Fan is input dependentmechanical energyIt is a driven fluid machine, which increases the gas pressure and discharges gas.Exhaust pressureLess than 1.5 × 10 ^ 4 Pa.Modern ventilators are widely used for ventilation, dust discharge and cooling of factories, mines, tunnels, cooling towers, vehicles, ships and buildings, and for ventilation and induced draft of boilers and industrial furnaces,Air conditioning equipmentAnd cooling and ventilation in household electrical equipment, drying and delivery of grain, wind source of wind tunnel and inflation and propulsion of hovercraft.[1]
Fans are widely used in factories, mines, tunnelsCooling towerVentilation, dust discharge and cooling of vehicles, ships and buildings;Ventilation and induced draft of boiler and industrial furnace;Cooling and ventilation in air conditioning equipment and household appliances;Drying and selection of grain;Wind source of wind tunnel and inflation and propulsion of hovercraft.The following is the product parameters of the ventilator for a low-noise post.
Product name
Low noise post ventilator
Voltage
380V
power
3kw
speed
1420r/min
Total pressure
315pa
Air volume
24500 m3/h
noise
≤78dB（A）
weight
45kg
working principle
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Square duct ventilator
Working principle andTurbine compressorBasically the same, but because the gas flow rate is low and the pressure changes little, it is generally unnecessary to consider the change of gas specific volume, that is, the gas is regarded asIncompressible fluidhandle.
throughFanRelation with fanGas conveying machineryThe common abbreviation of "fan" includes fan,Blower, compressor andRoots blower, but excluding piston compressor, etcvolumeType blower and compressor.Fan is a product type of fan, but people usually call the fan barrel fan, which is another name of fan.
performance
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The performance parameters of ventilator mainly include flow, pressure, power, efficiency and speed.In addition, the noise and vibration are also the main technical indicators of the ventilator.Flow, also known as air volume, is expressed by the volume of gas flowing through the fan in unit time.Pressure, also known as wind pressure, refers to the pressure rise value of gas in the fan, including static pressure, dynamic pressure and total pressure.The total pressure is equal to the difference between the total pressure of the airflow on the outlet section and the inlet section of the fan;The static pressure is equal to the difference between the static pressure of the airflow on the outlet section and the inlet section of the fan;Dynamic pressure refers to the dynamic pressure of the average velocity of air flow on the outlet section of the fan.On the same section, the total pressure of air flow is equal to the sum of static pressure and dynamic pressure.
The flow, wind pressure, power, efficiency and other parameters have a certain functional relationship. When one of the parameters changes, other quantities also change.The relationship between them is drawn into a curve, which is called the performance curve.The shape of the performance curve is related to the type of fan.Changing the air volume and air pressure of the fan to meet the requirements of operating conditions is called performance regulation.There are five common adjustment methods. ①Place a throttle valve or damper in the intake pipe or exhaust pipe to control the flow.This method is the simplest, but the adjustment effect is poor. ②Place a deflector in front of the impeller inlet to change the airflow direction. ③Change the fan speed.This method has the best economic performance, but it is more complex.Consider changing the speedImpeller strengthAnd motor load conditions. ④Change the impeller width.When the working condition can be changed, the use efficiency of the fan changes little, but it is more complex. ⑤Change the installation angle of moving blade.This method has the highest equipment cost and the most complicated maintenance, but it has large flow variation range and good economy. It is generally used for largeAxial flow fan。
classification
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Air flow direction
Centrifugal fan
According to the different directions of gas flow, fans are mainly divided into centrifugal, axial, diagonal and cross flow types.
Centrifugal fan is a kind of modern society that uses a power machine (mainly a motor) to drive the impeller to rotate in the volute casing, and air is sucked in from the center of the impeller through the suction port.Due to the dynamic action of the blade on the gas, the gas pressure and speed can be increased, andcentrifugal forceUnder the action, it is thrown to the casing along the blade channel and discharged from the exhaust port.Because the flow of gas in the impeller is mainly in the radial plane, it is also called radial flow fan.
Centrifugal fan is mainly composed of impeller and casing. The impeller of small fan is directly installed on the motor. Medium and large fans pass throughcoupling Or the belt pulley is connected with the motor.Centrifugal fan generally adopts single-sided air intake and single-stage impeller;Double side air intake is available for large flow, and two back-to-back impellers are used, which is also called double suction centrifugal fan.
The impeller is the main component of the fan, and its geometric shape, size, number of blades and manufacturing accuracy have a great impact on the performance.The static balance and dynamic balance correction of the impeller can ensure the smooth rotation of the fan.According to the different outlet directions of blades, impellers are divided into three types: forward, radial and backward.The top of the blade of the forward impeller inclines to the rotation direction of the impeller;The top of the blade of the radial impeller is radial, which is divided into straight blade and curved blade;The top of the blade of the backward impeller inclines to the opposite direction of the impeller rotation.
