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How to select a cooling fan

Date:2018-11-08        Clicks:719

How to select a cooling fan

 

Classification of fans:

 

Cooling fans are generally classified into the following three categories:

 

Axial flow type: the exit direction of air flow is the same as that of the axis.

 

Centrifugal type: the air flow is thrown out along the blade by centrifugal force.

 

Mixed flow: having the above two air flow modes.


 

The principle of the cooling fan

 

Principle: the working principle of the fan is realized by energy conversion, that is: electric energy - electromagnetic energy - mechanical energy - kinetic energy. Its circuit principle is general divided into many forms, the circuit that USES is different, the performance of the fan can have difference.

 

Composition of axial flow fan:

 

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

 

Transfer rate:

 

Speed refers to the speed at which the fan rotates, usually measured by the number of turns per minute, or RPM. The rotating speed is related to the number of winding turns, diameter of wire, outer diameter and bottom diameter of fan blade wheel, blade shape and bearing used.

 

The value of rotating speed represents the size of air volume to a certain extent. When the rotating speed is higher, the noise and vibration will be increased correspondingly. Therefore, low-rotating fans should be used as far as possible when the air volume meets the heat dissipation requirements. General speed (take DC axial fan for example) : 2,510 fan 7000 ~ 12000rpm; 3010 fan 5000 ~ 9000rpm; 4010 fan 5000 ~ 7000rpm; Fan: 3,500 ~ 5000rpm; 6025 fan 2600 ~ 4500rpm; 7025 fan 2400 ~ 3600rpm; 8025 fan 2000 ~ 3500rpm; 9225 fan 1600 ~ 3100rpm; 12025 fan 1500 ~ 2500rpm; Fan: 12038, 2000 ~ 3200rpm.

 

The fan speed can be tested by the BIOS when starting the computer, or by other monitoring software installed on the motherboard; It can also be tested by the speed tester. Note: the first two methods must be a fan that supports speed measurement.


 

Bearing system of fan:

 

The bearing system of the fan is generally recommended to use the ball bearing as the service life of the fan usually depends on the reliability of the bearing. The ball bearing system has been proved to be of high efficiency and low heat generation. Ball bearing is rolling friction, rolling by metal beads, small contact surface, small friction coefficient; The oil-bearing is sliding friction, with large contact surface. After long-term use, the oil will evaporate. The bearing is easy to wear and wear. In addition to high ventilation rate and high air pressure, the reliability of the high-quality fan is also very important. Ball bearing is used for high speed fans while low speed fans use low cost oil bearing bearings. Oil bearing fan USES only one bearing; And the fan of Ball bearing needs two bearings, single Ball bearing, is "1 Ball + 1 Sleeve", still has the composition of oil bearing. More advanced than single ball bearings is the double ball bearing, or Two Balls. Oil bearing life in general is 10000 hours, the single ball bearing for 30000 hours, the double ball bearings for more than 50000 hours (ambient temperature are set under 25 ℃). The oil bearing used in the fan is made of copper base powder sintered. The oil bearing needs to be lubricated to reduce sliding friction. With the long-term operation, the oil in the bearing will become dry and volatile, the friction coefficient will increase, and the fan will be affected, which may lead to abnormal sound, slow speed or even no rotation. The ball bearing replaced the sliding friction by rolling friction, the friction coefficient is small and overcome the shortcoming of easy variation of friction coefficient, so the operation stability is strong and the life is relatively longer.

 

Dc fan specifications and characteristics

 

When you select a fan, the following knowledge will give you a useful reference, so that you really choose to match your own use of fan products.

 

I. selection of fan specifications:

 

1. Selection of the shape size of the fan frame:

 

1-1 times [length 25 x width 25 x thickness 10mm] : industry abbreviation 2510

 

1-2 solution [length 40 x width 40 x thickness 20mm] : industry abbreviation 4020

 

1-3 times [length 60 x width 60 x thickness 15mm] : the industry name is 6015

 

1-4 ab [length 80 x width 80 x thickness 25mm] : industry abbreviation 8025

 

1-5 waves [length 120 x width 120 x thickness 25mm] : industry abbreviation 12025

 

1-6 ab [length 120 x width 120 x thickness 38mm] : industry abbreviation 12038

 

1-6 composites [length 150 x width 150 x thickness 50mm] : industry abbreviation 12050

 

1-6 times [length 172 x width 150 x thickness 50mm] : industry abbreviation 17250

 

1-6 ab [180x length 180x width 180x thickness 60mm] : industry abbreviation 18060

 

1-6 times [length: 200 x width: 200 x thickness: 60mm] : industry abbreviation: 20060

 

1-6. [length: 250 * width: 250 * thickness: 90mm] : industry abbreviation: 25090, etc

 

The above fan shape dimensions have different screw hole spacing and screw hole diameter

 

As shown in the above description: fan installation dimensions for 60 * 60 * 15 mm (hereinafter referred to as "6015 fan), screw diameter was 4.4 mm Ф, pitch is 50.0 mm.

