Centrifugal fan: specifics of the device and principle of operation of the device

With the development of the industrial sector, a large number of technological processes required forced air supply.The household sector has not been left out either. Some types of communications require a regular supply of fresh air.

An elegant solution to this problem was a centrifugal fan, which is capable of autonomously pumping the required amount of air mass. But how is it designed and how does it work? It is these questions that we will examine in detail in our article.

Let's consider the design features of the device, its capabilities, scope of application, and the best manufacturers whose products are presented on the market. We will also give recommendations on choosing the appropriate fan model.

The essence of pumping and rarefying air with a fan

A fan is a mechanical structure that is capable of processing the flow of a gas-air mixture by increasing its specific energy for subsequent movement.

This architecture of the unit makes it possible to create the effect of injection or rarefaction of the working gas in space through an increase or decrease in pressure, respectively (energy conversion mechanism).

Gas pressure is understood as an endless process of chaotic movement of gas molecules, which, hitting the walls of a closed space, create pressure on them.

Therefore, the higher the speed of these molecules, the more impacts and the higher the pressure. Gas pressure is one of the main characteristics of gas.

On the other hand, any gas has two more parameters: volume and temperature. Volume is the amount of space filled by a gas. Gas temperature is a thermodynamic characteristic that relates the speed of molecules and the pressure they generate.

These “three pillars” are based on the molecular kinetic theory, which is the basis for describing all processes associated with the processing of gases and gas mixtures.

The injection process is a forced concentration of molecules in a confined space beyond a certain norm. For example, the generally accepted air pressure at the earth's surface is approximately 100 kPa (10⁵ kilo Pascals) or 760 mm Hg. Art. (millimeters of mercury).

As the altitude above the Earth's surface increases, the pressure decreases and the air becomes rarefied.

Atmospheric pressure is the weight of a column of air relative to the surface area over which it is located. Not mass, but weight P=mg. Measured by a barometer, other types of pressure are determined by a manometer

Rarefaction is the reverse process of pumping, during which molecules leave a closed system. The volume remains the same, but the number of molecules decreases significantly, therefore, the pressure decreases.

The pumping effect is necessary to force the movement of air. It is possible to move air through the rarefaction effect: to restore the pressure balance in the entire system, molecules move from a more concentrated area of ​​molecules to a less concentrated one.

This is how gas molecules move.

To determine the speed of air flow outside or inside a building, a special tool is often used - an anemometer. An indispensable device for designing ventilation systems

There are a variety of ventilation system layouts, but they can be divided into several classes according to certain parameters:

1. By appointment. There are general and special purpose fans. Fans are used for normal gas movement. Special fans are used for pneumatic transport, transportation of aggressive and explosive gas mixtures.
2. By speed. There are wheels with blades with low, medium and high specific rotation speeds.
3. By pressure range. There are known systems for generating low (up to 1 kPa), medium (1–3 kPa), high (more than 3 kPa) pressure.

Some industrial and domestic processes using blowers occur in extreme environmental conditions, so the corresponding requirements are put forward for the equipment.

Thus, we can talk about dust-proof, moisture-proof, heat-resistant, corrosion-resistant, spark-proof units and smoke removal devices and conventional fans.

Information about the types of fans is discussed in detail in another our article.

Centrifugal fan design

The centrifugal design system is a pumping mechanism with a radial architecture that is capable of generating pressure of any range.

Designed for transportation of mono- and polyatomic gases, including chemically “aggressive” compounds.

The design is “clad” with a metal/plastic casing, which is called a protective casing. The shell protects the inner chamber from dust, moisture and other substances that can negatively affect the operation of the unit.

A high-quality ventilation product always has a certain protection class. The degree of protection of the shell (Ingress Protection) is a unified international product quality standard that determines the level of protection of equipment from environmental influences.

The radial type fan develops significantly higher pressure than the axial version. This is due to the communication of a portion of the air entering the drum with energy generated during the transition from the input to the output of the system

The mechanism is driven by an electric motor or an internal combustion engine (typical of industrial fans). The most common method is an electric motor that rotates a shaft with an impeller.

There are several known options for transmitting rotational motion from the motor to the impeller:

• elastic coupling;
• V-belt transmission;
• continuously variable transmission (hydraulic or inductive slip clutch).