Duct ventilator
The pressure generated by the forward impeller is the largest. When the flow and revolution are fixed, the required impeller diameter is the smallest, but the efficiency is generally low;Contrary to the backward impeller, the pressure generated is the smallest, the impeller diameter required is the largest, and the efficiency is generally higher;The radial impeller is between the two.The straight blade is the simplest and the wing blade is the most complex.
In order to have a proper velocity distribution on the blade surface, curved blades, such as equal thickness circular blades, are generally used.The impeller usually has a cover plate to increase the strength of the impeller and reduce the gas leakage between the blade and the casing.The connection between blade and cover plate shall be welded or riveted.The welded impeller has light weight and smooth flow channel.The impellers of low and medium pressure small centrifugal fans are also made of aluminum alloy.
(2) Axial flow fan
Axial flow fanWhen working, the power machine drives the impeller to rotate in the cylindrical casing, and the gas enters from the collector, gets energy through the impeller, increases the pressure and speed, and then discharges along the axial direction.There are three types of axial flow fans: vertical, horizontal and inclined. The diameter of small impeller is only about 100 mm, and that of large impeller is more than 20 m.
Axial flow fan
Small low-pressure axial fan is composed of impeller, casing, collector and other parts, and is usually installed on the wall or ceiling of buildings;Large high-pressure axial fan is composed of collector, impeller, streamline body, casing, diffuser and transmission parts.The blades are evenly arranged on the hub, and the number is generally 2~24.The more blades,wind pressureHigher;The blade installation angle is generally 10 °~45 °. The larger the installation angle,Air volumeAnd wind pressure.The main parts of axial flow fan are mostly welded or riveted with steel plates.[2]
(3) Diagonal fan
Diagonal fanAlso called mixed flow fan, in this type of fan, the gas enters the impeller at an angle to the axis, gets energy in the blade passage, and flows out along the inclined direction.The shape of the impeller and casing of the fan is conical.This fan has the characteristics of both centrifugal and axial flow, and its flow range and efficiency are between the two.
(4) Cross flow fan
Pneumatic fan
Cross flow fan is a small high-pressure centrifugal fan with forward multi blade impeller.Gas fromrotorOne side of the outer edge enters the impeller, and then passes through the inner part of the impeller and is discharged from the other side. The gas in the impeller is subjected to the force of the blade twice.Under the same performance conditions, it has small size and low speed.
Compared with other types of low-speed fans, cross flow fans have higher efficiency.Its axial width can be arbitrarily selected without affecting the flow state of the gas, and the gas still flows evenly across the entire rotor width.Its exit section is narrow and long, suitable for installation in various flat equipment for cooling or ventilation.
The performance parameters of the fan mainly include flow, pressure, power, efficiency and speed.In addition,NoiseAnd the vibration is also the main technical index of the fan.Flow, also known as air volume, is expressed by the volume of gas flowing through the fan in unit time;Pressure, also known as wind pressure, refers to the pressure rise value of gas in the fan, including static pressure, dynamic pressure and total pressure;Power refers to the input power of the fan, namelyShaft power。ventilatorEffective powerThe ratio to shaft power is called efficiency.Total pressure efficiency of fanUp to 90%.
The future development of fans will further improve the aerodynamic efficiency, device efficiency and use efficiency of fans to reduce power consumption;The large centrifugal fan is replaced by an axial fan with adjustable moving blades;Reduce fan noise;Improve the wear resistance of the impeller and casing of the smoke and dust exhaust fan;Realize variable speed regulation and automatic regulation.
2. Medium pressure centrifugal fan: the fan inlet is a centrifugal fan with standard atmospheric conditions and the total pressure of the fan is 1kPa<PtF<3kPa.
3. High pressure centrifugal fan: the fan inlet is a centrifugal fan with standard atmospheric conditions and the total pressure of the fan is 3kPa<PtF<15kPa.
4. Low pressure axial fan: the fan inlet is under standard atmospheric conditions, and the total pressure of the fan is PtF ≤ 0.5kPa.
5. High pressure axial fan: the fan inlet is under standard atmospheric conditions, and the total pressure of the fan is 0.5kPa<PtF<15kPa.
Scale size
Specific speed refers to the speed required to reach unit flow and pressurespeed。
Low specific speed fan (ns=11~30) 2. Medium specific speed fan (ns=30~60) 3. High specific speed fan (ns=60~81)
Use classification
According to the purpose of the ventilator, it can be divided into induced draft fan (Y), textile fan (FZ) and fire protection fanSmoke exhaust fanEtc.The use of ventilator is generally represented by the prefix of Chinese Pinyin.
