With the development of science and technology, the production of fans is more refined, which is therefore divided into a variety of different types.
1, centrifugal fan
When the centrifugal fan works, the power machine (mainly the motor) drives the impeller to rotate in the cochle-shaped housing, and the air is sucked from the center of the impeller through the intake port. Due to the dynamic effect of the blade on the gas, the pressure and speed of the gas are increased, and under the action of centrifugal force, the gas is thrown along the blade path to the housing and discharged from the exhaust port. Because the flow of gas in the impeller is mainly in the radial plane, it is also called runoff fan.
The centrifugal fan is mainly composed of an impeller and a housing. The impeller of the small fan is directly installed on the motor. The medium and large fan are connected with the motor through a coupling or pulley. The centrifugal fan is generally unilateral intake, with a single stage impeller; Large flow can be double-sided intake, with two back-to-back impellers, also known as double-suction centrifugal fan.
The impeller is the main component of the fan, and its geometry, size, number of blades and manufacturing accuracy have great influence on the performance. The impeller can be corrected by static balance and dynamic balance to ensure the smooth rotation of the fan. According to the different direction of the blade outlet, the impeller is divided into forward, radial and backward three types. The top of the blade of the forward impeller is inclined to the rotating direction of the impeller; The top of the blade of the radial impeller is radial, and it is divided into straight blade type and curved blade type. The tip of the blade of a backward impeller is tilted against the rotation of the impeller.
2, pipe fan
The pressure generated by the forward impeller is the largest, and the required impeller diameter is the smallest when the flow rate and the number of revolutions are constant, but the efficiency is generally low. On the contrary, the backward impeller produces the least pressure, the required impeller diameter is the largest, and the efficiency is generally higher; The radial impeller is somewhere in between. The blade profile is the simplest in straight blade and the most complicated in airfoil blade.
In order to have a suitable velocity distribution on the blade surface, curvilinear blades are generally used, such as arc blades of equal thickness. The impeller usually has a cover plate to increase the strength of the impeller and reduce gas leakage between the blade and the housing. The connection between the blade and the cover plate is welded or riveted. The weight of the welded impeller is light and the flow path is smooth. The impeller of low and medium pressure small centrifugal fan is also cast with aluminum alloy.
3, axial flow fan
When the axial flow fan works, the power engine drives the impeller to rotate in the cylindrical shell, the gas enters from the collector, obtains energy through the impeller, increases the pressure and speed, and then exhausts along the axis. Axial flow fan layout has three kinds of vertical, horizontal and inclined, small impeller diameter is only about 100 mm, large up to 20 meters or more.
4, axial flow fan
The small low-pressure axial flow fan is composed of an impeller, a shell and a flow collector, and is usually installed on the wall or ceiling of a building. The large high pressure axial flow fan is composed of a flow collector, an impeller, a streamline body, a casing, a diffusion cylinder and a transmission component. The blades are evenly arranged on the hub, and the number is generally 2 to 24. The more blades, the higher the wind pressure; Blade installation Angle is generally 10° ~ 45°, the larger the installation Angle, the greater the air volume and wind pressure. The main parts of the axial flow fan are mostly welded or riveted by steel plates.
5, inclined flow fan
Oblique flow fan is also known as mixed flow fan, in this type of fan, the gas enters the impeller at an Angle to the axis, obtains energy in the blade channel, and flows out in the inclined direction. The shape of the impeller and the housing of the fan is conical. This fan has the characteristics of both centrifugal and axial flow, and the flow range and efficiency are between the two.
6, cross flow fan
A cross-flow fan is a small high pressure centrifugal fan with a forward multi-blade impeller. The gas enters the impeller from one side of the outer edge of the rotor, and then exits from the other side through the inside of the impeller, and the gas is twice acted on by the force of the blade in the impeller. Under the conditions of the same performance, its size is small and the speed is low.
Compared with other types of low-speed fans, cross-flow fans have higher efficiency. Its axial width can be arbitrarily selected without affecting the flow state of the gas, and the gas still maintains a uniform flow across the width of the rotor. Its narrow and long exit section is suitable for installation in a variety of flat shaped equipment for cooling or ventilation.
The performance parameters of the fan mainly include flow, pressure, power, efficiency and speed. In addition, the size of noise and vibration is also the main technical indicators of the fan. Flow rate, also known as air volume, is expressed by the volume of gas flowing through the fan in a unit time; Pressure, also known as wind pressure, refers to the pressure increase value of gas in the fan, which is divided into static pressure, dynamic pressure and total pressure. Power refers to the input power of the fan, that is, the shaft power. The ratio of effective fan power to shaft power is called efficiency. The full pressure efficiency of the fan can reach 90%.
The future development of the ventilator will further improve the aerodynamic efficiency, device efficiency and use efficiency of the ventilator to reduce power consumption; The large centrifugal fan is replaced by the axial fan with adjustable moving blade. Reduce fan noise; Improve the wear resistance of the impeller and casing of smoke and dust exhaust fan; Achieve variable speed adjustment and automatic adjustment.