is only twice that of a single fan. When the parallel fan is used under the condition of high system impedance, the higher the system impedance, the lower the air volume that the parallel fan can increase. Therefore, parallel application is recommended only when the system impedance is low, that is, when the fan runs almost completely under free air supply.

Series operation refers to the use of two or more fans in series. ?

The static pressure generated by two fans in series can be doubled under the condition of zero air volume, but the air volume cannot be increased under the condition of free space. In the system with high static pressure, adding series fans can increase the air volume.

Therefore, for systems with high system impedance, series operation can achieve the highest effect. ?