Working Principle of Centrifugal Fan

Working Principle of Centrifugal Fan:

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

Centrifugal fans have great advantages in application, which can improve the ratio of gas pressure and flow. Centrifugal fans are usually used in air conditioning, ventilation and air conditioning systems, ventilation systems, etc. In addition, it is also widely used in mechanical industry, chemical metallurgy, petrochemical industry, air separation, food processing and other fields.

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Centrifugal fans are generally divided into single-stage single suction centrifugal structure and multi-stage centrifugal structure.

In a single-stage centrifugal fan, the gas enters the impeller from the axial direction, changes to the radial direction when it flows through the impeller, and then enters the diffuser.(Its characteristics are: high gas velocity, large pressure, small flow; simple structure, easy processing; large pressure and flow; easy installation and use.) In the diffuser, the gas changes the flow direction and causes deceleration, which converts kinetic energy into pressure energy. The pressure increase mainly occurs in the impeller, and secondly in the diffusion process.

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In a multistage centrifugal fan, a reflux device is used to make the air flow enter the next impeller to generate higher pressure. In the fan, the high-speed rotating impeller continuously accelerates the gas. When the air flows through the impeller, it decelerates and changes direction, reducing the gas speed; Use a reflux device to make part of the air enter the next impeller, so that part of the air flow enters the previous impeller. When the air flow returns from the centrifugal compressor, the air is compressed in the reflux. In order to further increase the flow range and improve the pressure, a pressure compensation device (or pressure relief device) can be set at the fan inlet to make the pressure increase faster than the speed of gas passing through the fan or the pressurization coefficient.

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In order to achieve these purposes, the main technical measures are as follows: first, increase the flow rate by increasing the pressure drop of the gas at the fan inlet; Second, use the pumping function of the compressor to increase the load; Third, use the supercharging effect of the air compressor to improve the speed.

Function: The working principle of the centrifugal fan is basically the same as that of the turbine compressor. Because the gas flow rate is low and the pressure changes little, it is generally unnecessary to consider the change of the gas specific volume, that is, treat the gas as an incompressible fluid. However, for large centrifugal fans, due to the high rotor speed and large impeller diameter, the change of gas specific volume must be considered. In general, the centrifugal fan can be regarded as a kind of centrifugal compressor.

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The centrifugal fan can be made into two types: right rotation and left rotation:

Right rotating centrifugal fan: when the impeller rotates, the inner surface of the impeller is not in direct contact with the gas, but there is an air flow ring composed of the impeller edge on its circumference. The air flow rotates around a central axis in this air ring, and this central axis is the radial movement of the rotation on the other edge of the circumference.

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Left rotating centrifugal fan: it realizes the rotation and flow of gas by changing the direction of the blade; When the gas flows through the blade, eddy currents are formed on its circumference.

From the perspective of efficiency and pressure, the right cyclone has higher efficiency and pressure than the left one. However, due to the fact that the air flow on the right cyclone blade is relatively gentle, the rotation stability is good, and the impeller outlet does not need to consider the change of gas specific volume when the wind pressure increases, it is not suitable for use as a large centrifugal fan.

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The main components of the centrifugal fan are:

① The impeller is a circular thin shell structure, which uses gas to push the impeller to make the fan rotate at high speed and generate centrifugal force, so that the airflow can obtain great kinetic energy.

② The casing is a component connecting the motor and the fan as a whole, generally made of cast steel or cast iron.

③ Motor: generally composed of synchronous motor or asynchronous motor with good high-speed performance and low price (such as AC synchronous motor).

④ Transmission device: connect the high-speed rotating impeller with the transmission shaft, and use belt transmission or chain transmission.

Kyushu Pratt&Whitney Group

Hotline/WeChat: 13676219124

Introduction: Jiuzhou Pratt&Whitney Group, founded in 1996 and headquartered in Nanhai District, Foshan City, is a high-tech enterprise integrating R&D, production, sales and service.

Its main products include: industrial fans, environmental friendly air conditioners (air coolers), atomizing cooling machines, fresh air systems, motors, etc.

Now it has become the largest general machinery production base with the most complete product series in the same industry in China.