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  Centrifugal Fans & Blowers

    In case of Centrifugal Fans (& Blowers) air  enters the impeller parallel to the axis of rotation. Air then turns in radial direction at the blade inlet of Centrifugal Fan. Air is guided by the rotating blade in radialy outward direction. The momentum provided to the air causes increase in  kinetic and potential energy of air thereby generating air flow and static pressure.

    Air at outlet of Centrifugal fan impeller is at high velocity. The high velocity air discharg is guided by the volute casing. Centriufgal fan volute casing reduces the air velocity converting velocity head to static head. If the high velocity of air comming out of the impeller is not reduced sufficeintly and propely guided it will lead to higher losses.

    There are three types of Centrifugal Fans & Blowers

1. Forward Centrifugal Fan: Blades are curved forward with respect to direction of rotation. Forward curve centrifugal fan design is used for high volume and low pressure application. (upto 2inch of wg) Pressure rise is mostly due to high absolute velocity of air at outlet of impeller. 
2. Backward Centrifugal Fan: Blades are curved backwards with respect to direction of rotation. Backward curve centrifugal fan design is used from low pressure to high pressure application. (2inch to 60inch wg). Static Pressure rise is mostly due to momentum difference between blades at outlet and inlet. Increase in absolute velocity imparts velocity pressure to the impeller.
3. Radial Blades Fan: Blades are preprendicular to the axis of rotation. Radial Blade design is used for high pressure application. Although low in efficiency the design is excellent for dusty enviornment as the dust cannot stick on the blades because of geometry.