Mixed Flow Fan

Description :

Mixed flow fan is also commonly known as diagonal flow fan, occasionally mistakenly referred to as "rogue fan" in the market. It is a widely used pipeline ventilation equipment in the fields of HVAC, fire protection, and industrial ventilation. Its aerodynamic characteristics are between axial flow fans and centrifugal fans, and the airflow includes both axial propulsion and radial diffusion states, hence the name mixed flow fan. It combines the dual advantages of high air volume and compact size of axial flow fans and high static pressure of centrifugal fans, making up for the shortcomings of both types of fans. It is the preferred equipment for medium resistance ventilation pipelines and is now widely used in various projects such as civil building ventilation, fire smoke exhaust pressurization, chemical anti-corrosion ventilation, explosion-proof exhaust, etc.

From the perspective of working principle, ordinary axial flow fans have direct airflow in and out, relying on the axial thrust of the blades to supply air. The air pressure is relatively low. Once the air duct is long, there are many bends, and filters are installed, the ventilation effect will be greatly reduced; After the airflow of the centrifugal fan enters the body, it needs to turn 90 degrees, relying on centrifugal force to generate high wind pressure. However, under the same air volume, the body is large, occupies more space, and has significant installation limitations. The mixed flow fan adopts a meridian accelerated twisted impeller, and the air smoothly enters the collector along the axis of the fan. After contacting the high-speed rotating blades, it is simultaneously subjected to forward axial thrust and outward centrifugal force. The airflow flows out of the casing at an inclined angle, and the wind pressure is much higher than that of ordinary axial flow fans. The air volume is also better than that of centrifugal fans of the same size, and it is suitable for working conditions with multiple bends, medium duct length, and certain wind resistance. The aerodynamic efficiency can reach 80% to 88%, with lower energy loss and more energy-saving long-term operation.

The overall structure of the mixed flow fan is compact and simple, and the core components are divided into five modules: impeller, cylindrical casing, motor, collector, and guide vane. The impeller is the core that determines the performance of the fan, and generally uses 4-8 twisted wide blades. The materials are divided into four types: carbon steel paint, aluminum alloy, 304 stainless steel, and fiberglass. All of them have undergone G2.5 dynamic balance correction, effectively reducing operating vibration and noise. The cylindrical straight through casing does not require the bulky volute of a centrifugal fan, and can be directly connected to a circular ventilation duct. It is equipped with a streamlined current collector and outlet guide plate inside to regulate the turbulent airflow and reduce wind resistance losses. The main driving method is direct motor connection, without easily worn accessories such as belts and bearing seats, resulting in a low failure rate; Some anti-corrosion and high-temperature special models adopt an external motor structure, which eliminates the need to disassemble the air duct during motor maintenance, making maintenance more convenient. The supporting accessories include shock-absorbing base, canvas soft joint, rainproof hood, muffler, and variable frequency controller, which can be purchased according to on-site needs.

Compared to traditional fans, mixed flow fans have outstanding comprehensive advantages. Firstly, the performance balance has a wide range of adaptability, with a conventional wind pressure range of 150-1200Pa and an air volume coverage of 3000-96000m ³/h. It can meet the ventilation needs of large spaces and overcome the wind resistance caused by air ducts, noise reduction, and filtration equipment. Secondly, the installation method is flexible. The cylindrical pipeline design supports horizontal lifting, vertical landing, and vertical pipe well installation, occupying only half the area of centrifugal fans with the same parameters. It is suitable for limited space scenarios such as computer rooms, underground garages, and narrow pipe wells. Thirdly, the operating noise is lower, with standard models maintaining a normal operating noise level of 70-75 decibels, meeting the noise requirements of places such as shopping malls, office buildings, and residential basements. Fourthly, the product series is complete, and different types of protection can be customized according to the environment. It includes ordinary ventilation, dual speed dual-use, fire high temperature, anti-corrosion fiberglass, and explosion-proof models, which can adapt to various complex working conditions such as room temperature, high temperature, acid and alkali corrosion, flammability and explosiveness.

