Centrifugal fan

Centrifugal ventilation fan mainly consists of impeller, casing, coupling, and shaft. The impeller is the main working component that generates wind pressure and transmits energy; The casing is mainly used to introduce and exhaust gas, while converting some of the kinetic energy of the gas into pressure energy; Couplings are used to connect motors and fans, transmitting torque; Install and fix the impeller on the shaft, and connect it to the motor through a coupling.

Principle of centrifugal fan

When the gas between the blades of a centrifugal fan rotates, it gains kinetic energy (dynamic pressure head) under the action of centrifugal force and is discharged from the periphery of the impeller. Through the guidance of the volute shaped casing, it flows towards the outlet of the fan, forming negative pressure at the impeller, allowing external airflow to flow in for replenishment, thereby enabling the fan to discharge gas.

The electric motor transmits power to the fan impeller through the shaft, and the impeller rotates to transfer energy to the air. Under the action of rotation, the air generates centrifugal force, and the air spreads around the blades of the fan impeller. At this time, the larger the fan impeller, the greater the energy received by the air, that is, the greater the pressure head (wind pressure) of the fan. If the large impeller is cut smaller, it will not affect the air flow, only reduce the air pressure.

Centrifugal fans are mainly composed of impellers and casings. The impellers of small fans are directly mounted on the electric motor, while the impellers of large fans are connected to the electric motor through couplings or pulleys. Centrifugal fans generally have single-sided air intake and use single-stage impellers; Double suction centrifugal fans with high flow rates can be equipped with dual sided air intake and two back-to-back impellers.

The impeller is the main component of a ventilation fan, and its geometric shape, size, number of blades, and manufacturing accuracy have a significant impact on performance. The impeller must undergo static balance or dynamic balance correction before the ventilation fan can rotate smoothly. According to the different outlet directions of the blades, impellers are divided into three types: forward, radial, and backward. The top of the blades of the forward facing impeller tilts towards the direction of rotation of the impeller; The top of the blades of a radial impeller is radially oriented and can be divided into straight blade and curved blade types; The top of the blades of the backward impeller tilts in the opposite direction to the rotation of the impeller.

The pressure generated by the forward impeller is high, and the required impeller diameter is small at flow rate and speed, but the efficiency is generally low; The backward facing impeller produces less pressure, requires a larger impeller diameter, and generally has higher efficiency; The radial impeller is between the two. The blade profile is simple with straight blades and complex with wing shaped blades.

In order to achieve a suitable velocity distribution on the surface of the blade, curved blades, such as equal thickness circular arc blades, are generally used. Impellers usually have cover plates to increase the strength of the impeller and reduce gas leakage between the blades and the casing. The connection between the blades and the cover plate is achieved through welding or riveting. The weight of the welded impeller is relatively light, and the flow channel is smooth. The impellers of low and medium pressure small centrifugal fans are also made of aluminum alloy casting.