Cooling fans are usually divided into the following three categories:

1 Axial flow type: The direction of the air outlet is the same as that of the axis.

2 Centrifugal: Use centrifugal force to throw the air flow outward along the blades.

3 Mixed flow type: has the above two airflow methods.

 

The principle of the cooling fan:

 

Principle: The working principle of the fan is realized by energy conversion, namely: electric energy & rarr; electromagnetic energy & rarr; mechanical energy & rarr; kinetic energy. The circuit principle is generally divided into various forms, and the performance of the fan will be different if the circuit used is different.

 

The composition of the axial fan:

Fan frame, fan blade, bearing, PCB control circuit, drive motor

 

Speed:

Speed ​​refers to the speed at which the fan rotates, usually measured by the number of revolutions in 1 minute, namely: rpm. The speed is related to the number of turns of the electromechanical winding, the diameter of the wire, the outer diameter and the bottom diameter of the fan blade impeller, the shape of the blade and the bearing used. The increase in the speed increases the air volume correspondingly.

 

The speed value represents the size of the air volume to a certain extent. Under certain conditions, the higher the speed, the greater the noise and vibration. Therefore, when the air volume meets the heat dissipation requirements, a low-speed fan should be used as much as possible. . General speed (take 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 the BIOS when the computer is started, or by the monitoring software that comes with other motherboards; it can also be tested by the speed tester. Note: The first two methods must be a fan that supports the speed measurement function to be measured.

 

Air volume and pressure:

 

There are two test methods for air volume and wind pressure, one is to use a wind tunnel tester, and the other is to use a double-box method. But for the average user, there is no such device. It can only be used as a reference based on the data provided by the manufacturer, and then depends on the cooling effect.

 

Air volume: Air volume refers to the product of the plane speed of the fan's ventilation area. The ventilation area is the exit area minus the projected area at the vortex tongue. The plane velocity is the velocity of the gas moving through the entire 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 constant, the greater the plane speed, the greater the air volume. The greater the air volume, the greater the heat absorbed by the air, and the more heat can be taken away by the surrounding energy when the air moves, and the fan's thermal effect is more famous

 

Air pressure: In order to perform normal ventilation, it is necessary to overcome the resistance of the fan in the ventilation stroke. The fan must generate pressure to overcome the air supply resistance. The measured pressure change is called static pressure, which is the difference between large static pressure and atmospheric pressure. It is the pressure exerted by the gas on the surface parallel to the object, and the static pressure is measured through a hole perpendicular to the surface. The conversion of the kinetic energy required in the gas flow into the form of pressure 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 the static pressure and the dynamic pressure. The total pressure refers to the total pressure increase given by the fan, that is, the total pressure difference between the outlet and the inlet of the fan. In practical applications, the nominally large air volume value is not the air volume obtained by the actual fan heater. Large air volume does not mean that the ventilation capacity is strong. When the air flows, the airflow will encounter the obstruction of the fan heat check sheet or the component in its flow path, and its impedance will restrict the free circulation of the air. That is, when the air volume increases, the wind pressure will decrease. Therefore, there must be a suitable grass working point, that is, the intersection of the fan performance curve and the wind resistance curve. At the operating point, the slope of the fan characteristic curve is very small, while the rate of change of the system characteristic curve is very low. Note that the static efficiency of the fan at this time (air volume×wind pressure÷power consumption) is better. Of course, sometimes in order to reduce the system impedance, a fan with a smaller size can be selected to obtain the same air volume.

 

The main performance parameters of the cooling fan:

The main parameters of the cooling fan include flow, pressure, speed, power, etc...

 

The bearing system of the fan:

 

The bearing system of the fan generally recommends the use of ball bearings, because the longevity of the cooling fan usually depends on the reliability of its bearings, and the ball bearing system has been proven to have the characteristics of high efficiency and low heat generation. Ball bearings belong to rolling friction, rolling by metal balls, with a small contact surface and a small friction coefficient; while oil-bearing bearings have sliding friction and large contact surfaces. After long-term use, the oil will volatilize, the bearing is easy to wear, the friction coefficient is large, and the later noise is louder , Short life name. In addition to the large ventilation volume and high wind pressure of a good-quality fan, reliability is also very important. The type of bearing used by the fan appears to be very important here. High-speed fans always use ball bearings, while low-speed fans use low-cost oil bearings (Sleeve bearings). Oil-impregnated bearing fans only use one bearing; while ball-bearing fans all need two bearings, a single ball bearing is "1 Ball + 1 Sleeve", which still has an oil-impregnated bearing composition. More advanced than the single ball is the double ball bearing, that is, Two Balls. The life of oil-impregnated bearings is generally 10,000 hours, single ball bearings are 30,000 hours, and double ball bearings are more than 50,000 hours (when the ambient temperature is set below 25°C). The oil bearing used in the fan is made of copper-based powder sintered. The oil bearing needs to be added with lubricating oil to reduce the sliding friction. The lubricating oil is made of lithium-based grease and special engine oil. With long-term operation, the oil in the bearing will evaporate and become dry, the friction coefficient will increase, and the operation of the fan will be affected, abnormal noise may occur, and the rotation speed will be slow. The ball bearing replaces sliding friction with rolling friction, has a small friction coefficient and overcomes the shortcomings that the friction coefficient is easy to change, so it has strong running stability and a relatively longer lifespan.