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What types of cooling fans are usually divided into

Time:2022-03-28 Views:3

What types of cooling fans are usually divided into

Cooling fans are generally divided into the following three categories:
1 axial flow type: the direction of the air outlet is the same as the axial direction.
2 centrifugal: use centrifugal force to throw the air flow outward along the blade.
3. Mixed flow type: it has the above two air flow modes.
Principle of cooling fan
Principle: the working principle of the fan is realized according to the energy conversion, namely: electric energy → electromagnetic energy → mechanical energy → kinetic energy. The circuit principle is generally divided into various forms. The performance of the fan will be different with different circuits.
Composition of axial flow fan:
Fan frame, fan blade, bearing, PCB control circuit, drive motor
Speed refers to the speed at which the fan rotates. It is usually measured by the number of turns in 1 minute, i.e. rpm. The rotating speed is related to the number of electromechanical winding turns, wire diameter, outer diameter and bottom diameter of fan blade impeller, blade shape and bearings used. When the rotating speed increases, the air volume increases accordingly.
The speed value represents the air volume to a certain extent. Under certain conditions, the higher the speed, the noise and vibration will increase accordingly. Therefore, when the air volume meets the heat dissipation requirements, the low speed fan should be used as far as possible. General speed (taking DC axial fan as an example): 2510 fan 7000 ~ 12000rpm; 3010 fan 5000 ~ 9000rpm; 4010 fan 5000 ~ 7000rpm; 5010 fan 3500 ~ 5000rpm; 6025 fan 2600 ~ 4500rpm; 7025 fan 2400 ~ 3600rpm; 8025 fan 2000 ~ 3500rpm; 9225 fan 1600 ~ 3100rpm; 12025 fan 1500 ~ 2500rpm; 12038 fan 2000 ~ 3200rpm.
The fan speed can be tested by BIOS when starting the computer, or by the monitoring software of other motherboards; It can also be tested by the speed tester. Note: the first two methods can only be measured by the fan that supports the speed measurement function.
Air volume and pressure:
There are two test methods for air volume and air pressure. One is to test with wind tunnel instrument, and the other is to test with double box method. But for ordinary users, there is no such device. Only the data provided by the manufacturer can be used as a reference, and the final cooling effect depends on it.
Air volume: air volume refers to the product of fan ventilation area and plane speed. The ventilation area is the outlet area minus the projected area at the vortex tongue. Plane velocity is the velocity of gas flowing through the whole plane, and the unit is m3 / s. When the plane speed is constant, the larger the outer diameter of the fan blade impeller, the larger the ventilation area and the larger the air volume. The plane speed is determined by the rotor speed and wind pressure. When the ventilation area is certain, the greater the plane speed is, the greater the air volume is. The larger the air volume, the greater the heat absorption of the air. When the air flows and transfers, it can take more heat around, and the more obvious the fan heat effect is
Wind pressure: in order to carry out normal ventilation, it is necessary to overcome the resistance in the ventilation stroke of the fan. The fan must produce the pressure to overcome the air supply resistance. The measured change value of the pressure is called static pressure, that is, the differential pressure between the maximum static pressure and atmospheric pressure. It is the pressure of gas acting parallel to the surface of an object, and the static pressure is measured through a hole perpendicular to its surface. The kinetic energy needed in the gas flow is converted into the form of pressure, which is called dynamic pressure.
In order to achieve the purpose of air supply, static pressure and dynamic pressure are required. The total pressure is the algebraic sum of static pressure and dynamic pressure. The total pressure refers to the total pressure increase given by the fan, that is, the difference between the total pressure at the outlet and inlet of the fan. In practical application, the nominal maximum air volume is not the air supply volume obtained by the actual fan heat sheet. Large air volume does not mean strong ventilation capacity. When the air flows, the air flow will encounter the obstruction of fan thermal inspection sheet or element in its flow path, and its impedance will restrict the free flow of air. That is, when the air volume increases, the air pressure will decrease. Therefore, there must be an optimal operating point, that is, the intersection of fan performance curve and wind resistance curve. At the operating point, the slope of the fan characteristic curve is the smallest, and the change rate of the system characteristic curve is the lowest. Note the static efficiency (air volume) of the fan at this time × Wind pressure ÷ power consumption) is the best. Of course, sometimes in order to reduce the system impedance, even select a smaller fan to obtain the same air volume.

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