Multi stage centrifugal fan is an industrial power equipment that uses multiple impellers in series to achieve gradual gas pressurization. It is widely used in medium and high pressure scenarios such as boiler blowing, sewage treatment aeration, and chemical pneumatic conveying. Its structure and working principle are based on the mechanism of centrifugal force and kinetic energy pressure energy conversion, and it has the characteristics of high efficiency, stability, and long service life.
Core structure composition
Multi stage impeller: arranged in series along the main shaft, usually made of high-strength alloy steel or aluminum alloy casting, each stage of impeller works independently, and the blade type is mostly backward curved or wing shaped to optimize aerodynamic efficiency.
Refluxor: Located between the outlets of each stage of the impeller, it guides the airflow from radial to axial direction, accurately guiding it into the inlet of the next stage of the impeller, ensuring continuous and stable airflow, and reducing vortex loss.
Diffuser: located behind each stage impeller, it reduces gas flow velocity through a gradually expanding channel, efficiently converts kinetic energy into static pressure energy, and is a key link in pressure increase.
Shell and partition: The overall cast iron or welded steel plate structure is equipped with graded partitions to form independent compression chambers, and the surface is often coated with epoxy resin to enhance corrosion resistance. Some models adopt radial sectioning design for easy maintenance.
Sealing system: Maze seals or carbon ring seals are used between stages and shaft ends to effectively prevent high-pressure gas leakage, ensuring system airtightness and operational efficiency.
Bearings and Spindle: The spindle is made of high rigidity carbon steel or alloy steel, supported by rolling or sliding bearings at both ends to withstand radial and axial loads. Some large fans are equipped with independent oil lubrication and cooling systems.
Silencing device: The intake and exhaust ports are integrated with mufflers to reduce operating noise to below 85dB (A), meeting industrial environmental noise control standards.
Working principle and energy conversion process
Gas enters the first stage impeller axially from the inlet of the fan, and is accelerated and thrown out radially under the centrifugal force of high-speed rotation. At this time, the kinetic energy of the gas is significantly increased. Subsequently, the airflow enters the diffuser, where the cross-sectional area of the flow channel expands, slowing down the airflow and converting kinetic energy into static pressure energy, achieving the first pressure increase.
The gas after expansion changes its flow direction through the reflux device and is reintroduced axially into the inlet of the next stage impeller, repeating the above acceleration expansion process. After completing each stage of compression, the gas pressure accumulates step by step and eventually gathers in the final volute, and is discharged through the outlet.
The pressure increase mainly occurs in the impeller (about 70%), followed by the expansion section (about 30%). The entire process does not rely on drastic changes in gas compression ratio, but rather achieves high-pressure output through multi-stage low-speed (usually 2000-4000r/min) cooperation, avoiding the material fatigue and vibration risks caused by the tens of thousands of revolutions per minute high-speed operation required for single-stage fans.
Technical advantages and design features
High pressure output capability: Single stage fans are limited by speed and material limits, and the maximum pressure is usually below 0.1MPa; The multi-level structure can easily achieve high pressure output of 0.1-0.2MPa, meeting the demanding requirements of industry.
High operational stability: Low speed design reduces bearing wear and vibration, extends equipment life, and can operate continuously for more than 1 year.
Energy efficiency optimization: Through the design of a three element flow meridional impeller and wing shaped reflux device, the aerodynamic efficiency can reach over 78%, and with the help of variable frequency speed regulation, load adaptive energy saving can be achieved.
Modularity and maintainability: The structure adopts a modular series design, which is easy to disassemble and replace single level components, supports online maintenance, and reduces downtime costs.
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