Axial fans are one of the categories of fans. They are said to be axial because they allow the fluid to move in the parallel direction to that of the axis of rotation of impeller. While in the other fan categories, i.e. centrifugal and radial fans, the fan pushes the fluid in a direction perpendicular to that of axis of rotation of impeller. Where high flow and lower resistance applications are required, axial fans are best suited. Blade width, number of blades, width of impeller, impeller speed and the angle of cuts on the blades plays an important role in the characteristic performance of axial fans.
The axial fans come in different dimensions, according to their need in the process for which they are being used. For example, the most common type of fan for an air-cooled heat exchanger (ACHE) is less than 14 ft. diameter comprising of 4 blades. For wet cooling towers, a common fan type is a 28 ft diameter comprising of eight blades.
There are different terminologies which are related to fans and must be kept under consideration while studying about axial fans.
Axial flow fans, like the type Custom Fans designs are used where fans are used for localized cooling purposes. In the ventilation systems where there is no large room for larger fans, axial fans are installed to overcome such difficulty. These types of fan are mostly found in small electrical and mechanical gadgets for cooling purposes where there is limited space for fans to be installed. There are different swirls patterns formed when axial fans are allowed to run at different speeds. There can be no swirl, dampened swirl and a full swirl.
To see a picture of axial propeller fans visit this link.