Ventilator is a mechanical energy, which can improve the gas pressure side by side, and it is a driven fluid machinery.

Fan widely used in factories, mines, tunnels, cooling towers, vehicles, ships and buildings ventilation, row dust and cooling; industrial boilers and furnaces and ventilation fan; air conditioning equipment and household appliances in the cooling and ventilation; grain drying and sending; wind tunnel wind source and the hovercraft inflated and propulsion.

Ventilation machine working principle and turbine compressor are basically the same, just because of the low gas flow rate, pressure has little change, generally do not need to consider changes in the specific volume of gas, namely the gas as incompressible fluid handling.

Fan has a long history. China in BC for many years has created a simple wooden hulling windmill. It is the role of the principle and the modern centrifugal ventilation machine is basically the same. In 1862, Britain's Goebel invention centrifugal fan, the impeller, the casing is a concentric circle type, chassis with brick, wooden impeller with straight blades, efficiency of only is about 40%, mainly for mine ventilation. In 1880, the design people out for mine supply and exhaust volute casing of a wind, and to the curved blade centrifugal fan, the structure is more perfect.

In 1892 the French development into a crossflow fan; in 1898, Irish design before to the blade of the San Siro Ke centrifugal ventilation machine, and for all countries widely used; in the 19th century, axial flow fan has been applied in mine ventilation and metallurgy blast, but the pressure is only 100 to 300 PA, efficiency is only 15 ~ 25%, until the 20th century, 40 years later to get rapid development.

In 1935, Germany, the axial pressure fan for boiler ventilation and air draught. In 1948, Denmark made in the operation of the rotor blade adjustable axial flow fan; rotating axial flow fan, radial acceleration axial flow fan, oblique flow fan and cross flow fan also won the development.

According to the direction of gas flow, the ventilation machine can be divided into centrifugal, axial flow, oblique flow and cross flow type and so on.

Centrifugal ventilation machine, power machine (motor) drive impeller in the volute casing rotate, the air through the suction port from the center of the impeller suction. The gas pressure and speed can be improved due to the dynamic effect of the blade to the gas. Because the flow of gas in the impeller is mainly in the radial plane, it is also known as the diameter of the wind turbine.

The centrifugal fan is mainly composed of the impeller and the casing, and the impeller of the small fan is directly mounted on the motor and the large fan is connected with the motor through the coupling or the belt wheel. Centrifugal fan is generally unilateral air inlet, single-stage impeller; flow of dual inlet, impeller using two back-to-back, also known as double suction centrifugal fan.

The impeller is the main part of the fan, its geometry, size, number of blades and manufacturing accuracy have a great influence on the performance. The impeller by the static or dynamic balance correction to ensure the fan turning smoothly. According to the different direction of blade outlet, the impeller is divided into three types: forward, radial and backward. Prior to the impeller blades at the top of the direction of rotation of the impeller to tilt; the radial impeller blade tip is to radial, straight blade and curved blade; after to impeller blade tip to the reverse direction of the rotation of the impeller tilt.

Prior to the impeller produces maximum pressure in the flow and speed is certain, the diameter of the impeller is the smallest, but the efficiency is generally low; after contrary to the impeller, pressure generated by the minimum required the largest diameter impeller, and efficiency is generally higher; radial impeller somewhere in between. The blade profile is the most simple and the wing type blade is the most complex.

In order to make the surface of the blade have a suitable velocity distribution, it is generally used to make a curved blade, such as the thickness of the blade. The impeller usually has a cover plate, in order to increase the strength of the impeller and reduce the gas leakage between the blades and the casing. The blade and cover plate are connected by welding or riveting. The weight of the welding impeller is lighter, the flow channel is smooth. Low, medium pressure centrifugal fan impeller also use aluminum alloy casting.

Axial flow type ventilator work, engine driven impeller in the cylindrical casing rotation, the gas from the collector into and through the impeller gain energy, increase the pressure and speed, and then along the axial discharge. Axial flow fan's layout has three kinds of vertical, horizontal and inclined type, the small diameter of the impeller is only about 100 mm, the size of up to 20 meters or more.

Small low-pressure axial flow fan consists of impeller, casing and current collector and other parts, is usually installed in the building walls or ceilings; large high pressure shaft flow fan is composed by the collector, impeller, streamline body, chassis and diffusion tube, and the transmission member. The blade is arranged on the hub, the number is generally 2 ~ 24. The more leaves, the higher the wind pressure, the installation angle of the blade is generally 10 to 45 degrees, the greater the installation angle, the greater the air flow and the air pressure. The main parts of axial flow fan are welded by steel plate or by riveting.

The fan is also called mixed flow fan. In this type of fan, the gas enters the impeller in a certain angle with the axis of the shaft, and the energy is obtained by Ye Daozhong in the direction of the flow. The shape of the impeller and the casing of the ventilator is conical. This kind of fan has the characteristics of both centrifugal and axial flow, the flow range and the efficiency are all in between the two.

The cross flow fan is a small high pressure centrifugal fan with forward multi wing impeller. Gas from one side of the outer edge of the rotor into the impeller, and then through the impeller is discharged from the other side, gas in the impeller twice by the role of leaf. Under the same conditions, its size is small and the speed is low.

Compared with other types of low speed fan, cross flow fan has higher efficiency. Its axial width can be arbitrarily chosen, but does not affect the flow of gas, gas flow in the entire rotor width is still maintained. Its exit section is narrow and long, suitable for cooling or ventilation in a variety of flat shaped devices.

The performance parameters of the ventilator are flow, pressure, power, efficiency and speed. In addition, the noise and vibration of the main technical indicators of the ventilator. Also known as the air volume flow, in unit time through the ventilator, the gas volume is said, also known as the wind pressure is a gas in the ventilation machine pressure value, static pressure, dynamic pressure and total pressure; power is refers to the input power of the fan, the shaft power. The ratio of effective power and shaft power of the ventilator is called efficiency. The full pressure efficiency of the fan is 90%.

Fan future development will further enhance the gas fan aerodynamic efficiency and system efficiency and use efficiency, to reduce the consumption of electricity; rotor blade adjustable axial flow fan instead of large centrifugal fan; fan noise reduction; improve the exhaust gas, row dust fan impeller and casing wear resistance; variable speed regulation and automatic regulation can be realized.