Types of Fans

It is common to classify fans in

• Axial and/or propeller fans
• Centrifugal (radial) fans
• Mixed flow fans
• Cross flow fans

The pressure head of different types of fans with equal periphery speed of the wheel are compared in the capacity diagram below:

Centrifugal fans with forwarded blades are suited for application with higher air flow volumes and pressures. Axial propeller fans are more suited for applications with lower volumes and pressures.

Axial and Propeller Fans

In an axial fan the air flows in parallel to the shaft. It is common to classify axial fans upon their wheel like:

• C-wheel - Blades can be adjusted when running. High efficiency, small dimensions, variable air volume
• A-wheel - Blades can be adjusted only when the fan is standing still. High efficiency, small dimensions, adaptive to recommended air volume
• K-wheel - Blades can not be adjusted. Simple, small dimensions

The pressure head developed for single stage is up to 300 N/m². Axial fans are suited for relatively large volumes compared to pressure.

Centrifugal fans (Radial fans)

In a centrifugal fan the air flows is in a radial direction relative to the shaft. Centrifugal fans can be classified by their wheel like:

• F-wheel - Curved forward blades. High efficiency, small dimensions, changing in pressure have little influence on pressure head.
• B-wheel - Curved backward blades. High efficiency, low energy consumption, changing in pressure have little influence on air volume. Low noise emission, stable in parallel running.
• P-wheel - Straight backward blades. High efficiency, self cleaning, changing in pressure have little influence on air volume
• T-wheel - Straight radial blades. Self cleaning. Suitable for material transport

Types of blades used in centrifugal fans are

• Straight steel plate paddle wheel
• Forward multi-vane multi-blade
• Backward turbo-vane

The different blades can be characterized as shown in the capacity diagram below:

Mixed flow fans

In a mixed flow fan the air flows in both axial and radial direction relative to the shaft. Mixed flow fans develops higher pressures than axial fans.

Cross-flow fans

In a cross flow fan the air flows in an inward direction and then in an outward radial direction.