With the development of the industrial sector, a large number of technological processes have demanded a forced supply of air. The household sphere did not stand aside either. Some types of communications require a regular supply of fresh air.
An elegant solution to this problem has become a centrifugal fan, which is capable of autonomously injecting the necessary amount of air mass. But how does it work and how does it work? These are the questions we will discuss in detail in our article.
Consider the design features of the device, its capabilities, the scope of application, the best manufacturers whose products are on the market. And also give recommendations on the choice of a suitable fan model.
The content of the article:
- The essence of the discharge and air dilution fan
- Centrifugal fan design
- Features of the operating cycle of the device
- Centrifugal Fan Specification
- Fan selection according to requirements
- Conclusions and useful video on the topic
The essence of the discharge and air dilution fan
The fan is a mechanical structure that is capable of processing the flow of gas-air mixture by increasing its specific energy for subsequent movement.
This architecture of the unit provides the ability to create the effect of pumping or diluting the working gas in space through an increase or decrease in pressure, respectively (the conversion mechanism energy).
By gas pressure, we understand the endless process of the chaotic movement of gas molecules, which, hitting the walls of a closed space, creates pressure on them.
Consequently, the higher the speed of these molecules, the more shocks and the higher the pressure. Gas pressure is one of the main characteristics of gas.
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Centrifugal fans - the simplest version of the mechanical devices used in the arrangement and organization of ventilation systems, differing in purpose, volume and type of air movement
Radial, they are centrifugal, fans allow you to implement a variety of projects of supply and exhaust ventilation. Mainly used without air ducts.
The centrifugal fan operation is controlled by an engine whose power is selected depending on the volume of the air mass being moved.
Centrifugal fans are manufactured for operation both in clean air without impurities and in explosive complex environments.
The simplest type of fan
Fan installation at a manufacturing plant
Centrifugal fan motor
Varieties of radial fan units
On the other hand, any gas has two more parameters: volume and temperature. Volume - the amount of space that is filled with gas. Gas temperature is a thermodynamic characteristic that relates the velocity of molecules and the pressure generated by them.
On these “three whales” there is a molecular – kinetic theory, which is the basis for describing all the processes associated with the processing of gases and gas mixtures.
The process of injection is a forced concentration of molecules in a closed space above a certain norm. For example, the generally accepted air pressure at the surface of the earth is approximately 100 kPa (105 kilo Pascal) or 760 mm Hg. Art. (millimeters of mercury).
With an increase in height above the surface of the Earth, the pressure becomes less, the air becomes rarefied.
Atmospheric pressure is the weight of the air column relative to the surface area above which it is located. Not mass, namely weight P = mg. Measured by a barometer, other types of pressure are determined by a manometer.
Vacuum is the reverse process of injection, during which molecules leave a closed system. The volume remains the same, but the number of molecules decreases several times, therefore, the pressure decreases.
The effect of pressure is necessary for the forced movement of air. It is possible to move the air through the vacuum effect: to restore the pressure balance during the entire system, molecules move from a more concentrated region of molecules to less concentrated.
In this way, the movement of gas molecules.
To determine the flow rate of air outside or inside the building, they often use a special tool - an anemometer. An indispensable device for the design of ventilation systems
There are a variety of different arrangements of ventilation systems, but they can be divided into several classes according to certain parameters:
- To destination. There are general and special fans. Fans are used for the usual movement of gas. Special fans are used for pneumatic conveying, transportation of aggressive and explosive gas mixtures.
- By speed. There are with small, medium and high specific frequency of rotation of the wheel with blades.
- By pressure range. The systems of generation of low (up to 1 kPa), medium (1–3 kPa), high (more than 3 kPa) pressure are known.
Some industrial and domestic processes with the use of blowers occur in extreme environmental conditions, so the equipment requirements are put forward.
Thus, it is possible to speak about dust, water-proof, heat-resistant, corrosion-resistant, spark-proof units and smoke removal devices and conventional fans.
Information about the types of fans discussed in detail in another our article.
Centrifugal fan design
The centrifugal design system is an injection mechanism with a radial architecture that can generate pressure of any range.
Designed to transport mono-and polyatomic gases, including chemically “aggressive” compounds.
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Centrifugal fans are used in the ventilation systems of buildings of the municipal, industrial, and commercial categories. Serve for the supply of fresh air and the extraction of harmful volatile substances.
The motor and the fan housing are located on the welded and cast frame of the ventilation unit. There are bearings between them.
