Classified by gas flow direction
According to the different flow directions of the gas, the fan is mainly divided into centrifugal type, axial flow type, diagonal flow type and cross flow type.
Centrifugal fan
When the centrifugal fan is working, the power machine (mainly the motor) drives the impeller to rotate in the volute casing, and the air is sucked from the center of the impeller through the suction port. Due to the kinetic action of the blades on the gas, the gas pressure and velocity are increased, and under the action of centrifugal force, the blade is raked toward the casing and discharged from the exhaust port. Since the flow of gas in the impeller is mainly in the radial plane, it is also called a radial flow fan.
The centrifugal fan is mainly composed of an impeller and a casing. The impeller of the small fan is directly mounted on the motor, and the large fan is coupled to the motor through a coupling or a pulley. Centrifugal fans are generally single-sided air intake, with a single-stage impeller; large flow can be double-sided intake, with two back-to-back impellers, also known as double-suction centrifugal fans.
The impeller is the main component of the ventilator, and its geometry, size, number of blades and manufacturing accuracy have a large impact on performance. The impeller is statically balanced or dynamically balanced to ensure that the fan rotates smoothly. According to the direction of the blade outlet, the impeller is divided into three types: forward, radial and backward. The top of the blade of the forward impeller is inclined toward the direction of rotation of the impeller; the top of the blade of the radial impeller is radial, and is divided into straight vane and curved vane; the top of the vane of the backward impeller is inclined to the opposite direction of rotation of the impeller.
The forward impeller generates the most pressure. When the flow rate and the number of revolutions are constant, the required impeller diameter is the smallest, but the efficiency is generally low. The reverse impeller is opposite, the generated pressure is the smallest, the required impeller diameter is the largest, and the efficiency is generally high. The radial impeller is somewhere in between. The profile of the blade is the simplest with straight blades, and the airfoil blades are the most complex.
In order to have a suitable velocity distribution on the surface of the blade, curved blades, such as arcs of equal thickness, are generally used. The impeller usually has a cover disk to increase the strength of the impeller and reduce gas leakage between the blade and the casing. The connection of the blade to the cover plate is welded or riveted. The welding impeller has a light weight and a smooth flow path. The impellers of low and medium pressure small centrifugal fans are also cast in aluminum alloy.
Axial fan
When the axial flow fan is working, the power machine drives the impeller to rotate in the cylindrical casing, and the gas enters from the current collector, obtains energy through the impeller, increases the pressure and speed, and then discharges in the axial direction. The axial flow fan is arranged in three types: vertical, horizontal and inclined. The small impeller has a diameter of only about 100 mm and a large one can reach more than 20 meters.
The small low-pressure axial flow fan is composed of impeller, casing and current collector, and is usually installed on the wall or ceiling of the building. The large high-pressure axial flow fan is composed of current collector, impeller, streamline body, casing and diffusion cylinder. And the transmission components. The blades are evenly arranged on the hub, and the number is generally 2-24. The more blades, the higher the wind pressure; the blade installation angle is generally 10 ° ~ 45 °, the larger the installation angle, the greater the air volume and wind pressure. The main parts of the axial flow fan are mostly welded or riveted with steel plates.
Diagonal flow fan
An oblique flow fan is also called a mixed flow fan. In this type of fan, the gas enters the impeller at an angle to the axis, gains energy in the blade path, and flows out in an oblique direction. The impeller and the casing of the ventilator are conical in shape. This ventilator combines both centrifugal and axial flow characteristics with a range of flow rates and efficiencies.
Cross flow fan
The cross flow fan is a small high pressure centrifugal fan with a forward multi-blade impeller. The gas enters the impeller from one side of the outer edge of the rotor and then exits the interior of the impeller from the other side. The gas is subjected to the force of the blade twice in the impeller. It has a small size and low speed under the same performance conditions.
Cross flow fans have higher efficiency than other types of low speed fans. Its axial width can be arbitrarily chosen without affecting the flow state of the gas, and the gas remains evenly distributed throughout the width of the rotor. Its outlet section is narrow and long and is suitable for installation in a variety of flat equipment for cooling or ventilation.
The performance parameters of the ventilator mainly include flow, pressure, power, efficiency and speed. In addition, the size of noise and vibration is also the main technical indicator of the ventilator. The flow rate is also called the air volume, expressed as the volume of gas flowing through the fan per unit time; the pressure is also called the wind pressure, which refers to the pressure rise value of the gas in the fan, which has static pressure, dynamic pressure and full pressure; the power is Refers to the input power of the fan, ie the shaft power. The ratio of the effective power of the ventilator to the shaft power is called efficiency. The ventilator has a full pressure efficiency of up to 90%.
The future development of the ventilator will further improve the aerodynamic efficiency, device efficiency and efficiency of the ventilator to reduce power consumption; replace the large centrifugal ventilator with an axial flow fan with adjustable blade; reduce the noise of the ventilator; Wear resistance of the impeller and casing of the dust exhaust fan; realize variable speed regulation and automatic adjustment.
Classified by pressure
1. Low-pressure centrifugal fan: The fan inlet is a standard atmospheric condition, and the fan is full-pressure centrifugal fan with PtF≤1kPa.
2. Medium pressure centrifugal fan: The fan inlet is the standard atmospheric condition, and the total pressure of the fan is 1kPa.
3. High-pressure centrifugal fan: The fan inlet is the standard atmospheric condition, and the total pressure of the fan is 3kPa.
4. Low-pressure shaft flow fan: The fan inlet is the standard atmospheric condition, and the full pressure of the fan is the axial flow fan with PtF≤0.5kPa.
5. High-pressure shaft flow fan: the fan inlet is the standard atmospheric condition, and the total pressure of the fan is 0.5kPa.
Classified by size
Specific speed refers to the speed required to reach unit flow and pressure.
Low specific speed fan (ns=11~30) 2. Medium specific speed fan (ns=30~60) 3. High specific speed fan (ns=60~81)
Classified by purpose
According to the purpose of the fan, it can be divided into induced draft fan, textile fan, fire exhaust fan. The purpose of the ventilator is generally represented by the Chinese pinyin prefix.
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Standards:
DIN 17223-1 Round Steel Wire for springs
DIN EN 10270-1 Steel Wire for Mechanical Springs
GB 3206-82 Carbon Constructional Quality Steel Wire
JIS G 3521-1991 Hard Drawn Steel Wire
GB 4357-89 Carbon Spring Steel Wire
YB/T 5220-93 Carbon Steel Wire For Non-Mechanical Springs
YB/T 5032-2006 Mild Steel Wire for Important Purposes.
ASTM A853-04 Standard Specification for steel wire, carbon, for General Use.
ASTM A227 Steel Wire, Cold-Drawn For Mechanical Springs
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