When the centrifugal fan works, the power machine drives the impeller to rotate in the volute casing, and the air is sucked in from the center of the impeller through the air suction opening. As a result of the dynamic action of the blade on the gas, the gas pressure and velocity are increased, and the centrifugal force is thrown along the blade path toward the casing and discharged from the exhaust port. The flow of gas in the impeller is mainly in the radial plane, so it is also called radial flow fan.
The centrifugal fan is mainly composed of an impeller and a casing, the impeller of the small fan is directly arranged on the motor, and the large ventilator is connected with the motor through a shaft coupling or a belt pulley. Centrifugal fan is usually a single inlet, with a single-stage impeller; large flow can be bilateral intake, with two back to back impeller, also known as double suction centrifugal fan.
Impeller is the main component of fan. Its geometry, size, number of blades and manufacturing accuracy have great influence on its performance. The impeller is balanced by static or dynamic balance to ensure the smooth rotation of the ventilator. According to the direction of the blade exit, the impeller is divided into three types: forward, radial and backward. Prior to the top of the impeller blade to the impeller rotation direction tilt; blade tip radial impeller is radial, and straight blade and curved blade; backward at the top of the blade impeller to reverse rotation of the impeller tilt.
The maximum pressure generated by the impeller, flow and speed in certain, the required minimum impeller diameter, but the efficiency is low; to the impeller instead, the pressure generated by the minimum required impeller diameter, and the efficiency is generally higher; somewhere between the radial impeller. The shape of the blade is straight, the blade is the simplest, and the airfoil blade is the most complicated.
In order to make the blade surface have a suitable velocity distribution, curved blade is adopted, such as equal thickness circular blade. The impeller usually has a cover plate to increase the strength of the impeller and reduce the leakage of gas between the blade and the housing. The connection between the blade and the cover plate is welded or riveted. The welding impeller is light in weight and smooth in the runner. The impeller of low and medium pressure centrifugal fan is also made of aluminium alloy.
When the axial fan works, the power driven impeller rotates in the cylindrical casing, the gas enters from the flow collector and obtains energy through the impeller to increase the pressure and speed, and then exhaust along the axial direction. Axial fan arrangement has vertical, horizontal and inclined three, small impeller diameter of only about 100 millimeters, large can reach more than 20 meters.
Small low pressure axial fan impeller, casing and other components of the collector, usually installed in the wall of a building or a ceiling; large high pressure axial flow fan by the collector, impeller, casing, cylinder body, streamline diffusion and transmission parts. The blades are evenly arranged on the wheel hub, and the number is generally 2~24. The more the blade, the higher the wind pressure; the blade installation angle is generally 10 degrees to 45 degrees; the greater the installation angle, the greater the air volume and wind pressure. Most of the main parts of axial fans are welded or riveted by steel plates.
The main difference between centrifugal fans and axial fans is that:
1. The centrifugal fan changes the flow direction of the medium in the air duct, while the axial fan does not change the flow direction of the medium in the air duct;
2, the former installation is more complex;
3, the former motor and fan are generally connected through the shaft, the latter motor generally in the fan;
4, the former is often installed in the air conditioning unit inlet and outlet, boiler drum, fan, and so on. The latter is usually installed in the middle of the air duct or the front end of the air duct.