Types of fans and how they work

A fan is a mechanical machine that relies on input mechanical energy to increase gas pressure and direct gas flow. It is a driven fluid machine. The working principle of the fan is basically the same as that of the turbo compressor, except that the gas flow rate is low and the pressure does not change much. Generally, the change of the gas specific volume is not considered, that is, the gas is treated as an incompressible fluid. The fan is divided into an axial flow fan, a centrifugal fan and a diagonal flow (mixed flow) fan according to the flow direction of the airflow after entering the impeller.

Centrifugal fan

The airflow enters the rotating vane passage, and under centrifugal force the gas is compressed and flows in the radial direction.

The centrifugal fan is based on the principle that kinetic energy is converted into potential energy. The high-speed rotating impeller accelerates the gas, then decelerates and changes the flow direction, so that the kinetic energy is converted into potential energy (pressure). In a single-stage centrifugal fan, gas enters the impeller from the axial direction, the gas changes to radial direction as it flows through the impeller, and then enters the diffuser. In the diffuser, the gas changes the flow direction to cause deceleration, which converts kinetic energy into pressure energy. The increase in pressure mainly occurs in the impeller, followed by the expansion process. In a multistage centrifugal fan, a return flow is used to direct the gas flow to the next impeller, resulting in higher pressure. Suzhou Dingyu is one of the professional centrifugal fan manufacturers.

2. Axial fan

After the airflow enters the fan impeller axially, the fan flows in the axial direction in the flow path of the rotating blade. Compared with the centrifugal fan, the axial flow fan has the characteristics of large flow, small volume and low pressure head. It should be used when there are dust and corrosive gas.

When the impeller rotates, the gas enters the impeller axially from the air inlet, is pushed by the blades on the impeller, and the energy of the gas rises, and then flows into the vane. The vanes change the deflected airflow into an axial flow, and at the same time introduce the gas into the diffuser tube, further convert the gas kinetic energy into pressure energy, and finally introduce the working line.

3. Diagonal flow (mixed flow) fan

In the impeller of the fan, the direction of the airflow is between the axial flow and flows along the cone, so it can be called a diagonal flow (mixed flow) fan. This type of fan has a higher pressure coefficient than an axial flow fan, and the flow coefficient is higher than that of a centrifugal fan.

When the impeller rotates, the gas enters the impeller axially from the air inlet, and the beret beam is pushed by the blades on the impeller to raise the energy of the gas and then flow into the vane. The vanes change the deflected airflow into an axial flow, and at the same time introduce the gas into the diffuser tube, further convert the gas kinetic energy into pressure energy, and finally introduce the working line.