An Axial Fan, or axial flow fan are simply fans that are designed to move air axially, that is, parallel to the shaft. Axial fans are the most common type of fan, and the one we are are most familiar with. They are often referred to as propeller fans because they closely resemble the propeller on a boat or an aeroplane.
Simple Fans
Axial fans are the most common type mechanical fan that Custom Fans of Australia designs, but certainly not the only type. They are perhaps the simplest, which is how they came to be so common. The earliest type of mechanical fan was the Punkha fan. The Punkha was simply a canvas covered frame attached to a hinge and mounted on the ceiling of a room. A servant, or pair of servants, would pull on a rope attached to the Punkha, which moved it back and forth, thus creating an air flow.
The Punkha was simply a large version of the hand fan which has been used for personal cooling since prehistoric times. At some point it was noticed that if a hand fan was held at an angle and moved through the air, it would move the air for as long as the fan was moving. The best way to keep the individual fan moving was to mount it perpendicular to a shaft, and then rotate the shaft. To help balance the rotating shaft, multiple blades could be attached. There you have it; you have just invented the axial fan.
Axial Fan Performance Factors
The performance of a mechanical fan is measured several ways, the two most important being the amount or volume of airflow, and the speed of airflow. Some users ask about the pressure a fan creates, but pressure is a difficult concept. In fluid dynamics we study the flow of fluid, expressed as the amount of fluid being moved. Amount of flow should not be confused with pressure, because pressure is the resistance to flow.
The most obvious ways to increase the performance of an axial fan is to increase the size of the blades, to increase their pitch or the angle which they move through the air, and by increasing their speed. Increasing the size of the blades increases performance because the longer leading edges of the blades will come in contact with more air. Increasing the pitch or angle of the blade means that the air that comes in contact with the face of the blade will be moved further. The simplest ways to increase the fan’s speed of rotation is to attach a more powerful motor motor or to add a speed-increasing gear train.
More Effective Axial Fans
These methods are effective, but will all run into a common problem. The intent of the axial fan is to move air parallel to the shaft, but as speed and pitch of the blades increase, air begins to slide off the tips of the blades, away from the shaft. The solution is to place the fan inside a shroud or tube. The air moving efficiency of the fan increases tremendously with the use of a shroud because air is not allowed to move in any direction but the one intended–parallel to the shaft.
The fan in a shroud arrangement is sometimes referred to as a tube-axial fan, and they are highly efficient for the sized motor attached. This is the sort of fan used in most electronics cooling applications. Tube axial fans are also used by first responders for de-smoking structures after a fire.