Working principle of centrifugal fan
According to the principle of converting kinetic energy into potential energy, centrifugal fan uses the high-speed rotating impeller to accelerate the gas, then decelerate and change the flow direction, so that the kinetic energy can be converted into potential energy (pressure). In a single-stage centrifugal fan, the gas enters the impeller from the axial direction, changes to the radial direction when flowing through the impeller, and then enters the diffuser. In the diffuser, the gas changes the flow direction and the increase of the cross-section area of the pipe slows down the gas flow, which converts the kinetic energy into the pressure energy. The increase of pressure mainly occurs in the impeller, followed by the expansion process. In the multistage centrifugal fan, the air flow is sent into the next impeller with a reflux device to produce higher pressure.
1、 Fan function
The working principle of centrifugal fan is basically the same as that of turbine compressor, because the gas flow rate is low and the pressure changes little, it is generally not necessary to consider the change of gas specific volume, that is, the gas is treated as an incompressible fluid.
Centrifugal fans can be made into two types: right-hand and left-hand. Face from one side of the motor: the impeller rotates clockwise, which is called the right rotating fan; the impeller rotates counterclockwise, which is called the left rotating fan.
2、 Fan structure
Centrifugal fan is composed of casing, main shaft, impeller, bearing transmission mechanism and motor.
1. Shell: made of steel plate, it can be divided into integral type and semi open type, and semi open type is convenient for maintenance.
2. Impeller: composed of blade, curved front plate and flat back plate.
3. Rotor: static balance and dynamic balance shall be done to ensure smooth rotation and good performance.
4. Transmission part: composed of main shaft, bearing box, rolling bearing and pulley (or coupling)
3、 Performance characteristics
Centrifugal fan is a kind of variable flow and constant pressure device. When the rotating speed is fixed, the theoretical curve of pressure flow of centrifugal fan should be a straight line. Because of the internal loss, the actual characteristic curve is curved. The pressure produced in the centrifugal fan is greatly affected by the change of inlet air temperature or density. For a given amount of air intake, the pressure generated at the highest air intake temperature (the lowest air density) is the lowest. For a given pressure and flow characteristic curve, there is a power and flow characteristic curve. When the blower operates at a constant speed, for a given flow, the required power increases with the decrease of air intake temperature
