Axial-flow Fans

Axial-flow fans are the familiar propeller-type fan (similar in many ways to residential fans that get plugged into the wall for space cooling); the air is passed straight through. Axial fans are often directly connected to their motors, avoiding losses associated with a drive belt. They also have a central hub that allows the motor to fit neatly behind the fan with little penalty in efficiency. Axial fans can be subdivided into three categories (see Figure 1): propeller fans (used to move high air volume against low or no static pressure), tube-axial fans (fans that encase the propeller in a duct section), and vane-axial fans (fans that use straightening fins to convert circular, twisting air to get the fan moving). Vane-axial fans tend to be the most efficient fans available for HVAC air-handling units—with efficiencies in the high 80s—largely because the direction of the airflow is little changed as it passes through the fan.

Figure 1 : Types of axial fans

	Type 1: The Propeller Type 2: The tube-axial Type 3: The vane-axial.
Source: Modern Heating, Ventilating, and Air Conditioning