Considering the existence of a huge number of manufacturing companies that create unique systems with a wide variety of dynamic parameters, consumers have a fairly extensive range of fans at their disposal.

The housing has two main channels: input and output. The gas mixture enters the first channel, moves into the chamber, is processed there, and then exits into the other

As a result of the intensive work of the developers, we have a wide range of applications for such machines, including:

• ventilation and heating systems in private and multi-storey buildings;
• air supply and purification for non-residential buildings;
• filtration systems in agriculture;
• implementation of technological processes in light and heavy industry of various directions.

There are also options for using blowers in fire suppression systems and ultra-fast air replacement in confined spaces.

Such fans operate with high-temperature gas mixtures, which obliges manufacturers to include in the technical documentation information about the compliance of their equipment with international standards.

The proven and simple design of the centrifugal mechanism has a number of clear advantages:

• high reliability and unsurpassed performance;
• ease and accessibility of equipment maintenance;
• safety of integration and operation of units;
• minimal costs for energy resources and repairs in case of failure.

In addition, blowers have a fairly low noise threshold, which allows them to be used in domestic conditions.Centrifugal fans also have an exceptionally long service life due to the absence of direct contact of the working parts of the mechanism in the working chamber.

Features of the device operating cycle

Let's look at the general operating principle of a centrifugal blower with a radial design. Note that experts distinguish between two main fan designs: with an axial and radial placement of the inlet into which the air flow is sucked.

This primarily affects the option of installing the fan in the system and has virtually no effect on the overall performance.

A radial fan can work both with ordinary air, which it takes from the space, and with flow air that goes through the air duct (the effect of balancing areas with different pressures)

The axial inlet is typical for general purpose positive displacement blowers. Radial placement of the flow inlet is typical for mainline blowers.

During the first stage of the fan operating cycle, air flow moves onto the surface of a rapidly rotating impeller. The impeller blades divide the air into small volumes that move inside the working chamber.

Here the air mass accumulates, that is, the air mass is directly compressed into a small volume.

The design of the unit body itself has its own characteristics.

The two most common hull shapes are known:

• rounded;
• spiral.

The rounded shape of the housing is typical for fans that move a huge amount of air in a short process time. And the spiral shape is inherent in fans, which additionally compress the air volume and generate medium and high pressure.

At the second stage, air is pumped into the working chamber. As is known, at a constant volume, with an increase in the total mass of gas molecules, the number of collisions of molecules increases, and therefore their speed increases. Consequently, the gas pressure also increases.

The shape and number of blades are of great importance. Without exception, all impeller options are tested in wind tunnels to determine optimal operating conditions

At the final stage, the compressed gas is removed from the working chamber to the outlet. Then the air passes into the central air duct and moves in the indicated direction.

The rarefaction process occurs exactly the opposite. Air is taken from an air duct or confined space where a rarefied area needs to be created and discharged into the environment or other confined space.

Centrifugal Fan Specification

Compressor systems are characterized by a number of structural and dynamic differences that must be taken into account when selecting and implementing them into the ventilation system.

The specifications include:

• the design of the blower itself;
• engine's type;
• Control block;
• placement of the impeller and transmission of rotational motion from the motor;
• angle of location of the inlet and outlet pipes;
• the material from which the product parts are made, its dimensions and weight.

Experts also pay attention to the compliance of products with international standards: ISO/IEC and GOST standards, IP markings, ATEX directives, etc.

Dynamic features include technical parameters of the blower performance: generated pressure and pressure drop coefficient, speed and maximum flow temperature, shaft speed and sound pressure level, efficiency and engine power

Discharge pressure is the maximum value that the fan is capable of creating during operation in nominal mode.

P_v = P_sv +P_dv,

Where: P_v - total pressure, P_sv - static pressure, P_dv — dynamic pressure.

Differential coefficient - the difference between the input and generated pressure (bar).

Volumetric air flow is the amount of gas mixture that moves per unit of time (productivity). Usually calculated in m³/h for domestic producers, liter/min for foreign ones.

Rotation frequency is the number of full revolutions of the impeller per unit time. Calculated in pcs/s or Hz. It must be remembered that the load level of the air fan should not exceed 75% of the maximum.

