Differences Between Mixed Flow Fan and Centrifugal Fan: Technical Comparison and Application Guidance

Mixed flow and centrifugal fans are both common in industrial and commercial ventilation. A mixed flow fan blends axial and radial flow: air enters nearly parallel to the shaft but exits with a radial component. In contrast, a centrifugal fan pulls air in axially and forces it out perpendicular to the shaft. These differences manifest in their impeller geometry, flow characteristics, and performance curves. For example, European regulations define axial fans as having a flow-angle ≤20°, centrifugal ≥70°, and mixed flow in between. This means a mixed flow impeller is literally a “hybrid (centrifugal and axial) wheel”. In practice, mixed flow fan often features a streamlined inlet funnel and fewer, twisted blades, whereas centrifugal blower uses a scroll housing and multi-bladed wheels (forward-curved, backward-curved, backward-inclined, etc.).

                  

Mixed Flow Fan 3D modeling                                                                     Centrifugal fan 3D modeling

• Impeller and Flow Path: Mixed flow fan draws air axially but impart a diagonal component, so the discharge is partly axial and partly radial. Centrifugal fan discharges air purely radially. For example, one fan manufacturer notes that centrifugal wheels “enter parallel to and then are discharged perpendicular to the axis”, giving very high pressure, whereas mixed flow wheels “move air at an angle to the axis” for medium pressure. The fan flow-angle classification confirms this: mixed flow is defined by 20–70° outlet angle.

• Pressure–Flow Curve Behavior: Mixed flow fan usually exhibits a non-overloading power curve and is relatively stall-free. It can handle system fluctuations without surging or stalling. Centrifugal fan also can be made non-overloading (especially backward-inclined types), but some designs (forward-curved wheels) will show rising pressure and power as flow drops (“overload”). In general, mixed flow fan has smoother, more linear pressure–flow curves, whereas centrifugal fan often attains higher peak pressures at lower flows.

• Dimensional Footprint: Because mixed flow fans are essentially inline units, they tend to be more compact. One manufacturer notes that mixed flow/inline fans “provide the performance of a centrifugal fan with the space-saving advantages of an axial type fan”. A mixed flow fan can often replace a small centrifugal blower in tight ductwork. Centrifugal fans, by contrast, require a heavier housing (volute or scroll), drive bearings, and often a baseplate, making their overall footprint and weight larger for a given air volume.

• Energy Efficiency: Both fan types can be efficient if well-designed. In fact, tests show that a mixed flow impeller can exceed the efficiency of a similar-size centrifugal blower. Many mixed flow fans achieve moderate static efficiencies (45–55%) and run quietly. High-end centrifugal fans (e.g. backward-curved or airfoil wheels) can reach 70–90% efficiency. In partial-load or variable-speed operation, both fan types can be paired with VFDs. Backward-curved centrifugal fans typically maintain good efficiency over a broad flow range.

• Acoustic Performance: Mixed flow fans tend to run quieter. One manufacturer explicitly states that mixed flow fans “operate at lower sound levels” than comparable blowers. Their integrated housing and lower tip speeds reduce noise. Centrifugal fans can also be quiet (especially when fitted with silencer ducts or acoustic enclosures), but they generally require more acoustic treatment. In high-pressure applications, the enclosed scroll of a centrifugal fan helps damp noise, but the higher blade loading can produce more tonal noise.

• Stall and Surge: Mixed flow fans generally have gentle stall behavior. One manufacturer notes they have a “non-overloading” response and resist stalling under variable loads. Centrifugal fans (especially backward-curved) similarly do not surge easily at high resistance; forward-curved designs, however, can overspeed under low flow if not properly controlled. In critical applications, anti-stall features (guide vanes or variable pitch) are often built in.

• Construction and Durability: Centrifugal fans are the workhorses for harsh environments. They are commonly built from heavy-gauge steel or stainless, with robust bearings and can be fitted with heat- or corrosion-resistant components. Mixed flow fans can also be ruggedized: for example, industrial mixed flow units often use thick stainless cases and alloy blades with spark-arresting features. However, in extremely dirty, abrasive, or high-temperature streams, a centrifugal blower (especially backward-inclined or airfoil wheel) is usually preferred for its larger blade-to-wall clearances and sturdier housing.

