What is a Centrifugal Fan?

Figure 1: A centrifugal fan.

When the fan works, the air flow enters the blade from the axial direction of the fan. Then, it will rotate with the impeller driven by the impeller. At the same time, the air flow increases energy under the action of inertia and leaves the impeller along the radius direction. Then it work by the centrifugal force generated. The fan working in this way is called centrifugal fan.

1. Structure

Centrifugal fan is composed of casing, main shaft, impeller, bearing transmission mechanism and motor.

Casing: made of steel plate, solid and reliable, can be divided into integral type and semi open type, which is convenient for maintenance.

Impeller: composed of blades, curved front disc and flat rear disc.

Rotor: it shall be tested for static balance and dynamic balance to ensure stable rotation and good performance.

Transmission part: it is composed of main shaft, bearing box, rolling bearing and pulley (or coupling).

Figure 2: The structure of a centrifugal fan.

2. Classification

Centrifugal fans can be divided into low-pressure centrifugal fans, medium-pressure centrifugal fans (air pressure 980-2942pa) and high-pressure centrifugal fans (air pressure 2942-14710pa).

According to different purposes, it can be divided into:

1.1 General Centrifugal Fan

General centrifugal fan is used for ventilation to buildings and air supply to industrial furnaces. The dust centrifugal fan is used to discharge the air containing dust such as grinding wheel, abrasive particle and sawdust.It can also be used for shaving and pneumatic conveying.

1.2 Pulverized Coal Centrifugal Fan

Pulverized coal centrifugal fan is used for conveying pulverized coal in thermal power plant.

1.3 Boiler Centrifugal Fan

Figure 3: Boiler centrifugal fans.

The boiler centrifugal fan is used for air supply and smoke exhaust of thermal power station and other industrial steam boilers. One kind of air supply is called ventilator and the other kind of smoke exhaust is called induced draft fan.

1.4 Explosion Proof Centrifugal Fan

Explosion proof centrifugal fan is used to discharge flammable and explosive gases. Most impeller materials of this kind of fan are gold containing aluminum.

1.5 High Temperature Centrifugal Fan

High temperature centrifugal fan is used to discharge gas with temperature above 250C ° and it is used for gold treatment, power station, chemical industry, etc.

3. How Centrifugal Fan Works

Figure 4: Working diagram of centrifugal fan.

According to the principle of converting kinetic energy into potential energy, the centrifugal fan uses the high-speed rotating impeller to accelerate the gas, then decelerate and change the flow direction to convert kinetic energy into potential energy (pressure).

In a single-stage centrifugal fan, the gas enters the impeller from the axial direction and changes into the radial direction when flowing through the impeller. Then it enters the diffuser. In the diffuser, the gas changes the flow direction and the cross-sectional area of the pipe increases to slow down the gas flow. This deceleration converts kinetic energy into pressure energy. The pressure increase mainly occurs in the impeller followed by the diffusion process.

In the multistage centrifugal fan, the reflux device is used to make the air flow enter the next impeller to produce higher pressure.

4. Function

Centrifugal fan is a kind of driven fluid machinery, which depends on the input mechanical energy to increase the gas pressure and discharge the gas. Centrifugal fans are widely used in ventilation, dust removal and cooling of factories, mines, tunnels, cooling towers, vehicles, ships and buildings.It is also used for ventilation and induced draft of boilers and industrial furnaces; cooling and ventilation in air conditioning equipment and household electrical appliances; drying and selection of grain; manufacture of artificial air source and inflation and propulsion of hovercraft.

People make use of the working principle of centrifugal fan and successfully extend it to everywhere. With the development of social economy and the progress of human civilization, centrifugal fan will play more and more roles in production and life. And it will become an indispensable mechanical equipment in human society.

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