The impeller of the ventilation unit is essentially a hub that is rigidly connected to the main drive.
The impeller of the radial fan is mounted on the carrier shaft, on which the bearings are located
The blades of the centrifugal fan are fixed on the front and main rotating disk. They can be curved forward, backward or radial.
Centrifugal fans are divided in the direction of rotation of the impeller on models with right and left rotation. In most fans, the direction can be changed
Fans with one-sided suction type are different cantilever impeller installation option. Most of them are small and relatively small constructions.
Ventilation systems with double-sided suction type are characterized by a central location of the rotating wheel relative to the bearings. Usually this is a large design.
Typical centrifugal fan
The location of the engine and the body on the frame
Top view of centrifugal fan
Impeller centrifugal fan
Blades of the impeller fan
Left execution of the centrifugal fan
Single suction fan
Double suction radial fan
The design is “dressed” with a metal / plastic casing, which is called a protective casing. The shell protects the inner chamber from dust, moisture and other substances that may adversely affect the operation of the unit.
High-quality ventilation product always has a certain class of protection. The degree of protection of the shell (Ingress Protection) - a single international standard for product quality, which determines the level of protection of equipment from environmental influences.
The radial-type fan develops significantly greater pressure than the axial variant. This is due to the message of the portion of the energy trapped in the air of the air generated during the transition from the inlet to the outlet of the system
The mechanism is driven by an electric motor or an internal combustion engine (typical for industrial fans). The most common method is the electric motor, which rotates the shaft with the impeller.
There are several variants of the transmission of rotational motion from the motor to the impeller:
- elastic coupling;
- V-belt transfer;
- continuously variable transmission (hydraulic or inductive slip clutch).
Given the existence of a huge number of manufacturing companies that create unique systems with a variety of dynamic parameters, at the disposal of consumers a fairly extensive range fans.
In the case there are two main channels: input and output. The gas mixture enters the first channel moves into the chamber, is processed there, and then goes into another
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;
- supply and purification of air for non-residential buildings;
- filtration systems in agriculture;
- performance of technological processes in light and heavy industry of various directions.
There are also options for the use of blowers in fire extinguishing systems and ultrafast air replacement in a confined space.
Such fans work with high-temperature gas mixtures, which obliges manufacturers include in the technical documentation information on the compliance of their equipment with international standards.
The proven and simple design of the centrifugal mechanism has several clear advantages:
- high reliability and unsurpassed performance;
- ease and availability of equipment maintenance;
- safety of integration and operation of units;
- minimum energy costs and repairs in case of failure.
In addition, the blowers have a rather low noise threshold, which allows them to be used in domestic conditions. Centrifugal fans also have an extremely long service life due to the lack of direct contact between the working parts of the mechanism in the working chamber.
Features of the operating cycle of the device
Consider the general principle of operation of a centrifugal blower of radial design. It should be noted that specialists distinguish two main fan designs: with axial and radial placement of the inlet, where the air flow is sucked.
This primarily affects the option of mounting the fan in the system and practically does not affect the overall performance.
The radial type fan can work as with ordinary air, which it takes from space, and with the flow of air that goes through the air duct (the effect of balancing areas with different pressure)
An axial inlet is typical for injection blowers for general use. The radial placement of the flow inlet is typical for mainline blowers.
At the first stage of the fan cycle, the air flow moves to the surface of the rapidly rotating impeller. The impeller blades divide the air into small volumes that move inside the working chamber.
Here there is an accumulation of air mass, that is, there is a direct compression of the air mass into a small volume.
The design of the housing unit itself has its own characteristics.
There are two common forms of housing:
- rounded;
- spiral.
The rounded shape of the case is typical for fans that move a huge amount of air in a short time during the process. And the spiral shape is inherent to the fans, which additionally produce air volume compression and the generation of medium and high pressure.
At the second stage, air is forced in the working chamber. As is known, with a constant volume, with an increase in the total mass of gas molecules, the number of collisions of molecules increases, and hence their speed increases. Consequently, the gas pressure also increases.
Of great importance is the shape and number of blades. One and all variants of impellers are tested in wind tunnels to determine the optimal operating conditions.
At the final stage, the compressed gas is withdrawn from the working chamber to the outlet. Then the air goes into the central duct and moves in the specified direction.
The process of dilution occurs exactly the opposite. Air is drawn from an air duct or enclosed space where it is necessary to create a rarefied area and is discharged into the environment or another confined space.
Centrifugal Fan Specification
Compressor systems are characterized by a number of structural and dynamic differences that must be considered when selecting and introducing them into the ventilation system.
