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Fans are devices designed to transport air, gas, or other aerosomes through or without air ducts, thus creating excessive pressure of different magnitudes.
By way of creating excess pressure and air flow fans are divided into three main types. In non-channel ventilation systems, the most commonly used axial fans, in the channel - centrifugal fans (radial), and in the heat curtains, fan coils, indoor air conditioners are most often used diametrical fans (diagonal).

Diameter fans (diagonal fans)

Diametric fans, or, as they are called, diagonal fans, have a drum-type impeller and an asymmetrical knee-shaped body. Diagonal fans have a design with asymmetrical impeller location diametrical fans, they are diagonal fans, which provides air flow to the smaller section. Diameter fans with wide wheels can be connected directly to air ducts that have a cut in the form of an elongated rectangle and can create significant pressures even at low circumferential speeds of the working wheels but have a low efficiency.

Axial fans

Axial fans move the airflow along the axis of the impeller driven by the electric motor. By default axial, fans can be divided into home and axial fans industrial fans. Because of the low domestic axial fanspressure that creates axial fans (up to 50 Pa) they are used mainly in non-channel ventilation systems or in systems with a small length of air ducts (up to 5m), for example, bathrooms, bathrooms, showers, offices, sinks, warehouses, etc.

Centrifugal fans (radial fans)

Centrifugal fans (radial) have such a design in which the movement of air occurs due to centrifugal forces that arise when rotation of the impeller. The transformation of the kinetic energy of air into a potential, that is, increasing the air pressure with a decrease in speed is provided by the part of the expanding body - a diffuser.
The centrifugal impellers, as well as the axial and diagonal fans, are connected to the engine either directly (rigid couplings, elastic couplings) or through the transmission (belt, mechanically adjustable).
Radial fans consist of two main parts - a spiral body (the so-called "snail") and a worm wheel with vanes that can be bent forward or backward during wheel rotation.
By way of air sampling centrifugal fans radial fans (centrifugal) there are one-way and two-way suction, by the direction of rotation of the wheel - right and left rotation, created by the difference of total pressures: low pressure (up to 100 Pa); medium pressure (up to 300 Pa) and high pressure (up to 1500 Pa); by appointment - centrifugal fans of general purpose and special radial fans.
Centrifugal fans general purpose are used to transfer air or other non-aggressive gas mixtures containing dust or other solid particles not more than 100 mg/m3 and a temperature not more than 80oC. They are made of coal steel. By the size of the impeller, the number assigned to the fans is from 2.5 to 20.
Special radial fans are: dust fans - for moving dust and air mixtures; for roof centrifugal fans - smoke exhausters work in aggressive environments, - fans from corrosion-resistant steel; spark-and-explosion-proof fans - made of aluminum or heterogeneous metals; blower fans; shaft fans; Smoke exhausters operating up to two hours or more at ambient temperatures of 400oC.

The main characteristics of the fans are:
- volume flow of air;
- press;
- efficiency factor (efficiency) of the fan;
- frequency of rotation;
- speed sound pressure.

Centrifugal fans with curved forward blades have high flow rates and air pressure, with increased feed increases and pressure, but low efficiency, engine overheating and high noise levels are possible. Centrifugal fans with rearward-shovel blades have high efficiency, low noise, and with increasing supply the power does not change, but the pressure decreases. Centrifugal fans with radial endings also have high efficiency and low noise, with increasing supply pressure does not change, but increases power consumption and noise.

round channel centrifugal fans fansThe above characteristics of the fans are presented graphically, in the form of an individual characteristic of the fan, most often in the form of a dependence of its performance on the pressure output and rotational speed impeller.

It should be noted that now in most rectangular channel centrifugal fansmanufacturers of ventilation equipment in the range are fairly well-presented channel centrifugal fans for circular cross-section channels (diameter from 100 to 400mm) and air ducts of a rectangular cross section (from 300x150 to 1000x500mm). It expanded the scope of their application from domestic to larger industrial ventilation systems.

Fans of mixed type (centrifugal axial fans)

In recent years, fans of a mixed type, so-called centrifugal and axial fans have been widely used in channel household and semi-industrial vent systems with round air ducts. Thanks to their blended type fans a special air structure under the influence of centrifugal force is directed along the engine's axis. These fans are compact enough and create a decent pressure, which allows them to be used in systems with air ducts much longer than for axial fans.

At present there is a large number of both foreign and domestic manufacturers of ventilation equipment. Some manufacturers are known throughout the world for decades; others are only beginning to actively develop their production. Nevertheless, the market of ventilation equipment is actively developing, technologies and quality of products are being improved. Do not bypass this industry and trends in the introduction of new energy-saving technologies (recuperators, EC-fans etc.)

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