 

2. Selection of plastic material and color of fan frame and leaf:

 

2-1) fan box + blades: as the PBT material white plastic heat deformation temperature (230 ℃)

 

2-2) fan box + blades: as the PBT material black plastic heat deformation temperature (230 ℃)

 

+ blades: 2-3) fan box for PC material transparent plastic heat deformation temperature (150 ℃)

 

+ blades: 2-4) fan box for PC material with different toner appearance color plastic heat deformation temperature (120 ℃)

 

3. Selection of fan mechanical bearing system:

 

(3-1) dual-ball dust-proof structure

 

Dustproof construction design

 

Advantages:

 

A) the fan operates at a stable speed, and the fan's speed will not be changed in different locations

 

B) relatively long service life

 

C) easy to produce, process and assemble

 

Mixer shortcomings

 

A) high cost

 

3-2 mm single ball dust-proof structure

 

Advantages:

 

A) the fan operates at a stable speed, and the fan's speed will not be changed in different locations

 

B) moderate relative service life

 

Mixer shortcomings

 

A) the high cost

 

B) high processing difficulty and easy to produce heterophony in the process and use

 

3-3 sliding dust-proof hydraulic centering magnetic fan

 

Oil bearing center design

 

Return oil system design dustproof structure design solid magnet

 

Advantages:

 

A) high cost

 

B) moderate relative service life

 

C) interior and exterior dustproof design, magnetic center operation and internal oil return circulation system design, to extend fan service life

 

Mixer shortcomings

 

A) the processing difficulty accuracy requirements are quite high

 

3-4 sliding dust-proof hydraulic magnetic suspension fan

 

Dustproof construction design

 

Oil bearing

 

Axis of S420

 

Sealing structure

 

The oil return groove is not measured

 

Advantages:

 

A) moderate cost

 

B) moderate relative service life

 

C) interior and exterior dustproof design, internal oil return circulation system design, extend fan service life

 

Mixer shortcomings

 

A) the processing difficulty accuracy requirements are quite high

 

4. Selection of fan wire:

 

4-1) wire specification and model

 

Conventional dividing line:

 

Level of low UL1007 24 agw wire: 80 ℃, 300 v, the largest conductor impedance Ω 28.3 / KFT, 20 ℃

 

Level of low UL1007 agw wire 26:80 ℃, 300 v, the largest conductor impedance Ω 45.2 / KFT, 20 ℃

 

Level of low UL1095 28 agw wire: 80 ℃, 300 v, the largest conductor impedance Ω 6.64 / KFT, 20 ℃

 

Low level of 28 agw UL1571 wires: 80 ℃, 30 v, the largest conductor impedance Ω 6.64 / KFT, 20 ℃

 

Conventional and lines

 

Level of low UL2468 24 agw twisting wire: 80 ℃, 300 v, the largest conductor impedance Ω 28.3 / KFT, 20 ℃

 

Level of low UL2468 24 agw twisting wire: 80 ℃, 300 v, the largest conductor impedance Ω 45.2 / KFT, 20 ℃

 

Level of low UL1095 28 agw twisting wire: 80 ℃, 300 v, the largest conductor impedance Ω 6.64 / KFT, 20 ℃

 

4-2) common terminal specifications and models

 

JST 2.5(2P) JST 2.5(3P) 2510(2P) 2510(3P) JST 2.0(2P) JST 2.0(3P)

 

Molex1.25(2P) Molex1.25(3P) Molex5264(3P) dupont 2.54(3P) SMH250(2P) AMP mat-100

 

4-3) wire length representation

 

Wire length solder length

 

Traverse length algorithm for terminal fans and traverse length algorithm for terminal fans

 

5. Air supply mode, axial flow fan and centrifugal fan

 

Axial fan (5-1) : the most extensive form is using axial fans (the most common type of fans) to draw down the air. If the axial fan is turned in the opposite direction, it becomes an updraft, which is used in certain types of radiators. The difference between the two modes of air supply lies in the difference of air flow form. The turbulent flow is generated when the air is blown, and the wind pressure is high, but it is vulnerable to the loss of resistance. When the wind is blowing, there is laminar flow, the wind pressure is small but the air flow

 

Stability. In theory, turbulence is much more efficient than laminar flow, which makes it a mainstream design. Axial flow fan

 

Although widely used, there are inherent defects. The axial fan is blocked by the position of the motor, so the air cannot flow smoothly

 

In the middle of the blast zone, this is called the dead zone.

