Types of Drives
Three main types of fans:
Axial Fans
Axial Fans
- Low Pressure / High Volume
- Axial fans are efficient high volume low pressure machines. These fans are good for general purposes: avionics/electric or personnel cooling; AC and ECS systems, especially if a fan is needed to move air through a heat ex-changer.
These fans are also ideal for scavenging as the parts that come in contact with the air/sand mixture are more easily hardened than the complex shapes of other types of fans. - Axial fans come in two types, Vane-axial and Tube-Axial. Vane-axial fans differ from Tube-Axial’s as they have stationary vanes, sometimes called straightening vanes as they “straighten” the air outlet by counteracting the rotational angle from the turning impeller blades.
These vanes allow a higher pressure capability and add efficiency.
Centrifugal Fans
Centrifugal Fans
- High Pressure / Low Volume
- Centrifugal Fans, also called Blowers are used for high pressure, lower flow applications such as NBC and other types of filtration. They are also used for low pressure lower flow general purpose applications as they can be made inexpensively by simple plastic and aluminum parts.
- Centrifugal Fans are also used for AC systems where there is very long ducting that adds up to a lot of pressure drop.
- Because the moving parts are covered by the scroll or housing, centrifugal blowers tend to be quieter than other types.
Mixed Flow Fans
Mixed Fans
- Medium Pressure / Volume
- High Efficiency / Low Noise
- Mixed Flow Fansare called mixed as they are a sort of combination axial and centrifugal fan. They are basically Vane-axial fans, but the impeller is shaped like a bevel gear, where the fan blades are at an angle. This means the air is moved by a combination of aero-dynamic/mechanical pushing of air, and the centrifugal action of spinning the air against the housing.
In a blower, the housing is called a scroll, and in the mixed flow, the housing is called a shroud. - Mixed flows are usually made for NBC, or other critical applications for a specific design point where high efficiency and lower noise is required as these tend to be more expensive given their complex design. Mixed-flow fans tend to be quieter than other types because of their efficiency and that their moving parts are partially blocked by the shroud.