Fan Testing Standards: Both fan types are rated under the same laboratory standards. ANSI/AMCA 210 (ANSI/ASHRAE 51) and ISO 5801 define uniform airflow test conditions so that performance data (CFM, static pressure, power, efficiency) are comparable. These standards specify inlet/outlet ducts and straighteners to minimize flow disturbances. For thrust fans (like tunnel jets), AMCA 250 sets out thrust testing. In practice, certified ratings will note if ducts were present during the AMCA 210 test. Thus, when comparing fans, engineers must ensure ratings come from the same test configuration.

Performance Comparison

• Static Pressure: Centrifugal fans generate higher pressure rises. Typical centrifugal blowers can achieve static pressures from a few inches of water up to several kPa by using multi-stage wheels or airfoil blades. Mixed flow fans are generally limited to medium pressures (often under 2 kPa), more than axial fans but less than large blowers.

• Airflow Volume: For a given size, mixed flow fans move a large volume with moderate pressure. They often outperform centrifugal fans in maximum flow at low to moderate backpressure. (For very high volumes at very low pressure, axial fans are still best.)

• Energy Efficiency: As noted, mixed flow fans are very efficient for their class. Centrifugal fans can reach higher peak efficiencies but may require more horsepower at low flow. Both types benefit greatly from proper selection near the Best Efficiency Point (BEP). At part-load, efficiency will drop for both; forward-curved blowers tend to drop quicker than backward-curved units.

• Acoustic Noise: Mixed flow fans are praised for quiet operation. Centrifugal fans can be relatively quiet in high-pressure service due to lower blade speeds and ducted housings, but may produce more broadband or tonal noise without silencing. Lab fans or HVAC blowers often use backward-curved impellers specifically for noise control.

• Installation Flexibility: Mixed flow (inline) fans can be mounted in any duct orientation (horizontal or vertical) and even ceiling-suspended, as the motor is often on top of the housing. Their compact shape means fewer interference issues. Centrifugal fans, having a heavy housing and base, need solid supports but can orient inlet/outlet in many directions. Belt-driven centrifugals allow the motor to be placed away from airflow (useful in high heat), whereas many mixed flows are direct-drive.

• Durability and Duty: For industrial duty (dust, humidity, chemicals), rugged centrifugal models dominate. They typically have thick stator housings, sealed bearings, and motors rated for harsh service. Mixed flow fans can be built for heavy duty (stainless steel frames, special coatings), but most are used in cleaner or filtered air streams. In short, both designs can be heavy-duty, but blowers have a longer history in abusive environments.

Applications and Selection Guidance

Choosing between mixed flow fan or centrifugal fan depends on the setting:

• HVAC Rooftop Systems: Roof-mounted exhaust or supply fans (roof fans) often favor high-flow axial or mixed-flow units. Simple propeller roof fans (axial) are used for very low back-pressure systems. When ducts, filters, or louvers add resistance, a mixed flow inline fan or a small centrifugal exhaust fan may be chosen. Mixed flow roof fans combine decent pressure capacity with lower profile and vibration. In very high-buildings with extreme static requirements, plenum (centrifugal) fans or belt-driven blowers might be used.

• Industrial Environments: In factories, kilns, or process plants where air contains contaminants or heat, heavy-duty centrifugal fans are the usual choice. Their large wheels and clearances handle particulates and their construction tolerates high temperatures. Backward-inclined or airfoil centrifugal models (often with explosion-proof motors) are common. Mixed flow fans can be used for industrial ventilation if the air is clean or filtered, especially where a compact unit is needed. Ultimately, the fan selection must match the filter/duct load: for very high-pressure drops, a centrifugal is safer.

• Cleanrooms, Labs, High-Pressure Systems: Critical ventilation (cleanrooms, labs) demands ultra-quiet, stable fans. Mixed flow fans, with their smooth curves, can be beneficial in noise-sensitive clean environments, as long as they meet the static needs. Often, backward-curved centrifugal fans or low-speed inline blowers are chosen for minimal vibration and sound. In high-pressure HVAC systems (tight filters, high-rise AHUs), plenum fans (centrifugal wheels without full housing) or small multi-stage blowers may be used. In short, if the system pressure is moderate (under a few kPa) and space/quietness are priorities, mixed flow is acceptable. For multi-kPa systems (deep filters, long duct runs), centrifugal blowers are safer.

Each application has trade-offs. In general, if compactness and moderate pressure are key, mixed flow fans excel. If maximum pressure or durability is needed, a centrifugal design is usually chosen.

Note: The data is for reference only, please consult relevant companies for details. And the content of the article cannot avoid omissions and errors. Welcome to propose corrections.