Working for a long time in overload mode with a high rotation speed, the fan overheats and can quickly fail. But this process can be controlled by managing it at your own discretion. What is it used for? speed controller fan

Sound pressure is the noise level from rotating parts and air friction between metal. Measured at a distance of 3 meters from the source when it is operating at maximum load. Noise must be taken into account when choosing a constantly running fan.

Most equipment is equipped with noise and background sound absorbers. Noise standards: no more than 50 dBa for domestic premises and no more than 75 dBa for industrial premises

One of the devices with a miniscule noise level is bladeless fan.

The fan efficiency is the product of the following three coefficients:

• losses in air flow;
• leaks through gaps in the structure;
• mechanical efficiency of the product.

For centrifugal fans, the overall efficiency is in the range from 0.7 to 0.85, for axial (channel) fans - no more than 0.95. When choosing a radial fan, it is necessary to take into account the safety factor of the electric motor of 1.2. That is, select the electric motor power 20% more than required.

The power of the fan motor is determined by the formula:

N = (Q*P)/(102*3600*efficiency),

Where: Q — productivity (volume air flow), P — generated pressure.

Selection of fan according to requirements

The process of selecting ventilation equipment for an industrial facility (workshop, hangar) is a rather interesting and intricate process that must be done by a specialist. Features of ventilation of industrial premises in detail reviewed here.

There are already ready-made solutions for ordinary apartments and private houses. In the general case (for a 2-3 room apartment) we have the following architecture of the ventilation system:

• ventilators are installed in living rooms, the number of which depends on the size of the premises and the number of residents;
• exhaust diffusers are integrated in the kitchen and bathroom plus they are laid air ducts to the air handling unit.

A centrifugal fan includes a control unit, a filter system for air purification, an electric motor and the radial fan itself.

For the above ventilation system, wall-mounted fans of the CF series produced by Vents with a capacity of up to 120 m3 are suitable.³/hour

The current market for ventilation equipment is represented by a wide range of foreign-made companies: Systemair, Soler&Palau, OSTBERG, Rosenberg, HELIOS, Maico, Ruck Ventilatoren GmbH, AeroStar, Blauberg, Elicent, Rhoss, Frapol, CMT CLIMA, HygroMatik GmbH, Winterwarm, Tecnair LV, AERIAL GmbH , MITA.

Products from these companies will be an excellent solution for ventilation problems of any scale.

Domestic brands Vents, Elkom, Domovent and Veza are not inferior to them in the quality of production and reliability of equipment. If you have any doubts about the accuracy of the calculations made or the choice of a specific model, we recommend contacting the support service of any of the companies.

If you are the owner of a private 1-2 storey building, industrial or commercial building of a similar area (restaurant, warehouse, canteen, cafe, office), when choosing equipment, you must take into account the volume of the premises, the air exchange rate, the length and cross-section of the main pipelines.

The tasks of ventilation and smoke removal can be easily handled by multi-zone blowers or roof fans of the KROM series from the Veza company, fans of the VN series from the Vents company and others

Be sure to pay attention to the additional functionality of centrifugal fans and the possibility of integration into a variety of air conditioning systems.

Thus, radial blowers can be equipped with auxiliary components:

• adjustable timers and interval switches, photo sensors and humidity detectors;
• speed controllers and status indicators;
• sensors for electric motor overload and lack of electrical power supply;
• spring vibration absorbers or rubber vibration isolators.

If the fan is placed inside an apartment or house, it can be covered with a removable front decorative panel made of aluminum or plastic, taking into account the interior of the room.

For many users, an important criterion when choosing a fan is the noise level. Are you looking for a quiet fan for your bathroom? We recommend that you familiarize yourself with the rating silent fans.

Conclusions and useful video on the topic

In the following video, Elcom specialists clearly talk about centrifugal fans:

Below is an excellent example of installing a household fan in a bathroom:

Another option for installing a low-power household fan in an apartment:

The classic centrifugal fan is the result of many years of experience in the design and production of ventilation equipment. This is not only an excellent solution for industry, but also an optimal air transport tool for residential and office premises.

Are you thinking about purchasing a centrifugal fan? Or did you notice a discrepancy in the disassembled material? Ask your questions and clarify technological aspects in the comments section.

Or maybe you have already installed such a fan in the bathroom? Are you satisfied with his work? Have you chosen the correct power of the device for your room? Send a photo of your fan and leave your comments.