Since ancient times, people have equipped their homes with the simplest natural ventilation systems, but time passed, and progress did not stand still. With the appearance of the first factories and factories, there was a need for forced ventilation. Different began to appear ventilation devices, some of them have survived to this day. One such device is a centrifugal fan.
Content
- Purpose and application
- Device
- Varieties of the device
- Operating principle
Purpose and application
Centrifugal fans are designed for gas movement, they are used in those places where a significant increase or decrease in pressure is not required (the maximum compression ratio for fans is 1.15). For example, in cooling systems for household appliances - to remove hot air from the radiator, in heating appliances - for blowing heating elements, in smoke removal and ventilation systems, at enterprises - for pumping gases, etc. etc.
Device
Centrifugal fans, commonly called snails due to their similar appearance, consist of the following parts: a spiral casing,
impeller with blades installed on it, having bends forward or backward at the ends, a frame, and a drive (electric or pneumatic).Sectional view:
The arrows indicate the movement of the gas flow during the operation of the fan unit.
The direction in which the bends on the blades are directed is determined by the purpose of a particular fan. Backward-curved blades provide 20% higher efficiency and the ability to operate normally during overloads by gas consumption. Units with forward curved blades have the advantages of lower noise levels due to lower rotation speed, and compactness, due to the smaller size of the impeller and, accordingly housing.
The frame contains bearings for the motor and impeller shafts. Fan units are usually equipped with roller bearings, filled with oil. On those models that are operated at high temperatures, to avoid overheating, the bearings are equipped with a water cooling system.
Inlet and outlet dampers can also be installed in the fan to control the gas flows inside it.
Varieties of the device
There are many different types of fan units available today. Each is designed for certain operating conditions, which are different everywhere, so there are no universal solutions in this area.
Centrifugal fans are divided according to the direction of rotation:
- right (clockwise) rotation;
- left (counterclockwise).
Fans are also divided by the type of drive mechanisms:
- belt;
- straight;
- adjustable.
Fans are divided according to pressure level and distinguish the following types:
- high (3 kPa - 12 kPa);
- medium (1 kPa - 3 kPa);
- low (up to 1 kPa) pressure.
According to the direction of movement of air flows, fan installations are classified as follows:
- exhaust;
- and double-sided suction.
And there are also installations for use in aggressive environments, and most of these units highly specialized, and are intended only for operation in one, specific environment, for example, an environment chlorine. Installations for it are made of materials that are resistant to chlorine, and if you use such a unit for work in a different aggressive environment, it is far from the fact that it will maintain the tightness of the working chamber and will not come out of building.
Conventional fans are designed for operation at gas temperatures up to 80 degrees, and the content of solid impurities in it is not more than 100 mg per cubic meter. There are also installations for use in dusty environments, the so-called. dust fans, in which the content of solid impurities in the working medium is limited to one kilogram per m³. Also worthy of mention are explosion-proof rotary fans with pneumatic drive, used in mine ventilation, and in other explosive enterprises.
There are also significant differences in drives, the simplest and most reliable of them is direct. In it, the impeller is installed directly on the motor shaft, there is practically nothing to break. The disadvantage of this drive still exists - the need to have a speed controller for the motor if there is a need for power adjustment fan installation, since the design of the drive does not allow changing the speed of rotation of the impeller without changing the speed engine.
The next is the belt drive, its reliability is lower than that of the direct one (the belt can jump off the pulley or break), but it is already possible to change the rotor speed without changing that of engine. Consists of two pulleys (the first is on the motor shaft, the second on the same shaft with the impeller), which have several grooves with different diameters, by throwing the belt between which, you can change the gear ratio, thereby changing the fan speed without affecting engine.
The last type of drive, the most modern of all, is variable. In it, the transmission of rotational movement is carried out through a magnetic or hydraulic clutch located between the shafts of the motor and fan. Since such a drive is technically more complicated than all the previous ones, a microcontroller is used in it for ease of control, which makes it possible to use fans with such a drive in centralized systems where the function of remote management.
As for the difference between double-suction and exhaust fan units, it is obvious: at the exhaust gas intake occurs from one end, and at the first - from both.
Operating principle
It will be difficult to find a device that is simpler to operate than a centrifugal fan, the principle of which is as follows: gas is sucked in through an intake hole, then it hits the rotating rotor with blades located on it, passing through the channels between them, due to the centrifugal force, the gas gains acceleration, and leaves the rotor. Then it is collected by the casing and thrown out into the outlet.
