A centrifugal fan is a mechanical device for moving air or other gases. These fans increase the speed of air stream with the rotating impellers. They use the kinetic energy of the impellers or the rotating blade to increase the pressure of the air/gas stream which in turn moves them against the resistance caused by ducts, dampers and other components. Centrifugal fans accelerate air radially, changing the direction (typically by 90o) of the airflow. They are sturdy, quiet, reliable, and capable of operating over a wide range of conditions]
Centrifugal fans are constant CFM devices or constant volume devices, meaning that, at a constant fan speed, a centrifugal fan will pump a constant volume of air rather than a constant mass. This means that the air velocity in a system is fixed even though mass flow rate through the fan is not.
The centrifugal fan is one of the most widely used fans. These fans are widely used in the HVAC industry today. It is used in transporting gas or materials and in ventilation system for buildings.  They are also used commonly in central heating/cooling systems. They are also well-suited for industrial processes and air pollution control systems