AXIAL FAN TYPES
You'll want to consider these fan types if you're looking for a compact, duct installed solution.
In this video, James Mathis covers Axial Fan Fundamentals.
Axial fans are used to move high amounts of airflow at a low pressure.These fans get their name from the way they move air axially, or, in a straight line through the fan. Some common applications are:
- General Ventilation
- Smoke or Fume Removal
- Drying
- Cooling
Some of the most common types of axial fans are Vaneaxial, Tubeaxial, and Duct fans, which are designed to be installed in ductwork, and propeller fans, which are often installed through a wall to the outside. These categories vary by their wheel and housing designs, and performance characteristics.
Performance curves for axial fans have a have a non-overloading horsepower characteristic, meaning power consumption peaks and starts to drop off toward the wide open point of the curve.
Axial fan curves also have a stall region located around the middle of the curve, where performance is unstable.
Axial fans are available in both belt drive and direct drive configurations. With most axial fan types being installed directly into ductwork, direct drive configurations place the motor directly in the airstream, so considerations should be made to ensure a motor can handle airstream conditions when specifying direct drive.
Independent from an axial fan’s size or operating speed, there are a couple other factors that determine its pressure and flow characteristics. One of these factors is the wheel’s hub-to-tip ratio.
Relative to the overall diameter of an axial fan’s wheel, the larger the hub is, the more pressure the wheel will generate. Conversely, the longer the blades are, the more volume of air the wheel will be able to move. In other words, the smaller the hub is, the less pressure it generates. And the shorter the blades are, the less air they move.
Blade angle is another factor that determines an axial fan’s performance characteristics. Increasing a wheel’s blade angle increases pressure and flow. But with the increased performance comes greater power consumption, and lower efficiency. Some axial fans are designed with the blades permanently set at the designed angle. This type is referred to as fixed pitch. Fans can also be designed with Adjustable pitch blades, where blade angle can be adjusted to change performance. Blade angle adjustments are often made manually, but can also be designed to adjust pitch pneumatically while the fan is in operation.
