Views: 0 Author: Site Editor Publish Time: 2022-07-04 Origin: Site
Centrifugal fan is a kind of driven fluid machinery, which depends on the input mechanical energy to increase the gas pressure and discharge the gas. Centrifugal fans are widely used in ventilation, dust removal and cooling of factories, mines, tunnels, cooling towers, vehicles, ships and buildings; Ventilation and induced draft of boilers and industrial furnaces; Cooling and ventilation in air conditioning equipment and household appliances; Drying and selection of grain; Wind source of wind tunnel and inflation and propulsion of hovercraft.
According to the principle of converting kinetic energy into potential energy, the centrifugal fan uses the high-speed rotating impeller to accelerate the gas, then decelerate and change the flow direction to convert kinetic energy into potential energy (pressure). In a single-stage centrifugal fan, the gas enters the impeller from the axial direction, changes into the radial direction when flowing through the impeller, and then enters the diffuser. In the diffuser, the gas changes the flow direction and the cross-sectional area of the pipe increases to decelerate the gas flow, which converts kinetic energy into pressure energy. The pressure increase mainly occurs in the impeller, followed by the diffusion process. In the multi-stage centrifugal fan, the reflux device is used to make the air flow enter the next impeller to produce higher pressure.
The working principle of centrifugal fan is basically the same as that of turbine compressor, because the gas flow rate is low and the pressure changes little. Generally, the change of gas specific volume does not need to be considered, that is, the gas is treated as an incompressible fluid.
Centrifugal fans can be made into two types: right-hand and left-hand. Face up from one side of the motor: the impeller rotates clockwise, which is called the right rotating fan; The impeller rotates counterclockwise, which is called left rotating fan.
Centrifugal fan is composed of casing, main shaft, impeller, bearing transmission mechanism and motor.
Casing: made of steel plate, it is solid and reliable, and can be divided into integral type and semi open type, which is convenient for maintenance.
Impeller: composed of blades, curved front disc and flat rear disc.
Rotor: static balance and dynamic balance should be done to ensure smooth rotation and good performance.
Transmission part: it is composed of main shaft, bearing box, rolling bearing and belt pulley (or coupling).
In 1862, guebel invented the centrifugal fan. Its impeller and casing are concentric circles, the casing is made of bricks, and the wooden impeller adopts backward straight blades, with an efficiency of only about 40%. It is mainly used for mine ventilation.
In 1880, people designed a worm shaped casing for mine ventilation and a centrifugal fan with backward curved blades, and the structure has been relatively perfect.
In 1892, France developed a cross flow fan; In 1898, the Irish designed the sirocco centrifugal fan with forward blades, which was widely used in various countries; In the 19th century, axial fan has been used in mine ventilation and blast in metallurgical industry, but its pressure is only 100 ~ 300 PA, and its efficiency is only 15 ~ 25%. It did not develop rapidly until the 1940s.
In 1935, Germany first used axial-flow isobaric fans to ventilate and induce air for boilers; In 1948, Denmark made axial flow fans with adjustable moving blades in operation; Rotary axial flow fan, meridian acceleration axial flow fan, diagonal flow fan and cross flow fan; In 2002, China's explosion-proof centrifugal fans were widely used in chemical, petroleum, machinery and other fields, and changlindong explosion-proof centrifugal fans have also been developed. Centrifugal fan is a commonly used auxiliary production equipment in stone processing enterprises. It is mainly used in ventilation and dust removal devices, such as cyclone dust collector and bag dust collector in stone cutting and grinding processes. Centrifugal fan is required to remove dust from the production site, so as to ensure the cleanness of the production environment and protect the physical and mental health of producers. Fan is a kind of equipment with high energy consumption, and the power resources that consume the fan account for a large proportion in stone processing. With the increasing shortage of energy in China and the promotion and application of high-yield and high-efficiency working faces, energy conservation and consumption reduction have become a common concern of stone production enterprises. Many stone production enterprises regard reducing the power consumption of the fan as an important work at present. In addition to improving the efficiency of the fan itself, it is most important to reasonably select the adjustment mode of the fan to reduce the power consumption of the fan, because the load of stone production changes from time to time with the needs of the process
Fans need to adjust the flow frequently according to the load of the main engine. At present, the energy-saving adjustment method of fans in stone processing enterprises is relatively old, and throttling adjustment is generally used. When throttling regulation is adopted, the flow of the fan is mainly regulated by regulating valve or throttling baffle. The throttling flow of the fan is large, and even throttling is more than 50% at low load. Due to throttling loss and deviation from the operation in high efficiency zone, the energy waste is very serious. If the speed of the fan is adjusted, it can not only eliminate the throttling loss, but also ensure that the fan always operates in the high-efficiency area, so it can greatly save electric energy. It can be said that adjusting the speed of the fan to operate the fan is an effective way to save energy, which reflects the new trend of the current production of building materials industry.
