Air moving devices are generally described as being either a type of fan (Fig. 1a) or a centrifugal blower (Fig. 1b). The main difference between fans and blowers is in their flow and pressure characteristics. Fans deliver air in an overall direction that is parallel to the fan blade axis and can be designed to deliver a high flow rate, but tend to work against low pressure. Blowers tend to deliver air in a direction that is perpendicular to the blower axis at a relatively low flow rate, but against high pressure.
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| Figure 1 (a): A typical fan | Figure 1 (b): A typical blower |
There are several types of fans, some of the most common being propeller, tube axial and vane axial styles. Propeller fans are the simplest type of fan, consisting of only a motor and propeller. One problem with propeller fans is that tip vortices are produced by the pressure differential across the airfoil section.
A tube axial fan (the most common type in electronic cooling systems) is similar to a propeller fan, but also has a venturi around the propeller to reduce the vortices. The vane axial fan has vanes that trail behind the propeller in the airflow to straighten the swirling flow created as the air is accelerated.
Centrifugal blowers may have a forward curved wheel, a backward curved wheel, or be of the squirrel cage variety.
Information provided by: http://www.electronics-cooling.com