An industrial fan is a turning machine that transmits energy to the fluid (mostly gaseous fluids) by increasing pressure. Industrial fans are classified into two main categories based on the direction of flow of fluid along the direction of vanes or blades of a fan. If the flow is along the direction of radius of vanes, they are called as centrifugal fans. Similarly if the direction of fluid flow is along the direction of axis of vanes then they are called as axial fans. These two types of industrial fans are again categorized into different types.
There are three types of axial fans. They are
- In this type of axial fan two or more single thickness blades are present on the wheel. These fans are low efficient and are generally used in low pressure applications.
- As the pressure produced is low, the amount of volume generated is high for this type and they are used in high volume air moving applications such as air circulation or in a ventilation trough.
- Tube axial is similar to propeller type axial fan, but contains more number of blades on the wheel which increases efficiency and pressure rate of the system.
- These type of axial fans are used in applications where downstream air distribution is not critical. Some industrial applications are drying ovens, paint spray booths and fume exhausts.
- Vane-axial fans use straight vanes to improve efficiency and pressure capability. They usually have airfoil shapes. Pressure rates are from medium to high.
- Used in industrial application where a uniform downstream air distribution is required.
There are six types of centrifugal fans. They are
- Forward curved
- In forward curved type small blades are curved in direction of wheel rotation. The velocity of the fans are relatively less. The wheel type used in this fan is often called as squirrel cage wheel.
- As it produces less pressure, they are used in low pressure applications like domestic furnaces, central station units and packaged air conditioning etc.
- Radial blade
- In radial blade type the blades are perpendicular to the direction of wheel rotation. The wheel is a paddle type wheel which may or may not contain side rims. Produces low pressure and moves relatively a higher mass or volume of fluid.
- Radial blade type find its usage in material handling applications and some moderate pressure industrial applications.
- Backward inclined
- In backward inclined type the blades are flat and move away from the direction of wheel rotation. It produces relatively high speed to move a given amount of air. It is found to be more efficient than the previous type of centrifugal fans.
- As the amount of pressure produced is high, they are used in applications like heating, ventilating and air conditioning systems.
- Airfoil blade
- Airfoil blade is an improvement for backward inclined wheel design. It produces highest amount of efficiency and runs at a slightly higher speed than the backward inclined.
- They are used in HVAC systems and to clean industrial application where energy savings are important.
- Radial tip
- The blades of radial tip are cupped in the direction of the wheel rotation. It has the same velocity as that of a backward inclined wheel to move given mass or volume of air.
- They are used in material handling and unclean applications and is more efficient than the radial blade.
- Inline centrifugal
- This type contains airfoil with backward inclined wheel in a tube-axial casing. The efficiency of this type is less than radial inclined type.
- Used in low pressure return air systems of heating and ventilating. It has a straight through flow of air. It is a combination of a centrifugal and axial type fan.
The amount of air flow and the efficiency of the fan decides the type of fan to be used in an industry. Sometimes a combination of centrifugal fan and axial fan can be used in industrial applications.