 

Positive turn [counter-clockwise, the outgoing direction of the fan is the positive back direction]

 

Reversal [clockwise direction, out direction of fan outlet direction]

 

Centrifugal fans (5-2 centrifugal fans) [Blower] : centrifugal fans, which are completely different from axial fans, are also gradually being used in CPU cooling, often referred to as "turbofans" by computer users. The advantage of this fan is that it solves the "dead zone" problem well. The centrifugal fan differs from the traditional fan in that its blade rotation is carried out in a vertical plane and the air inlet is located at the side of the fan. The air flow received by the bottom of the radiator is evenly distributed.

 

There is no obstacle in the direction of the centrifugal fan's blast, so the same airflow is available in all positions. And its wind pressure and air volume

 

The adjustment range is also larger and the speed control effect is better. Negative impact noise.

 

Turn [counterclockwise, out of the air outlet]

 

[clockwise direction, outlet into the wind]

 

Ii. Basic items of fan electrical characteristics:

 

1) selected according to the rated voltage and voltage range of the fan

 

1-1 ac DC5V [range of operating voltage: 4.5v ~ 5.5v]

 

1 -- 2 abs DC12V [range of operating voltage: 10.2v ~ 13.8v]

 

1-3 ac DC24V [range of operating voltage: 20.4V ~ 27.6V]

 

1-4 ac DC48V [range of operating voltage: 43V ~ 52V]

 

1-5) specification of some special rated voltage and voltage range requirements

 

2) fan starting voltage requirements

 

Definition of starting voltage: the voltage that enables the fan to operate normally at the lowest voltage. The smaller the starting voltage means that the fan's static friction coefficient is small, and the fan's running and rotating speed are more smooth and stable. It is necessary to select a good fan.

 

Rated current requirement of the grinding fan

 

Current when the fan is in stable operation under rated voltage [current indication symbol: I, unit :A(ampere),1A = 1000mA]. The smaller the current, the better the heat dissipation efficiency, the less energy it will consume and the longer the fan will last.

 

4. Rated speed of the driven fan

 

(represents the normal maximum speed of the fan under the condition of safe use)

 

4-2) high speed

 

4-3) in the speed

 

4-4) low speed

 

Ultra-low speed (represents the minimum speed at which the fan can continue to operate normally under rated voltage)

 

5. Function requirements for automatic restart of the fan

 

The lock function for the fan rotor, fan current moment from large to small (almost as zero A) locking, let go of the rotor, the rotor in A stop state, A few seconds (the length of the stop time by IC conventional design or special needs for adjusting itself) from IC internal release can guide voltage will automatically after the fan has resumed work, fan rotor started from state stopped functioning.

 

This function is mainly to prevent the fan rotor from being stuck or the fan from dead Angle due to external factors during installation and use, and the fan will burn out due to the influence of high current.

 

6. Noise requirements for fans [dB dB(A)]

 

Fan noise is the most concerned by users. Under the precondition of heat dissipation, the smaller the noise requirement, the better. Fan noise is related to friction and air flow. The higher the fan speed, the greater the air volume, the noise will be greater, in addition, the vibration of the fan itself is also a factor that cannot be ignored. Of course, high-quality fans will have little vibration of their own, but the first two are difficult to overcome. To solve this problem, we can try to use a larger fan. The working noise of large fan at low speed should be less than that of small fan at high speed when the air volume is the same. Another factor that we tend to overlook is the bearing of the fan.

 

As the fan rotates at high speed, friction between the shaft and the bearing is a major source of fan noise. The noise test standard is measured by the distance between the Microphone and Fan 1M (as shown in the figure below). Special requirements will shorten the distance between the Microphone and Fan.  

 

Air volume & air pressure requirements for ventilating fan

 

Fan air volume and air pressure is to determine the cooling efficiency of the main factors, often decided after fan shaped specifications, the characteristics of the fan the key requirement is that air volume and air pressure, is by no means the fan speed, often people will misunderstand this emphasis, began to use A manufacturer of fan speed is 2400 RPM, as long as the fan manufacturer B for 2400 RPM, is completely wrong to do so. If A manufacturer 4028 fan speed is 8000RPM, air volume is 3