Fans are devices appointed to transport air, gas or other air mixtures through air conductors or without them, creating an overpressure of varying magnitude.
In industry, they are used, in particular, to ventilate rooms, purify air in rooms and in mines and stagnant areas of quarries, to create artificial draft in boiler furnaces, to create a flow of gas (air) in technological devices, pneumatic trauma units, etc.
The construction of fans must meet the requirements of standards, specifications, technical documentation, including working drawings.
Aerodynamic, acoustic, and vibration characteristics of the manufactured fans must meet the requirements of the applicable regulatory and technical documents for them.
Types and kinds
In ventilation systems, fans are appointed to transport air from the intake source to the room. These are devices for moving gases with a compression ratio of no more than 1.5 (i.e., the pressure difference at the inlet and outlet must be greater than 15 kPa). If the air is supplied by means of air conductors, they must be selected in such a way that the flow of supplied air can overcome the resistance of the ventilation network, which is created by bends and turns of air conductors, the presence of grilles, filters, etc. The resistance of the network causes a pressure drop, and the value of this drop is a determining factor in the choice of this device.
Axial fans
They are simple in construction, technologically advanced and cheap to manufacture, which largely determines their widespread use. The construction provides for the movement of the air inlet and outlet along the motor axis.
The world’s first axial fan was installed and successfully used in England in 1734. They are still used in various fields of activity. In addition to solving the issues of ventilation of premises, they are widely used in the ventilation of apartments, in the cooling of electronics, in air handling conductors, used in turbofan aircraft installations, mounted in wind tunnels, etc.
The most pronounced example of an axial fan is a propeller one. It has a low efficiency, which can be increased by embedding it in a cylindrical housing (in this case, the efficiency of the propeller type increases to 75%). If you attach blade guides directly behind the impeller, its efficiency will increase by another 10%.
Radial fans
It was first launched in 1835 and was used to ventilate an Altai mine. The construction and performance initially suggested its use for industrial purposes. This is primarily due to the fact that they are able to create a fairly high total pressure due to the shape of the impeller and blades.
The air sucked in through the intake port is also rotated by the specially shaped blades and ejected at right angles to the intake port by centrifugal force.
The blades can have different shapes and positions relative to the rotor axis. In the first case, the blades are bent backward. The performance depends heavily on the air pressure. They are not recommended for use with polluted air. While maintaining low noise characteristics, their efficiency reaches 80%.
Radial fans with backward curved blades are most efficient in a narrow spectrum located on the left side of the efficiency curve. And those with straight blades bent backward are very effective for handling polluted air. In this case, you can achieve an efficiency of up to 70%.
Straight radial blades prevent contaminants from sticking to the impeller. This type of blades can achieve an efficiency of up to 55%. When the blades are curved forward, pressure changes have a negligible effect on air volume. And with the impeller bent forward, they have smaller dimensions than the previous ones and have optimal performance on the right side of the efficiency graph, and is approximately 60%. Today, this type of equipment is widely used for production purposes.
Diagonal fans
It is a synthesis of radial and axial. The air passing through it moves in the axial direction and then is deflected by 45° in the impeller. The radial impeller increases the static pressure due to centrifugal force acting in the radial direction. The efficiency is up to 80%.
Diametric (tangential) fans
As a rule, they have an oblong cylinder shape and a “squirrel cage” rotor – hollow in the center and blades along the periphery. Instead of walls, they have blades bent forward. Air is drawn in from the front. The air is captured by the rotating blades and then accelerated in the desired direction by the diffuser.
They produce a uniform air flow along the entire length of the rotor and have the lowest noise characteristics. Despite the small diameter of the impeller, the diameter type is capable of delivering significant volumes of air. The pressure generated by them is relatively low, and tangential fans are mainly used in systems where air pressure is not important – air curtains, air conditioners, fan coil units, etc. Their efficiency level can reach 65%.
Other types of fans
Depending on the construction and purpose, the fans can be floor standing, wall-mounted, ceiling-mounted, ducted, or roof-mounted.
Thus, the simplest example of apartment ventilation is the use of a table or floor type. They usually do not have a guide housing and serve only to mix air masses in the room.
Ventilation of apartments is slightly more efficient when fans are installed in window openings, vents or special holes in the wall. In this case, they work to remove air from the room, and fresh air is supplied by natural infiltration – the inflow of air through leaks in the building elements.
If the air is only removed from the room and replaced with new air naturally, ventilation is called exhaust ventilation. Otherwise, when air is forced into the room by means of a ventilation system, ventilation is called supply ventilation.
As a rule, an air handling conductor uses a duct system to supply fresh air. The air handling conductor allows for the intake of fresh air, its preliminary processing (filtration, heating or cooling, humidification or dehumidification) and transportation to the premises. The simplest air handling conductor consists of a housing, a fan, a filter and a heater (electric heater). Apartment ventilation is most efficient and optimal when the volumes of exhaust and supply air are balanced. That is, both the air handling conductor and the exhaust ventilation work simultaneously with the same performance. Such systems are called supply and exhaust systems.
According to the construction, fans are divided into multi-zone, duct and rooftop fans.
A distinctive feature of multi-zone fans is the casing that allows you to connect several air conductors simultaneously. The multi-zone type is indispensable at facilities where air extraction (or vice versa) must be done from several rooms at once. Their use allows you to optimize air conductor networks and reduce the cost of operating the entire ventilation network as a whole.
Duct fans are the most common type of equipment for installation in round and rectangular ventilation ducts. They can be either axial or radial. Due to their small size, they can be mounted directly in the intersection of air ducts.
Rooftop fans, by definition, are designed to be installed on the roofs of buildings. Due to the more severe operating conditions (precipitation and constant wind loads), their casing is made of corrosion-resistant materials – galvanized or galvanized steel, protective epoxy coatings, etc. They can be used both for general ventilation and local ventilation, which include ventilation and exhaust of fireplaces, stoves, gas boilers and similar equipment.
Depending on the requirements and operating conditions, each type of fan may have additional construction features, such as fireproof construction, increased resistance to vibrations, reduced noise characteristics, smoke extraction, materials suitable for aggressive or dusty environments, etc.