Main components of centrifugal fan

The main components of centrifugal fan are similar to centrifugal pump. The gas is introduced from the air inlet box, and the air inlet volume is adjusted through the deflector, and then

It is led to the impeller suction port through the collector. The gas flowing out of the impeller is collected by the volute and led out after boosting by the diffuser. Not suitable for mining

Use multistage impeller. When the centrifugal fan transports gas, the general pressurization range is below 9.807kpa (1000mmh2o).

The following is only discussed in combination with the characteristics of the fan itself.

1) Impeller

Impeller is the main component of centrifugal pump fan to transfer energy. It is composed of front plate, rear plate, blade and hub (see Figure)

2-2）The blades are backward, radial and forward, as shown in Figure 4-21. The shape of backward blades is divided into wing type and forward type

Arc type, etc. Wing type blades have good aerodynamic characteristics, high efficiency, good strength and high rigidity, but the manufacturing process is complex

When transporting gas with high dust concentration, the blades are easy to wear. If the circular arc blade optimizes the aerodynamic performance,

Its efficiency will be close to that of wing blades. There is also a backward facing flat blade, which is simple to manufacture, but has poor flow characteristics and low efficiency.

Among the backward blades, wing shaped blades are mostly used for large centrifugal fans, while for medium and small centrifugal fans, wing shaped blades are used

Circular arc and flat plate blades are suitable.

(a) Forward blade impeller (b) multi blade forward blade impeller (c) circular arc impeller

(d) Radial arc impeller (E) radial straight blade impeller (f) wing impeller

There are three types of impeller front disc: straight front disc, conical front disc and arc front disc, as shown in Figure 4-22. Straight front disc system

It is simple to build, but the separation loss after air flow inlet is large, so the fan efficiency is low. The manufacturing process of curved front plate is complex, but the gas flows in

The separation loss behind the outlet is small, so the fan efficiency is high. The conical front disc is in between. The front plate of high-efficiency centrifugal fan adopts arc

Front disc.

2) Current collector

The fan is equipped with an inlet collector in front of the impeller. The function of the collector is to ensure that the air flow can be evenly distributed in the section of the impeller inlet,

Reach the speed value required by the inlet and enter the impeller with the minimum air loss. The collector forms are cylindrical and circular

Cone, arc, cone column, arc barrel and cone arc, etc., as shown in Figure 4-23. Arc, cone arc, good performance, large

The fan is used to improve the efficiency of the fan, and the high-efficiency fan basically adopts conical arc collector. The shape of the suction inlet shall be as consistent as possible

The flow condition of the air flow near the inlet of the hinge wheel to avoid leakage and loss.

Figure 4-23 collector form

(a) Cylindrical (b) conical (c) arc (d) conical cylindrical (E) arc cylindrical (f) conical arc

3) Casing

The function of the casing is to collect the air flow at the outlet of the impeller and lead it to the outlet of the fan. At the same time, part of the kinetic energy of the air flow is converted into pressure

Yes. Logarithmic spiral or Archimedean spiral is the best shell shape, with the highest efficiency. The casing section is rectangular and

And the width remains the same.

In order to effectively utilize the air flow at the outlet of the casing, the diffuser is still installed at the outlet of the casing

The air flow at the outlet of the casing is deflected to the rotation direction of the impeller by inertia, so the diffuser is generally expanded along the deflection direction

The divergence angle is usually 6 ° ~ 8 °, as shown in Figure 4-24.

There is a tongue like structure at the outlet of the centrifugal fan casing, which is generally called cochlear tongue (see Figure 4-24). Cochlear tongue can prevent gas from flowing in

Circulating flow in the casing. Generally, the efficiency and pressure of fans with volute tongue are higher than those without tongue.

The casing can be made of steel plate, plastic plate, FRP and other materials. Its cross section can be square or round, generally medium and low

Pressure fans are mostly square, while high-pressure fans are round. At present, the casing of the new fan developed and produced can rotate within a certain range

To meet the different needs of users for the direction of air outlet.

4) Intake box

There are three ways for airflow to enter the collector. One is free air intake; The other is the intake of air from the suction pipe, which requires to ensure

Sufficient length of axial suction duct; The other is the air inlet of the air inlet box. When the elbow needs to be set before the inlet of the air suction pipe, it is required to change the direction

An air inlet box is installed in front of the collector to replace the elbow air inlet, which can improve the air flow condition of the inlet air. See Fig. 4-25 for air inlet box

As shown in.

The shape and size of the air inlet box will affect the performance of the fan. In order to provide good air inlet conditions for the fan, the

Fluid mechanical pumps and fans by Liu Hongmin 3

There are certain requirements for its shape and size.

(1) The overflow section of the inlet box shall be gradually reduced, so that the air flow can be accelerated and then enter the collector. Bottom of intake box

It shall be flush with the air inlet to prevent eddy current caused by steps (see Figure 4-25).

(2) The ratio of the inlet cross-sectional area AI of the inlet box to the inlet cross-sectional area A0 of the impeller shall not be too small, which will make the fan

The pressure and efficiency decreased significantly, generally AI / A0 ≮ 1.5; Preferably, AI / A0 = 1.75 ~ 2.0.

Figure 4-24 volute figure 4-25 inlet box

(3) 90 ° is the best relative position between the air inlet box and the air outlet of the fan, that is, the air inlet box and the air outlet are orthogonal

When the two are 180 ° parallel, the air flow condition is the worst.

5) Population guide vane

A set of guide vanes (static guide vanes) with adjustable angle is set near the inlet in front of the impeller of centrifugal fan to control the fan

Flow regulation for operation. This guide vane is called Population guide vane or population deflector, or front guide vane. Common population guide vanes are axial

There are two kinds of deflector and simple deflector. The adjustment mode of population guide vane is widely used in centrifugal fan

The angle of the blade can expand the performance and application range of the fan and improve the economy of regulation.

From Changzhou Sunlight Blower Co., Ltd – maily products steel backward centrifugal fans ,plastic backward curved centrifugal fan , forward curved centrifugal fans ,inline duct fans and motors .