Development trend
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① Further improve the aerodynamic efficiency, device efficiency and use efficiency of the ventilator to reduce power consumption;
② The large centrifugal fan is replaced by an axial fan with adjustable moving blades;
③ Reduce fan noise;
④ Improve the wear resistance of the impeller and casing of the smoke and dust exhaust fan;
⑤ Realize variable speed regulation and automatic regulation.[3]
Development history
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Fans have a long history.More than 2000 years ago,Babylon, Cuba, China, Persia and other countries have used the ancient windmill to carry water for irrigation and grind grains.
In 1862, British Guibel invented the centrifugal fan. Its impeller and casing are concentric circles. The casing is made of bricks. The wooden impeller uses straight backward blades. Its efficiency is only about 40%. It is mainly used for mine ventilation.
In 1880, people designed a volute casing for mine ventilation and a centrifugal fan with backward curved blades. The structure has been relatively perfect.
In 1898, the Irish designed the forward blade Sirocco centrifugal fan, which was widely used in various countries;In the 19th century, the axial flow fan has been applied to mine ventilation and blast in metallurgical industry, but its pressure is only 100~300 Pa, and its efficiency is only 15~25%. It did not develop rapidly until the 1940s.
In 1935, Germany first adopted axial flow equal pressure fan for boiler ventilation and induced draft;In 1948, Denmark made the axial-flow fan with adjustable blades in operation;Rotary axial flow fans, meridian accelerated axial flow fans, diagonal flow fans and cross flow fans have also been developed.[4]
application
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Explosion proof roof ventilator
Fans are widely used in various industrial sectors. Generally speaking, centrifugal fans are suitable for places with small flow and high pressure, while axial fans are commonly used for situations with large flow and low pressure.
1、 Boiler fan
The boiler fan can be centrifugal or axial flow type according to the boiler specification.According to its function, it can be divided into boiler ventilator - conveying air to the boiler;Boiler induced draft fan- Remove the smoke in the boiler.
2、 Ventilators for ventilation
This type of fan is generally used for ventilation, heating and ventilation of factories and various buildings. The pressure is not high, but the noise is low. Centrifugal or axial flow fans can be used.
This kind of fan requires high pressure, which is generally 2940~14700N/m2, that is, the range of high-pressure centrifugal fan.Due to the high pressure and large peripheral speed of the impeller, the impeller shall have sufficient strength during design.
It has two types: one is the main fan (also called the main fan), which is used for conveyingfresh air, its flow is large, and the axial flow type is more suitable, and the centrifugal type is also useful;The other is local fan (also known as local fan), which is used for ventilation of mine working face. Its flow and pressure are small, and explosion-proof axial fan is mostly used.
5、 Pulverized coal fan
Transmission thermal power station boilercombustion system Of pulverized coal, mostlyCentrifugal fan。The pulverized coal fan can be divided into two types according to different purposes: one is the storage type pulverized coal fan, which is used to blow the pulverized coal in the storage bin from its side to the furnace. The pulverized coal does not directly pass through the fan, so the fan is requiredExhaust pressureHigh;The other is a direct fired pulverized coal fan, which directly sends pulverized coal to the furnace.Due to serious wear of pulverized coal on impeller and shellWear-resistant material。
Faults and maintenance
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common problem
Wear resistance and wear resistance treatment of fans: Since a large number of fans are used for ventilation and dust removal in factories, mines, tunnels, etc., the impeller and casing of fans are worn to varying degrees, which directly affects the smooth progress of production in some places. Therefore, there are high requirements for wear resistance of fans.
Commonly used wear-resistant treatment includes surfacing, spraying, spray welding, coating polymer wear-resistant materials, etc., which can relatively extend the service life of the ventilator.In recent years, China has introduced an effective wear-resistant treatment method from abroad, that is, pasting or inlaying on the impeller or volute surfaceWear-resistant ceramicsBecause wear-resistant ceramics have good wear-resistant properties, the wear-resistant properties of the unit can be greatly improved.And pastedWear resistant ceramic sheetBecause of its convenient maintenance, its fan has been widely promoted and applied in relevant industries in China.
Solution
High polymer wear-resistant materials are often used for fan wear failures, which mostly refer toPolymer compositesFor example, it is mainly used to repair the abrasion of the fan drive part. Because the material has stronger adhesive force and compressive strength, it can be repaired without disassembly and machining. Compared with traditional methods, it has more advantages and avoids the impact of thermal stress of surfacing and the disadvantages of high requirements for spraying technology.At the same time, the polymer composite material has the concession of metal deficiency, which can well absorb the impact and vibration of the fan and avoid the secondary wear. It is increasingly mature in the application of solving the wear failure of the fan transmission part.
