Fans are designed to bow air either parallel to the fan shaft which is referred to as axial cooling and at right angles to the fan shaft. A centrifugal air blower is one in which the air flow is perpendicular or at right angles to the fan shaft. Axial fans are ideal for moving large volumes of air and are commonly used in the home, centrifugal fans on the other hand are better suited in applications where the demand is not volume but higher air pressure. As these fans are used in high pressure applications they are popular in industrial processes and large air pollution control installations.
A centrifugal fan consists of the fan wheel, the housing in which the wheel sits, the drive mechanism and dampers either on the inlet, the outlet or both. The fan wheel is made from a series of blades which are fitted to a central hub which rides on a shaft. The shaft passes through the housing and is supported on bearings. Air comes into the fan through the center of the wheel and then turns a full 90 degrees to pass over the blades and exit the housing.
The drive mechanism is usually direct drive, belt drive or variable speed drive. The drive mechanism design is that which determines the speed of rotation of the fan wheel and how much the speed can vary, if any. A direct drive mechanism is where the fan shaft is coupled directly to the shaft of the drive motor, in this case the coupling is flexible and as the drive is direct, the speed of the motor is also the speed of the blade with no possible variable. A belt drive uses one or more belts which run over sheaves which are attached to the drive motor and to the fan shaft. Depending on the diameters of the sheaves, the fan blade speed is determined. A variable speed centrifugal air blower uses hydraulic drives or magnetic couplings.
A centrifugal air blower can be used for many industrial processes because they can increase the air pressure considerably. One can often see them installed in grain drying facilities, greenhouse ventilation and more. They are commonly used in HVAC as well as air pollution control systems.
