1. Centrifugal fan

Centrifugal blower fan is based on the principle of converting kinetic energy into potential energy, using a high speed rotating impeller to accelerate the gas, then decelerate and change the flow direction, so that the kinetic energy is 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 the gas flows through the impeller, and then enters the diffuser. In the diffuser, the gas changes the direction of flow to cause deceleration, which converts kinetic energy into pressure energy. The increase in pressure mainly occurs in the impeller, by the expansion process.

Centrifugal fan is essentially a variable flow and constant pressure device. When the speed is constant, the pressure-flow theoretical curve of the centrifugal fan should be a straight line. Due to internal losses, the actual characteristic curve is curved. The pressure generated in the centrifugal fan is greatly affected by changes in the temperature or density of the intake air. For a given intake air volume, the highest intake air temperature (lowest air density) produces the lowest pressure. For a given pressure and flow characteristic curve, there is a power and flow characteristic curve. When the blower is running at a constant speed, for a given flow rate, the required power increases as the intake air temperature decreases.

2. Axial fan

Axial flow fans are airflow in the same direction as the axis of the blades. For example, electric fans and air conditioner fans are fans operating in axial flow. It is called "axial flow" because the gas flows parallel to the fan axis. Axial fans are usually used in occasions with higher flow requirements and lower pressure requirements. The axial fan fixes the position and moves the air.

The cross section of an axial fan is generally a wing section. The blade can be fixed in position, or it can rotate around its longitudinal axis. The angle between the blades and the airflow or the distance between the blades may not be adjustable or adjustable. Changing the blade angle or pitch is one of the main advantages of axial fans. A small blade pitch angle produces a lower flow rate, while increasing the pitch can produce a higher flow rate.

3. Cross flow fan

Cross flow fan, the impeller is multi-blade, long cylindrical, with forward multi-wing blades. When the impeller rotates, the airflow enters the blade cascade from the open part of the impeller, passes through the interior of the impeller, and is discharged into the volute from the other side of the cascade to form a working airflow. The airflow in the impeller is very complicated, the air velocity field is unstable, and there is a vortex in the impeller, the center is located near the volute tongue. The existence of the vortex causes a circulating flow at the output end of the impeller. Outside the vortex, the airflow streamline in the impeller is arc-shaped. Therefore, the flow velocity of each point on the outer circumference of the impeller is not consistent. The closer to the vortex center, the higher the speed, and the closer to the volute, the lower the speed.

The air velocity and pressure at the air outlet of the fan are not uniform, so the flow coefficient and pressure coefficient of the fan are average values. The position of the vortex has a greater impact on the performance of the cross-flow fan. The center of the vortex is close to the inner circumference of the impeller and close to the volute tongue. The degree of stability increases.