1. In principle
Principle of centrifugal fan: the airflow flows axially into the rotating blade passage, is thrown to the outer edge of the impeller under the action of centrifugal force, and is discharged from the air outlet.
2. Principle of axial flow fan: The gas enters the rotating blade channel axially and is pressurized, and then discharges axially from the other side.
2. Structure
a. Centrifugal fans are generally composed of impellers, casings, current collectors, motors and transmission parts (such as spindles, pulleys, bearings, V-belts, etc.). The impeller consists of a disk, blades (the number of blades is generally 8-16), a wheel cover, and a shaft disk. The casing is composed of a volute plate, a side plate and an outrigger. Centrifugal fans can adopt forward or backward leaning blades, which can meet the requirements of air volume and pressure more widely. In addition, the cabinet can be muffled, which has obvious advantages in terms of noise indicators. The motor and the fan are generally connected by a shaft.
b. Axial fans are generally composed of an impeller, a casing, a current collector and a motor. The impeller is composed of blades and a hub, and the casing is composed of a fan tube, a frame plate and a bracket. The blade diameter of an axial fan is limited to the diameter of the casing. The motor is generally in the fan.
3. Air volume and wind pressure
a. Centrifugal fans have high pressure coefficient and relatively low flow coefficient. According to the pressure, they are divided into high pressure (15000～3000Pa), medium pressure (3000～1000Pa), and low pressure (<1000Pa).
b. The axial flow fan has the characteristics of low pressure and large flow. According to the pressure, it is divided into high pressure (500～5000Pa) and low pressure (<500Pa). Low pressure is mainly used for ventilation in general places.
4. Installation
Centrifugal fans are often installed at the inlet and outlet of air conditioning units, boiler drums, induced draft fans, etc. The installation is more complicated, and the installation of axial fans is often in the middle of the duct or at the front of the duct outlet.