Specifications include:
- directly the design of the blower;
- engine's type;
- Control block;
- placement of the impeller and the transmission of rotational motion from the motor;
- angle location of the inlet and outlet;
- the material from which the product details are made, its dimensions and weight.
Specialists also pay attention to the compliance of products with international standards: ISO / IEC and GOST standards, IP marking, ATEX directives, etc.
The dynamic characteristics include the technical parameters of the blower performance: the generated pressure and the coefficient differential pressure, speed and maximum flow temperature, shaft speed and sound pressure level, efficiency and power engine
The injected pressure is the maximum value that a fan is able to create during operation in nominal mode.
Pv = Psv + Pdv,
Where: Pv - total pressure Psv - static pressure Pdv - dynamic pressure.
Differential factor - the difference between inlet and generated pressure (bar).
Volume air flow is the amount of gas mixture that moves per unit of time (capacity). Usually calculated in m3/ h for domestic producers, liter / min - for foreign.
Rotation frequency - the number of complete rotations of the impeller per unit of time. Calculated in pieces / 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 the overload mode with a large rotational speed, the fan overheats and can quickly fail. But this process can be controlled by controlling it on your own. For what use speed controller fan.
Sound pressure - the level of noise from rotating parts and air friction metal. It is measured at a distance of 3 meters from the source when it is operating at maximum load. Noise must be considered when choosing a constantly running fan.
Most equipment is equipped with noise absorbers and background sounds. Norms for noise: no more than 50 dBA for domestic premises and no more than 75 dBA for industrial
One of the devices with meager noise level is bladeless fan.
The efficiency of the fan is the product of the three following factors:
- air flow loss;
- leakage 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, in axial (channel) fans - no more than 0.95. Choosing a radial fan, it is necessary to consider the safety factor of the motor 1.2. I mean pick up the power of the electric motor is 20% more than necessary.
The power of the fan motor is determined by the formula:
N = (Q * P) / (102 * 3600 * Efficiency),
Where: Q - performance (air volume flow), P - generated pressure.
Fan selection according to requirements
The process of selecting ventilation equipment for an industrial facility (work shop, hangar) is a rather interesting and intricate process that a specialist should do. Features of ventilation of industrial premises in detail reviewed here.
For ordinary apartments and private houses, ready-made solutions already exist. In the general case (for 2–3 room apartments) we have the following architecture of the ventilation system:
- in the living rooms ventilators are installed, the number of which depends on the size of the premises and the number of tenants;
- exhaust diffusers plus lining are integrated in the kitchen and bathroom air ducts to the air handling unit.
The 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 fans of the VF series manufactured by Vents with a capacity of up to 120 m are suitable.3/hour
The current market for ventilation equipment is represented by a wide range of foreign 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, Elcom, Domovent and Veza are not inferior to them in the quality of production and reliability of equipment. If there are doubts about the accuracy of the calculations made or with the choice of a particular model, we recommend contacting the support service of any of the companies.
If you are the owner of a private 1–2 storey building, an industrial or commercial building of a similar area (restaurant, warehouse, dining room, cafe, office), when choosing equipment it is necessary to take into account the volume of rooms, the frequency of air exchange, the length and cross-section of main pipelines.
Ventilation and smoke removal tasks are easily handled by multi-zone blowers or roof fans of the CROM series from the company Wesa, fans of the HV series by the company Vents 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.
So, 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 motor overload and mains power failure;
- spring vibration absorbers or rubber vibration isolators.
If the fan is placed inside the apartment or house, it can be closed with a removable decorative aluminum or plastic front panel, taking into account the interior of the room.
For many users, the noise level is an important criterion when choosing a fan. Are you picking up a quiet fan in the bathroom? We recommend to familiarize with a rating. silent fans.
Conclusions and useful video on the topic
In the following video, Elcom specialists are available to talk about centrifugal fans:
The following is a great example of installing a household fan in a bathroom:
Another option for installing a low-power domestic fan in an apartment:
The classic centrifugal fan is the result of many years of experience in the design and manufacture of ventilation equipment. This is not only a great solution for the industry, but also an optimal air transport tool for residential and office space.
Are you thinking about purchasing a centrifugal fan? Or noticed a discrepancy in the material disassembled? Ask your questions, clarify the technological aspects in the comments block.
Or have you already installed such a fan in the bathroom? Are you satisfied with his work? Did you choose the right power of the device for your room? Send a photo of your fan and leave your comments.
