A device that transfers energy to a continuously flowing fluid by the dynamic action of the blades on the rotating impeller or drives the blades to rotate by the energy transmitted by the fluid is called an impeller machine. In an impeller machine, the rotating blades do positive or negative work on the fluid, causing the pressure of the fluid to increase or decrease. Impeller machines are divided into two categories: one is the working machine, from which the fluid absorbs power to increase the pressure head or water head, such as vane pumps and ventilators; the other is the prime mover, in which the fluid expands, reduces the pressure or water head to generate power, such as steam turbines and water turbines. People call the prime mover a turbine, and the working machine a blade fluid machine.
According to the working principle of the fan, it is divided into two categories: blade type and volume type, among which the blade type can be divided into axial flow type, centrifugal type and mixed flow type. According to the pressure generated by the fan, it can be divided into blowers, compressors and ventilators. my country's current machinery industry standard JB/T2977-92 stipulates that: a ventilator refers to a fan with an outlet pressure (gauge pressure) less than 0.015MPa under standard air inlet conditions; a blower with an outlet pressure (gauge pressure) between 0.015MPa and 0.2MPa; a compressor with an outlet pressure (gauge pressure) greater than 0.2MPa.
The main components of a blower are: volute, collector and impeller.
The collector can guide the gas to the impeller, and the airflow condition at the impeller inlet is guaranteed by the geometric shape of the collector. There are many shapes of collectors, mainly: cylindrical, conical, cylindrical cone, arc, cylindrical arc, arc cone, etc.
The impeller generally consists of four major components: wheel cover, wheel disc, blades, and shaft disc. The main connection methods of its structure are welding and riveting. According to the different installation angles of the impeller outlet, it can be divided into three types: radial, forward and backward. The impeller is the most important part of the centrifugal fan. It is driven by the prime mover and is the heart of the centrifugal impeller machine. It is responsible for the energy transfer process described by the Euler equation. The flow inside the centrifugal impeller is affected by the rotation of the impeller and the curvature of the surface, and is also accompanied by flow separation, backflow and secondary flow, which makes the flow inside the impeller very complicated. The flow condition inside the impeller directly affects the aerodynamic performance and efficiency of the entire stage and even the entire machine.
The volute is mainly used to collect the gas coming out of the impeller. At the same time, it can convert the kinetic energy of the gas into the static pressure energy of the gas by moderately reducing the gas velocity, and guide the gas to leave the volute outlet. As a fluid impeller machine, it is a very effective method to improve the performance and work efficiency of the blower by studying its internal flow field. In order to understand the real flow conditions inside the centrifugal blower, improve the impeller design and volute design to improve performance and efficiency, scholars have done a lot of basic theoretical analysis, experimental research and numerical simulation calculations on centrifugal impellers and volutes.
Other structures of the blower:
- Rotor: It consists of a shaft, an impeller, a bearing, a synchronous gear, a coupling, a sleeve, etc.
- Bearing: The 3000 double-row radial spherical roller bearing is used as the positioning end near the coupling end. The 32000 single-row radial short cylindrical roller bearing is used as the free end near the gear end to adapt to the axial displacement of the rotor during thermal expansion.
- Synchronous gear: It consists of a gear ring and a hub, which is convenient for adjusting the impeller clearance.
- Body: It consists of a casing and left and right wall panels. The left and right wall panels and the bearing seats and seals installed in the left and right wall panels can be used interchangeably.
- Base: Medium and small fans are equipped with a common base, and large fans are only equipped with a fan base for easy installation and commissioning.
- Lubrication: The gears are immersed and the bearings are splash lubricated. The lubrication effect is good, safe and reliable.
- Transmission mode: It is mainly based on direct coupling. If the performance specifications require, the V-belt pulley speed change method can also be used. The coupling uses an elastic coupling, which can mitigate the impact and compensate for a small amount of axis deviation. In addition to electric motors as driving machines, large-flow fans can also use steam turbines or other driving machines.