According to their functions and usage environments, mixed flow fans are mainly divided into five mainstream series. One of them is the SWF low-noise ordinary mixed flow fan, which is commonly used for daily ventilation and air exchange in shopping malls, office buildings, and underground computer rooms. The medium temperature does not exceed 60 ℃, making it the most cost-effective. The second is the HLF dual speed mixed flow fan, which has two speeds: high and low. The low speed is used for daily ventilation and air exchange, while the high speed meets the needs of fire smoke exhaust and emergency ventilation. One device can achieve two functions, saving equipment procurement and installation costs. The third one is the HTF high-temperature mixed flow fan for fire protection, a specialized model for building fire protection. It can operate continuously and stably for 30 minutes in a high temperature environment of 280 ℃. It is mainly used for smoke exhaust in underground garages, positive pressure air supply in stairwells and elevator lobbies, and is an essential equipment for fire inspection. The fourth one is FSJG fiberglass anti-corrosion mixed flow fan, which is made of FRP fiberglass integrated molding, acid and alkali resistant, and moisture resistant. It is suitable for corrosive waste gas emission scenarios such as sewage stations, electroplating workshops, acid pickling plants, and waste gas spray towers. The fifth one is FBSJG explosion-proof mixed flow fan, equipped with explosion-proof Ex explosion-proof motor. The body has no risk of spark generation and is used in flammable and explosive places such as paint spraying rooms, chemical warehouses, biogas collection workshops, etc.

The application scenarios of mixed flow fans cover two major sectors: civil buildings and industrial production. Building fire protection is its core application area, and the smoke control and exhaust systems of high-rise residential buildings, commercial complexes, and underground parking lots are basically equipped with fire mixed flow fans to ensure rapid smoke discharge and pressurized smoke control in evacuation routes during a fire. In civil ventilation scenarios, hotels, supermarkets, and office buildings rely on mixed flow fans to complete indoor air circulation and basement dehumidification and exhaust. The industrial sector has more diverse applications, with ordinary carbon steel models used for conventional ventilation in factories; FRP anti-corrosion machine for treating chemical acidic and alkaline waste gases; Explosion proof models complete the exhaust of paint and volatile gas workshops; Small and medium-sized mixed flow fans can also be used for local ventilation in tunnels, ventilation in breeding farms, heat dissipation in equipment rooms, and supporting air supply for environmental protection spray towers.

The selection, standardized installation, and regular maintenance of fans directly determine the service life and operational effectiveness of the equipment. When selecting, it is necessary to first calculate the required air volume on site and the total resistance of the pipeline. A 10% margin should be reserved for air volume to deal with air leakage in the air duct. When there are many air duct bends, filters, and mufflers, high pressure models should be prioritized; According to the temperature, corrosiveness, and flammable and explosive properties of the medium, match the corresponding materials and motor protection levels, and distinguish the machine number according to the impeller diameter, covering all conventional engineering requirements from No. 2.5 to No. 10. During the installation phase, the base must be equipped with rubber shock absorbers, and the inlet and outlet of the fan must be connected with fireproof canvas soft joints to block vibration transmission and reduce noise; The equipment installation should be kept level and firm. For outdoor installation, a rainproof wind cap should be installed. The motor junction box should be well sealed for waterproofing. Before powering on, manually turn the wheel to check that there is no shell friction on the impeller, and confirm that the steering is correct before formal operation. The daily maintenance process is simple. In ordinary environments, the surface area of the impeller is cleaned of dust every month. Dust and corrosion conditions are reduced to once every half month to prevent dust accumulation from causing impeller imbalance and increased vibration; Quarterly testing of motor operating current, bearing temperature, and tightening of machine body fixing bolts; Explosion proof and fiberglass anti-corrosion models require additional inspection of the motor's explosion-proof seal and shell for cracking and damage to eliminate safety hazards.

Overall, mixed flow fans solve the limitations of using single axial and centrifugal fans. With balanced aerodynamic performance, compact body, diverse protective styles, and low maintenance costs, they have become one of the most versatile equipment in ventilation engineering. Whether it's new building fire protection facilities or factory waste gas treatment renovation, mixed flow fans can provide stable and reliable ventilation solutions, occupying an irreplaceable position in the HVAC, fire protection, and environmental protection industries. They are also the core main models for ventilation equipment dealers to stock up and purchase engineering.

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